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Title: Turning and Boring
A specialized treatise for machinists, students in the
industrial and engineering schools, and apprentices, on
turning and boring methods, etc.
Author: Franklin D. Jones
Release Date: October 4, 2010 [EBook #34030]
Language: English
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words in bold and italics have been transcribed as =word= and
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of text).
TURNING AND
BORING
A SPECIALIZED TREATISE FOR MACHINISTS,
STUDENTS IN INDUSTRIAL AND ENGINEERING
SCHOOLS, AND APPRENTICES, ON
TURNING AND BORING METHODS, INCLUDING
MODERN PRACTICE WITH ENGINE
LATHES, TURRET LATHES, VERTICAL AND
HORIZONTAL BORING MACHINES
BY FRANKLIN D. JONES
ASSOCIATE EDITOR OF MACHINERY
AUTHOR OF "PLANING AND MILLING"
_FIRST EDITION_
FIFTH PRINTING
NEW YORK
THE INDUSTRIAL PRESS
LONDON: THE MACHINERY PUBLISHING CO., LTD.
1919
COPYRIGHT, 1914
BY
THE INDUSTRIAL PRESS
NEW YORK
PREFACE
Specialization in machine-tool manufacture has been developed to such a
degree that there is need also for treatises which specialize on
different classes of tools and their application in modern practice.
This book deals exclusively with the use of various types of turning and
boring machines and their attachments, and is believed to be unusually
complete. In addition to standard practice, it describes many special
operations seldom or never presented in text-books. Very little space is
given to mere descriptions of different types of machine tools, the
principal purpose being to explain the use of the machine and the
practical problems connected with its operation, rather than the
constructional details. No attempt has been made to describe every
machine or tool which might properly be included, but rather to deal
with the more important and useful operations, especially those which
illustrate general principles.
Readers of mechanical literature are familiar with MACHINERY'S 25-cent
Reference Books, of which one hundred and twenty-five different titles
have been published during the past six years. Many subjects, however,
cannot be adequately covered in all their phases in books of this size,
and in response to a demand for more comprehensive and detailed
treatments on the more important mechanical subjects, it has been deemed
advisable to bring out a number of larger volumes, of which this is one.
This work includes much of the material published in MACHINERY'S
Reference Books Nos. 91, 92 and 95, together with a great amount of
additional information on modern boring and turning methods.
It is a pleasure to acknowledge our indebtedness to the manufacturers
who generously supplied illustrations and data, including many
interesting operations from actual practice. Much valuable information
was also obtained from MACHINERY.
F. D. J.
NEW YORK, _May, 1914_.
CONTENTS
PAGES
CHAPTER I
THE ENGINE LATHE--TURNING AND BORING OPERATIONS
General Description of an Engine Lathe--Example of Cylindrical
Turning--Facing the Ends Square with a Side-tool--Turning
Tool--Turning Work Cylindrical--Roughing and Finishing
Cuts--Filing and Finishing--Aligning Centers for Cylindrical
Turning--Application of Drivers or Dogs--Lathe Arbors or
Mandrels--Different Types of Lathe Arbors--Mandrel or Arbor
Press--Steadyrest for Supporting Flexible Parts--Application of
Steadyrest when Boring--The Follow-rest--Centering Parts to be
Turned--Centering Machine--Different Forms of Centers--Precaution
When Centering Tool Steel--Facing the Ends of Centered
Stock--Truing Lathe Centers--Universal, Independent and
Combination Chucks--Application of Chucks--Example of
Boring--Measuring Bored Holes--Setting Work in the
Chuck--Inaccuracy from Pressure of Chuck Jaws--Drilling and
Reaming--Holding Work on Faceplate--Application of Angle-plate to
Faceplate--Supporting Outer End of Chucked Work--Boring Large
Castings in the Lathe--Boring Holes to a Given Center
Distance--Turning Brass, Bronze and Copper--Machining Aluminum 1-53
CHAPTER II
LATHE TURNING TOOLS AND CUTTING SPEEDS
Turning Tools for General Work--Tool-holders with Inserted
Cutters--The Position of Turning Tools--Tool Grinding--Shape or
Contour of Cutting Edge--Direction of Top Slope for Turning
Tools--Clearance for the Cutting Edge--Angle of Tool-point and
Amount of Top Slope--Grinding a Lathe Tool--Cutting Speeds and
Feeds--Average Cutting Speeds for Turning--Factors which Limit
the Cutting Speed--Rules for Calculating Cutting Speeds--Feed of
Tool and Depth of Cut--Effect of Lubricant on Cutting
Speed--Lubricants Used for Turning--Lard Oil as a Cutting
Lubricant 54-79
CHAPTER III
TAPER TURNING--SPECIAL OPERATIONS--FITTING
Setting Tailstock Center for Taper Turning--Example of Taper
Turning--Setting the Tailstock Center with a Caliper
Tool--Setting the Tailstock Center with a Square--The Taper
Attachment--Application of Taper Attachment--Height of Tool
when Turning Tapers--Taper Turning with the Compound
Rest--Accurate Measurement of Angles and Tapers--To Find
Center Distance for a Given Taper--To Find Center Distance
for a Given Angle--To Find Angle for Given Taper per Foot--To
Find Angle for Given Disk Dimensions--Use of the Center
Indicator--Locating Work by the Button Method--Eccentric
Turning--Turning a Crankshaft in a Lathe--Special Crankshaft
Lathe--Operation of Special Crankshaft Lathe--Spherical
Turning--Spherical Turning Attachments--Turning with Front
and Rear Tools--A Multiple-tool Lathe--Examples of Multiple
Turning--Knurling in the Lathe--Relieving
Attachment--Application of Relieving Attachment--Relieving
Hobs or Taps Having Spiral Flutes--Classes of Fits Used in
Machine Construction--Forced Fits--Allowance for Forced
Fits--Pressure for Forced Fits--Allowance for Given
Pressure-Shrinkage Fits 80-134
CHAPTER IV
THREAD CUTTING IN THE LATHE
Selecting the Change Gears for Thread Cutting--The Thread
Tool--Cutting the Thread--Indicator or Chasing Dial for
Catching Threads--Principle of the Thread
Indicator--Replacing Sharpened Thread Tool--Use of Compound
Rest for Thread Cutting--Threads Commonly Used--Multiple
Threads--Cutting a U. S. Standard Thread--Cutting a Left-hand
Thread--Cutting a Square Thread--Cutting Multiple
Threads--Setting Tool When Cutting Multiple Threads--Taper
Threading--Internal Threading--Stop for Thread Tools--The
Acme Standard Thread--The Whitworth Thread--Worm
Threads--Coarse Threading Attachment--Testing the Size of a
Thread--The Thread Micrometer--Three-wire System of Measuring
Threads--Rivett-Dock Threading Tool--Cutting Screws to
Compensate for Shrinkage--Calculating Change Gears for Thread
Cutting--Lathes with Compound Gearing--Fractional
Threads--Change Gears for Metric Pitches--Quick Change-gear
Type of Lathe 135-177
CHAPTER V
TURRET LATHE PRACTICE
General Description of a Turret Lathe--Example of Turret
Lathe Work--Machining Flywheels in Turret Lathe--Finishing a
Flywheel at One Setting in Turret Lathe--Finishing a Webbed
Flywheel in Two Settings--Tools for Turret
Lathes--Box-tools--Examples of Box-tool Turning--Hollow
Mills--Releasing Die and Tap Holders--Self-opening Die
Heads--Collapsing Taps--Miscellaneous Turret Lathe
Tools--Turning Gasoline Engine Pistons in Turret
Lathe--Turning Piston Rings in Turret Lathe--Piston Turning
in Pratt and Whitney Turret Lathe--Attachment for Turning
Piston Rings--Turning Worm-gear Blanks in Turret
Lathe--Turning Bevel Gear Blanks--Shell Turning Operation in
Flat Turret Lathe--Chuck Work in Flat Turret
Lathe--Double-spindle Flat Turret Lathe--Automatic Chucking
and Turning Machine--Example of Work on Automatic Turning
Machine--Determining Speed and Feed Changes--Setting the
Turret Slide--Setting the Cross-slide Cam--Setting the Boring
Tool for Recessing--Adjustments for Automatic Feed and Speed
Changes--Turning Flywheel in Automatic Chucking and Turning
Machine--Automatic Multiple-spindle Chucking
Machine--Selecting Type of Turning Machine 178-241
CHAPTER VI
VERTICAL BORING MILL PRACTICE
Boring and Turning in a Vertical Boring Mill--Holding and
Setting Work on Boring Mill Table--Turning in a Boring
Mill--Boring Operations--Turning Tools for the Vertical
Boring Mill--Turning a Flywheel on a Vertical Mill--Convex
Turning Attachment for Boring Mills--Turning Taper or Conical
Surfaces--Turret-lathe Type of Vertical Boring Mill--Examples
of Vertical Turret Lathe Work--Floating Reamer
Holders--Multiple Cylinder Boring Machine 242-274
CHAPTER VII
HORIZONTAL BORING MACHINES
Horizontal Boring Machine with Vertical Table
Adjustment--Drilling and Boring--Cutters Used--Cutter-heads
for Boring Large Holes--Cylinder Boring--Boring a Duplex
Gasoline Engine Cylinder--Examples of Boring, Radial Facing
and Milling--Fixture for Cylinder Lining or
Bushing--Horizontal Boring Machine of Floor Type 275-297
INDEX 299-307
TURNING AND BORING
CHAPTER I
THE ENGINE LATHE--TURNING AND BORING OPERATIONS
The standard "engine" lathe, which is the type commonly used by
machinists for doing general work, is one of the most important tools in
a machine shop, because it is adapted to a great variety of operations,
such as turning all sorts of cylindrical and taper parts, boring holes,
cutting threads, etc. The illustration Fig. 1 shows a lathe which, in
many respects, represents a typical design, and while some of the parts
are arranged differently on other makes, the general construction is
practically the same as on the machine illustrated.
The principal parts are the bed _B_, the headstock _H_, the tailstock
_T_, and the carriage _C_. The headstock contains a spindle which is
rotated by a belt that passes over the cone-pulley _P_, and this spindle
rotates the work, which is usually held between pointed or conical
centers _h_ and _h_{1}_ in the headstock and tailstock, or in a chuck
screwed onto the spindle instead of the faceplate _F_. The carriage _C_
can be moved lengthwise along the bed by turning handle _d_, and it can
also be moved by power, the movement being transmitted from the
headstock spindle either through gears _a_, _b_, _c_, and lead-screw
_S_, or by a belt operating on pulleys _p_ and _p_{1}_, which drive the
feed-rod _R_. The lead-screw _S_ is used when cutting threads, and the
feed-rod _R_ for ordinary turning operations; in this way the wear on
the lead-screw is reduced and its accuracy is preserved.
[Illustration: Fig. 1. Bradford Belt-driven Lathe--View of Front or
Operating Side]
On the carriage, there is a cross-slide _D_ which can be moved at right
angles to the lathe bed by handle _e_, and on _D_ there is an upper or
compound slide _E_ which can be swiveled to different positions. The
tool _t_, that does the turning, is clamped to the upper slide, as
shown, and it can be moved with relation to the work by the movement of
the carriage _C_ along the bed, or by moving slide _D_ crosswise. The
lengthwise movement is used to feed the tool along the work when
turning, boring or cutting a screw, and the crosswise movement for
facing the ends of shafts, etc., or for radial turning. When the tool is
to be fed at an angle, other than at right angles to the bed, slide _E_,
which can be set to the required angle, is used. The lengthwise and
crosswise feeding movements can be effected by power, the lengthwise
feed being engaged by tightening knob _k_, and the cross-feed by
tightening knob _l_. The direction of either of these movements can also
be reversed by shifting lever _r_. Ordinarily the carriage and slide are
adjusted by hand to bring the tool into the proper position for turning
to the required diameter, and then the power feed (operating in the
desired direction) is engaged. The tailstock _T_ can be clamped in
different positions along the bed, to suit the length of the work, and
its center _h_{1}_ can be moved in or out for a short distance, when
adjusting it to the work, by turning handle _n_.
[Illustration: Fig. 2. Plan View of Lathe Headstock showing Back-gears]
[Illustration: Fig. 3. Feed Mechanism of Lathe Apron]
As some metals are much harder than others, and as the diameters of
parts to be turned also vary considerably, speed changes are necessary,
because if the speed is excessive, the turning tool will become dull in
too short a time. These speed changes (with a belt-driven lathe) are
obtained by placing the driving belt on different steps of cone-pulley
_P_, and also by the use of back-gears. The cone-pulley can be connected
directly with the spindle or be disengaged from it by means of bolt _m_.
When the pulley and spindle are connected, five speeds (with this
particular lathe) are obtained by simply shifting the driving belt to
different steps of the cone. When a slower speed is required than can be
obtained with the belt on the largest step of the cone, the latter is
disconnected from the spindle, and the back-gears _G_ and _G_{1}_ (shown
in the plan view Fig. 2) are moved forward into mesh by turning handle
_O_; the drive is then from cone-pulley _P_ and gear _L_ to gear _G_,
and from gear _G_{1}_ to the large gear _J_ on the spindle. When driving
through the back-gears, five more speed changes are obtained by shifting
the position of the driving belt, as before. The fastest speed with the
back-gears in mesh is somewhat slower than the slowest speed when
driving direct or with the back-gears out of mesh; hence, with this
particular lathe, a series of ten gradually increasing speeds is
obtained. Changes of feed for the turning tool are also required, and
these are obtained by shifting the belt operating on pulleys _p_ and
_p_{1}_ to different-sized steps. On some lathes these feed changes are
obtained through gears which can be shifted to give different ratios.
Many lathes also have gears in the headstock for changing the speeds.
[Illustration: Fig. 4. Rear View of Lathe Apron]
Front and rear views of the carriage apron, which contains the feeding
mechanism, are shown in Figs. 3 and 4, to indicate how the feeds are
engaged and reversed. The feed-rod _R_ (Fig. 1) drives the small bevel
gears _A_ and _A_{1}_ (Figs. 3 and 4), which are mounted on a slide _S_
that can be moved by lever _r_ to bring either bevel gear into mesh with
gear _B_. Gear _B_ is attached to pinion _b_ (see Fig. 3) meshing with
gear _C_, which, when knob _k_ (Fig. 1) is tightened, is locked by a
friction clutch to pinion _c_. The latter pinion drives gear _D_ which
rotates shaft _E_. A pinion cut on the end of shaft _E_ engages rack _K_
(Fig. 1) attached to the bed, so that the rotation of _E_ (which is
controlled by knob _k_) moves the carriage along the bed. To reverse the
direction of the movement, it is only necessary to throw gear _A_ into
mesh and gear _A_{1}_ out, or _vice versa_, by operating lever _r_. When
the carriage is traversed by hand, shaft _E_ and gear _D_ are rotated by
pinion _d_{1}_ connected with handle _d_ (Fig. 1).
The drive for the cross-feed is from gear _C_ to gear _F_ which can be
engaged through a friction clutch (operated by knob _l_, Fig. 1) with
gear _G_ meshing with a pinion _H_. The latter rotates the cross-feed
screw, which passes through a nut attached to slide _D_ (Fig. 1), thus
moving the latter at right angles to the ways of the bed. The cross-feed
is also reversed by means of lever _r_. As previously explained,
lead-screw _S_ is only used for feeding the carriage when cutting
threads. The carriage is engaged with this screw by means of two
half-nuts _N_ (Fig. 4) that are free to slide vertically and are closed
around the screw by operating lever _u_. These half-nuts can only be
closed when lever _r_ is in a central or neutral position, so that the
screw feed and the regular turning feed cannot be engaged at the same
time. As previously mentioned, lead-screw _S_, Fig. 1, is rotated from
the lathe spindle, through gears _a_, _b_ and _c_, called change gears.
An assortment of these gears, of various sizes, is provided with the
lathe, for cutting screws of different pitch. The gears to use for any
pitch within the range of the lathe are given on the plate _I_.
=Example of Cylindrical Turning.=--Having now considered the principal
features of what might be called a standard lathe, the method of using
it in the production of machine parts will be explained. To begin with a
simple example of work, suppose a steel shaft is to be turned to a
diameter of 2-1/4 inches and a length of 14-1/2 inches, these being the
finished dimensions. We will assume that the rough stock is cut off to a
length of 14-5/8 inches and has a diameter of 2-5/8 inches. The first
step in this operation is to form conically shaped center-holes in each
end of the piece as indicated at _c_ in Fig. 5. As all work of this kind
is held, while being turned, between the centers _h_ and _h_{1}_, holes
corresponding in shape to these centers are necessary to keep the work
in place. There are several methods of forming these center-holes, as
explained later.
After the work is centered, a dog _A_ is clamped to one end by
tightening screw _s_; it is then placed between the centers of the
lathe. The dog has a projecting end or "tail," as it is commonly called,
which enters a slot in the faceplate _F_ and thereby drives or rotates
the work, when power is applied to the lathe spindle onto which the
faceplate is screwed. The tailstock center _h_1_, after being oiled,
should be set up just tight enough to eliminate all play, without
interfering with a free rotary movement of the work. This is done by
turning handle _n_, and when the center is properly adjusted, the
tailstock spindle containing the center is locked by tightening handle
_p_. (Ordinary machine oil is commonly used for lubricating lathe
centers, but a lubricant having more "body" should be used, especially
when turning heavy parts. The following mixtures are recommended: 1. Dry
or powdered red lead mixed with a good grade of mineral oil to the
consistency of cream. 2. White lead mixed with sperm oil with enough
graphite added to give the mixture a dark lead color.)
[Illustration: Fig. 5. Plan View showing Work Mounted between Centers of
Lathe]
=Facing the Ends Square with a Side-tool.=--Everything is now ready for
the turning operation. The ends of the piece should be faced square
before turning the body to size, and the tool for this squaring
operation is shown in Fig. 6; this is known as a side-tool. It has a
cutting edge _e_ which shaves off the metal as indicated in the end view
by the dotted lines. The side _f_ is ground to an angle so that when
the tool is moved in the direction shown by the arrow, the cutting edge
will come in contact with the part to be turned; in other words, side
_f_ is ground so as to provide clearance for the cutting edge. In
addition, the top surface against which the chip bears, is beveled to
give the tool keenness so that it will cut easily. As the principles of
tool grinding are treated separately in Chapter II we shall for the
present consider the tool's use rather than its form.
[Illustration: Fig. 6. Lathe Side-tool for Facing Ends of Shafts, etc.]
For facing the end, the side tool is clamped in the toolpost by
tightening the screw _u_, Fig. 5, and it should be set with the cutting
edge slightly inclined from a right-angled position, the point being in
advance so that it will first come into contact with the work. The
cutting edge should also be about the same height as the center of the
work. When the tool is set, the lathe (if belt-driven) is started by
shifting an overhead belt and the tool is then moved in until the point
is in the position shown at _A_, Fig. 7. The tool-point is then fed
against the end by handle _d_, Fig. 5, until a light chip is being
turned off, and then it is moved outward by handle _e_ (as indicated by
the arrow at _B_, Fig. 7), the carriage remaining stationary. As the
movement of the tool-point is guided by the cross-slide _D_, which is at
right angles with the axis of the work, the end will be faced square.
For short turning operations of this kind, the power feeds ordinarily
are not used as they are intended for comparatively long cuts. If it
were necessary to remove much metal from the end, a number of cuts would
be taken across it; in this case, however, the rough stock is only 1/8
inch too long so that this end need only be made true.
[Illustration: Fig. 7. Facing End with Side-tool and Turning Work
Cylindrical]
After taking a cut as described, the surface, if left rough by the
tool-point, should be made smooth by a second or finishing cut. If the
tool is ground slightly round at the point and the cutting edge is set
almost square, as at _C_, Fig. 7, a smooth finish can be obtained; the
cut, however, should be light and the outward feed uniform. The work is
next reversed in the centers and the driving dog is placed on the end
just finished; the other end is then faced, enough metal being removed
to make the piece 14-1/2 inches long, as required in this particular
case. This completes the facing operation. If the end of the work does
not need to be perfectly square, the facing operation can be performed
by setting the tool in a right-angled position and then feeding it
sidewise, thus removing a chip equal to the width of one side. Evidently
this method is confined to comparatively small diameters and the
squareness of the turned end will be determined by the position of the
tool's cutting edge.
=Turning Tool--Turning Work Cylindrical.=--The tool used to turn the
body to the required diameter is shaped differently from the side-tool,
the cutting edge _E_ of most tools used for plain cylindrical turning
being curved as shown in Fig. 8. A tool of this shape can be used for a
variety of cylindrical turning operations. As most of the work is done
by that part of the edge marked by arrow _a_, the top of the tool is
ground to slope back from this part to give it keenness. The end _F_, or
the flank, is also ground to an angle to provide clearance for the
cutting edge. If the tool did not have this clearance, the flank would
rub against the work and prevent the cutting edge from entering the
metal. This type of tool is placed about square with the work, for
turning, and with the cutting end a little above the center.
[Illustration: Fig. 8. Tool used for Cylindrical Turning]
Before beginning to turn, a pair of outside calipers or a micrometer
should be set to 2-1/4 inches, which, in this case, is the finished
diameter of the work. Calipers are sometimes set by using a graduated
scale as at _A_, Fig. 9, or they can be adjusted to fit a standard
cylindrical gage of the required size as at _B_. Very often fixed
caliper gages _C_ are used instead of the adjustable spring calipers.
These fixed gages, sometimes called "snap" gages, are accurately made to
different sizes, and they are particularly useful when a number of
pieces have to be turned to exactly the same size.
The turning tool is started at the right-hand end of the work and the
tool should be adjusted with the left hand when beginning a cut, as
shown in Fig. 10, in order to have the right hand free for calipering. A
short space is first turned by hand feeding, as at _D_, Fig. 7, and when
the calipers show that the diameter is slightly greater than the
finished size (to allow for a light finishing cut, either in the lathe
or grinding machine) the power feed for the carriage is engaged; the
tool then moves along the work, reducing it as at _E_. Evidently, if the
movement is along a line _b--b_, parallel with the axis _a--a_, the
diameter _d_ will be the same at all points, and a true cylindrical
piece will be turned. On the other hand, if the axis _a--a_ is inclined
one way or the other, the work will be made tapering; in fact, the
tailstock center _h_1_ can be adjusted laterally for turning tapers, but
for straight turning, both centers must be in alignment with the
carriage travel. Most lathes have lines on the stationary and movable
parts of the tailstock base which show when the centers are set for
straight turning. These lines, however, may not be absolutely correct,
and it is good practice to test the alignment of the centers before
beginning to turn. This can be done by taking trial cuts, at each end of
the work (without disturbing the tool's crosswise position), and then
comparing the diameters, or by testing the carriage travel with a true
cylindrical piece held between the centers as explained later.
[Illustration: Fig. 9. Setting Calipers by Scale--Setting by Gage--Fixed
Gage]
If the relative positions of the lathe centers are not known, the work
should be calipered as the cut progresses to see if the diameter _d_ is
the same at all points. In case the diameter gradually increases, the
tailstock center should be shifted slightly to the rear before taking
the next cut, but if the diameter gradually diminishes, the adjustment
would, of course, be made in the opposite direction. The diameter is
tested by attempting to pass the calipers over the work. When the
measuring points just touch the work as they are gently passed across
it, the diameter being turned is evidently the same as the size to which
the calipers are set.
[Illustration: Fig. 10. Views showing how the Cross-slide and Carriage
are Manipulated by Hand when Starting a Cut--View to Left, Feeding Tool
Laterally; View to Right, Feeding Tool in a Lengthwise Direction]
As the driving dog is on one end, the cut cannot be taken over the
entire length, and when the tool has arrived at say position _x_, Fig.
5, it is returned to the starting point and the work is reversed in the
centers, the dog being placed upon the other end. The unfinished part is
then turned, and if the cross-slide is not moved, the tool will meet the
first cut. It is not likely that the two cuts will be joined or blended
together perfectly, however, and for this reason a cut should be
continuous when this is possible.
=Roughing and Finishing Cuts.=--Ordinarily in lathe work, as well as in
other machine work, there are two classes of cuts, known as "roughing"
and "finishing" cuts. Roughing cuts are for reducing the work as
quickly as possible almost to the required size, whereas finishing cuts,
as the name implies, are intended to leave the part smooth and of the
proper size. When the rough stock is only a little larger than the
finished diameter, a single cut is sufficient, but if there is
considerable metal to turn away, one or more deep roughing cuts would
have to be taken, and, finally, a light cut for finishing. In this
particular case, one roughing and one finishing cut would doubtless be
taken, as the diameter has to be reduced 3/8 inch. Ordinarily the
roughing cut would be deep enough to leave the work about 1/32 or
perhaps 1/16 inch above the finished size. When there is considerable
metal to remove and a number of roughing cuts have to be taken, the
depth of each cut and the feed of the tool are governed largely by the
pulling power of the lathe and the strength of the work to withstand the
strain of a heavy cut. The depth of roughing cuts often has to be
reduced considerably because the part being turned is so flexible that a
heavy cut would spring the work and cause the tool to gouge in. Of
course, just as few cuts as possible should be taken in order to save
time. The speed of the work should also be as fast as the conditions
will allow for the same reason, but as there are many things which
govern the speed, the feed of the tool, and the depth of the cut, these
important points are referred to separately in Chapter II.
=Filing and Finishing.=--In many cases the last or finishing cut does
not leave as smooth a surface as is required and it is necessary to
resort to other means. The method commonly employed for finishing in the
lathe is by the use of a file and emery cloth. The work is rotated
considerably faster for filing than for turning, and the entire surface
is filed by a flat, single-cut file, held as shown in Fig. 11. The file
is passed across the work and advanced sidewise for each forward stroke,
until the entire surface is finished. The file should be kept in contact
with the work continually, but on the return stroke the pressure should
be relieved. The movement of the file during the forward or cutting
stroke should be much slower than when filing in a vise. By moving the
file slowly, the work can make a number of revolutions for each stroke,
which tends to keep it round, as practically the same amount of metal is
removed from the entire circumference. On the other hand, short rapid
strokes tend to produce flat spots, or at least an irregular surface,
especially if the work can only make part of a revolution for each
cutting stroke. The pressure on the file during the forward stroke
should also be kept as nearly uniform as possible.
[Illustration: Fig. 11. Filing Work after Finishing Cut is taken]
It is very difficult to file a part smooth and at the same time to keep
it round and cylindrical, and the more filing that has to be done, the
greater the chance of error. For this reason, the amount left for filing
should be very small; in fact, the metal removed by filing should be
just enough to take out the tool marks and give a smooth finish. Very
often a satisfactory finish can be obtained with a turning tool, and
filing is not necessary at all. The file generally used for lathe work
is a "single-cut bastard" of "mill" section, having a length of from 12
to 14 inches.
Sometimes particles of metal collect between the teeth of a file and
make deep scratches as the file is passed across the work. When this
occurs, the teeth should be cleaned by using a wire brush or a file
card, which is drawn across the file in the direction of the teeth. This
forming of tiny particles between the teeth is known as "pinning" and it
can sometimes be avoided by rubbing chalk on the file. Filing is not
only done to obtain a smooth finish, but also to reduce the work to an
exact diameter, as a very slight reduction can be made in this way.
[Illustration: Fig. 12. Two Methods of Aligning Centers for Cylindrical
Turning]
If a polish is desired, this can be obtained by holding a piece of emery
cloth tightly around the work as it revolves. The coarseness of emery
cloth is indicated by letters and numbers corresponding to the grain
number of loose emery. The letters and numbers for grits ranging from
fine to coarse are as follows: _FF_, _F_, 120, 100, 90, 80, 70, 60, 54,
46, 40. For large work roughly filed, use coarse cloth such as Nos. 46
or 54, and then finer grades to obtain the required polish. If the work
has been carefully filed, a good polish can be obtained with Nos. 60 and
90 cloth, and a brilliant polish by finishing with No. 120 and
flour-emery.
Most cylindrical parts can be finished more quickly and accurately in
the grinder than in the lathe, and many classes of work are, at the
present time, simply rough-turned in the lathe and then ground to size
in a cylindrical grinding machine.
=Aligning Centers for Cylindrical Turning.=--When a rod or shaft must be
turned cylindrical or to the same diameter throughout its entire length,
it is good practice to test the alignment of the centers, before
inserting the work. The position of the tailstock center for cylindrical
turning may be indicated by the coincidence of graduation marks on the
base, but if accuracy is necessary, the relative position of the two
centers should be determined in a more positive way. A very simple and
convenient method of testing the alignment is shown at _A_ in Fig. 12.
The work is first turned for a short distance, near the dogged end, as
shown, and the tool is left as set for this cut; then the tailstock
center is withdrawn and the work is moved sufficiently to permit running
the tool back to the tailstock end without changing its original
setting. A short cut is then taken at this end and the diameters _d_ and
_d_{1}_ are carefully compared. In case there is any variation, the
tailstock center is adjusted laterally, other trial cuts are taken, and
the test repeated.
Another method is illustrated at _B_, which requires the use of a
test-bar _t_. This bar should have accurately made centers and the ends
finished to exactly the same diameter. The lathe centers are aligned by
placing the bar between them and then testing the position of the ends.
This can be done by comparing each end with a tool held in the toolpost
and moved from one to the other by shifting the carriage, but a better
method is to clamp a test indicator _i_ in the toolpost and bring it in
contact with first one end of the bar and then the other. If the dial
does not register the same at each end, it shows that the lathe centers
are not in line. Even when centers are correctly set, lathes that have
been in use a long time do not always turn cylindrical or straight,
because if the ways that guide the carriage are worn unevenly, the tool
as it moves along does not remain in the same plane and this causes a
variation in the diameter of the part being turned.
=Application of Drivers or Dogs.=--Work that is turned between centers
is sometimes driven by a dog which is so short for the faceplate that
the bent driving end bears against the bottom _a_ of the faceplate slot,
as shown at _A_, Fig. 13. If the dog is nearly the right length, it may
allow the headstock center to enter the center in the work part way,
with the result that the turned surface is not true with the centers.
When a driving dog of this type is used, care should be taken to see
that it moves freely in the faceplate slot and does not bind against the
bottom. By using a straight dog (_B_), which is driven by a pin _b_
bolted to the faceplate, all danger from this source is eliminated. The
straight dog, however, is used more particularly to do away with the
leverage _l_ of a bent dog, as this leverage tends to spring a flexible
part when a cut is being taken.
[Illustration: Fig. 13. (A) Dog that is too Short for Faceplate. (B)
Straight Driving Dog]
Straight dogs are also made with two driving ends which engage pins on
opposite sides of the faceplate. This type is preferable because it
applies the power required for turning, evenly to the work, which still
further reduces the tendency to spring it out of shape. The principal
objection to the double-ended type lies in the difficulty of adjusting
the driving pins so that each bears with equal pressure against the dog.
The double-ended driver is often used for large work especially if deep
roughing cuts are necessary.
=Lathe Arbors or Mandrels.=--When it is necessary to turn the outside of
a part having a hole through it, centers cannot, of course, be drilled
in the ends and other means must be resorted to. We shall assume that
the bushing _B_, Fig. 14, has a finished hole through the center, and
it is desired to turn the outside cylindrical and concentric with the
hole. This could be done by forcing a tightly-fitted arbor _M_, having
accurately-centered ends, into the bushing and inserting the mandrel and
work between the lathe centers _h_ and _h_{1}_ as shown. Evidently, if
the arbor runs true on its centers, the hole in the bushing will also
run true and the outside can be turned the same as though the arbor and
bushing were a solid piece. From this it will be seen that an arbor
simply forms a temporary support for parts that are bored and therefore
cannot be centered.
[Illustration: Fig. 14. Bushing mounted on Arbor for Turning]
Another example of work that would be turned on an arbor is shown in
Fig. 15. This is a small cast-iron wheel having a finished hole through
the hub, and the outer surface and sides of the rim are to be turned
true with this hole. In this case, the casting would also be held by
pressing a mandrel through the hub; as shown. This method, however,
would only apply to comparatively small wheels because it would be
difficult, if not impossible, to prevent a large wheel from turning on
the arbor when taking a cut, and even if it could be driven, large work
could be done to better advantage on another type of machine. (The
vertical boring mill is used extensively for turning large wheels, as
explained in Chapter VI.) When turning the outside of the rim, a tool
similar to that shown at _t_ should be used, but for facing or turning
the sides, it might be better, if not necessary, to use tools having
bent ends as shown by the dotted lines; in fact, turning tools of
various kinds are made with the ends bent to the right or left, as this
enables them to be used on surfaces that could not be reached very well
with a straight tool. If a comparatively large pulley is mounted near
the end of the arbor, it can be driven directly by pins attached to the
faceplate and engaging the pulley arms. This method of driving is often
employed when the diameter to be turned is large and the hole for the
arbor is so small that there will not be sufficient friction for
driving.
[Illustration: Fig. 15. Turning Pulley Held on an Arbor]
=Different Types of Lathe Arbors.=--Three different types of lathe
arbors are shown in Fig. 16. The kind shown at _A_ is usually made of
tool steel and the body is finished to a standard size. The ends are
somewhat reduced and flat spots are milled, as shown, to give the
clamping screw of the dog a good grip. The body of the arbor is usually
tapered about 0.006 inch per foot. This taper makes it easier to insert
the arbor in a close-fitting hole, and it also permits slight variations
in the diameter of different holes. As to hardening, the practice at the
present time among manufacturers is to harden arbors all over, but for
extremely accurate work, an arbor having hardened ends and a soft body
is generally considered superior, as there is less tendency of
distortion from internal stresses. Hardened arbors are "seasoned" before
finish-grinding to relieve these internal stresses.
The solid type _A_, Fig. 16, is used very extensively, but in shops
where a great variety of work is being done and there are many odd-sized
holes, some form of expanding arbor _B_ can be used to advantage. This
type, instead of being solid, consists of a tapering inner arbor _M_ on
which is placed a split bushing that can be expanded, within certain
limits, by driving in the tapering member. The advantage of this type is
that a comparatively small stock of arbors is required, as
different-sized bushings can be used. This type can also be fitted to
holes of odd sizes, whereas a solid arbor must be provided for each
different size hole, unless the variation is very slight. The latter
are, however, more accurate than the expanding type.
[Illustration: Fig. 16. Different Types of Lathe Arbors]
Another form of expanding arbor is shown at _C_. This type has a
straight body _N_ in which four tapering grooves are cut lengthwise, as
shown, and there is a sleeve _S_, containing four slots that are located
to correspond with the tapering grooves. Strips s are fitted into these
slots, and as the part _N_ is driven in, the strips are moved outward as
they ascend the tapering grooves. By having different sets of these
strips of various heights, one arbor of this type can be made to cover
quite a range of sizes. It is not suited, however, to thin work, as the
pressure, being concentrated in four places, would spring a flexible
part out of shape.
The cone arbor or mandrel shown at _A_, in Fig. 17, is convenient for
holding parts having comparatively large holes, as it can be adjusted
for quite a range of diameters. The work is gripped between the two
cones _c_ and _c_{1}_ which are forced together by nut _n_. The cones
are prevented from turning upon the arbor by keys. This style of arbor
should not be used for accurate work. The threaded arbor _B_ is used for
facing the sides of nuts square with the tapped hole. When a nut is
first put upon the arbor, the rough side comes against an equalizing
washer _w_. This washer rests against a spherical seat so that it can
shift to provide a uniform bearing for the rough side of the nut, even
though it is not square with the tapped hole. This feature prevents the
nut from being canted on the arbor and insures an accurately faced nut.
The revolving conical center shown at _C_ is often used for holding a
pipe or tube while turning the outside. The cone is adjusted to fit into
the hole of the pipe, by means of the tailstock spindle, and the
opposite end is usually held in a chuck.
[Illustration: Fig. 17. (A) Cone Arbor. (B) Nut Arbor. (C) Pipe Center]
Particular care should be taken to preserve the accuracy of the centers
of lathe arbors by keeping them clean and well-oiled while in use.
=Mandrel or Arbor Press.=--The best method of inserting an arbor of the
solid type in a hole is by using a press, Fig. 18, designed for that
purpose, but if such a press is not available and it is necessary to
drive the mandrel in, a "soft" hammer, made of copper, lead or other
soft material, should be used to protect the centered end of the arbor.
In either case, the arbor should not be forced in too tightly, for if it
fits properly, this will not be necessary in order to hold the work
securely. On the other hand, the work might easily be broken by
attempting to force the arbor in as far and as tightly as possible. In
using the arbor press, the work is placed on the base _B_ with the hole
in a vertical position, and the arbor (which should be oiled slightly)
is forced down into it by ram _R_, operated by lever _L_. Slots are
provided in the base, as shown, so that the end of the arbor can come
through at the bottom of the hole. The lever of this particular press is
counter-weighted so that it rises to a vertical position when released.
The ram can then be adjusted quickly to any required height by the
handwheel seen at the left.
[Illustration: Fig. 18. Press for Forcing Arbors into Work]
Some shops are equipped with power-driven mandrel or arbor presses.
This type is particularly desirable for large work, owing to the greater
pressure required for inserting mandrels that are comparatively large in
diameter. One well-known type of power press is driven by a belt, and
the downward pressure of the ram is controlled by a handwheel. The ram
is raised or lowered by turning this handwheel in one direction or the
other, and a gage shows how much pressure is being applied. This type of
press can also be used for other purposes, such as forcing bushings or
pins into or out of holes, bending or straightening parts, or for
similar work.
[Illustration: Fig. 19. Steadyrest and Follow-rest for Supporting
Flexible Parts]
=Steadyrest for Supporting Flexible Parts.=--Occasionally long slender
shafts, rods, etc., which have to be turned, are so flexible that it is
necessary to support them at some point between the lathe centers. An
attachment for the lathe known as a steadyrest is often used for this
purpose. A steadyrest is composed of a frame containing three jaws _J_
(Fig. 19), that can be adjusted in or out radially by turning screws
_S_. The frame is hinged at _h_, thus allowing the upper half to be
swung back (as shown by the dotted lines) for inserting or removing the
work. The bolt-clamp _c_ holds the hinged part in the closed position.
The base of the frame has V-grooves in it that fit the ways of the lathe
bed. When the steadyrest is in use, it is secured to the bed by clamp
_C_, and the jaws _J_ are set in against the work, thus supporting or
steadying it during the turning operation. The steadyrest must, of
course, be located at a point where it will not interfere with the
turning tool.
[Illustration: Fig. 20. Application of Steadyrest to a Flexible Rod]
Fig. 20 shows the application of the steadyrest to a long forged rod,
having one small end, which makes it too flexible to be turned without
support. As this forging is rough, a true surface _n_ a little wider
than the jaws _J_ (Fig. 19) is first turned as a bearing for the jaws.
This should be done very carefully to prevent the work from mounting the
tool. A sharp pointed tool should be used and very light cuts taken. The
steadyrest is next clamped to the lathe bed opposite the turned surface,
and the jaws are adjusted in against this surface, thus forming a
bearing. Care should be taken not to set up the jaws too tightly, as the
work should turn freely but without play. The large part of the rod and
central collar are then turned to size, this half being machined while
the small part is in the rough and as stiff as possible. The rod is then
reversed and the steadyrest is applied to the part just finished, as
shown at _B_, thus supporting the work while the small end is being
turned. That part against which the jaws bear should be kept well oiled,
and if the surface is finished it should be protected by placing a strip
of emery cloth beneath the jaws with the emery side out; a strip of
belt leather is also used for this purpose, the object in each case
being to prevent the jaws from scratching and marring the finished
surface, as they tend to do, especially if at all rough.
If the work were too flexible to permit turning a spot at _n_, this
could be done by first "spotting" it at some point _o_, and placing the
steadyrest at that point while turning another spot at _n_.
Sometimes it is desirable to apply a steadyrest to a surface that does
not run true and one which is not to be turned; in such a case a device
called a "cat-head" is used. This is simply a sleeve _S_ (Fig. 21) which
is placed over the untrue surface to serve as a bearing for the
steadyrest. The sleeve is made to run true by adjusting the four
set-screws at each end, and the jaws of the steadyrest are set against
it, thus supporting the work.
[Illustration: Fig. 21. Cat-head which is sometimes used as Bearing for
Steadyrest]
=Application of Steadyrest when Boring.=--Another example illustrating
the use of the steadyrest is shown in Fig. 22. The rod _R_ is turned on
the outside and a hole is to be bored in the end (as shown by dotted
lines) true with the outer surface. If the centers used for turning the
rod are still in the ends, as they would be ordinarily, this work could
be done very accurately by the following method: The rod is first placed
between the centers as for turning, with a driving dog _D_ attached, and
the steadyrest jaws _J_ are set against it near the outer end, as shown.
Before any machine work is done, means must be provided for holding the
rod back against the headstock center _h_, because, for an operation of
this kind, the outer end cannot be supported by the tailstock center;
consequently the work tends to shift to the right. One method of
accomplishing this is shown in the illustration. A hardwood piece _w_,
having a hole somewhat larger than the work, is clamped against the dog,
in a crosswise position, by the swinging bolts and thumb-screws shown.
If the dog is not square with the work, the wood piece should be canted
so that the bearing will not be all on one side. For large heavy parts a
similar "bridle" or "hold-back"--as this is commonly called--is made by
using steel instead of wood for the part _w_. Another very common method
which requires no special equipment is illustrated in Fig. 23. An
ordinary leather belt lacing _L_ is attached to the work and faceplate
while the latter is screwed off a few turns as shown. Then the lacing is
drawn up by hand and tied, and the faceplate is screwed onto the
spindle, thus tightening the lacing and drawing the work against the
headstock center. The method of applying the lacing is quite clearly
indicated in the illustration. If a small driving faceplate is used, it
may be necessary to drill holes for the belt lacing, as shown.
[Illustration: Fig. 22. Shaft supported by Steadyrest for Drilling and
Boring End]
A hole is next drilled in the end of the rod by using a twist drill in
the tailstock. If the hole is finished by boring, a depth mark should
be made on the tool shank that will warn the workman of the cutting
end's approach to the bottom. A chuck can also be used in connection
with a steadyrest for doing work of this kind, as shown in Fig. 24, the
end of the rod being held and driven by the chuck _C_. If the piece is
centered, it can be held on these centers while setting the steadyrest
and adjusting the chuck, but if the ends are without centers, a very
good way is to make light centers in the ends with a punch; after these
are properly located they are used for holding the work until the
steadyrest and chuck jaws have been adjusted. In case it is necessary to
have the end hole very accurate with the outside of the finished rod, a
test indicator _I_ should be applied to the shaft as shown. This is an
instrument which shows with great accuracy whether a rotating part runs
true and it is also used for many other purposes in machine shops. The
indicator is held in the lathe toolpost and the contact point beneath
the dial is brought against the work. If the latter does not run true,
the hand of the indicator vibrates and the graduations on the dial show
how much the work is out in thousandths of an inch.
[Illustration: Fig. 23. Hold-back used when Outer End of Work is held in
Steadyrest]
=The Follow-rest.=--When turning long slender parts, such as shafts,
etc., a follow-rest is often used for supporting the work. The
follow-rest differs from the steadyrest in that it is attached to and
travels with the lathe carriage. The type illustrated to the right in
Fig. 19 has two adjustable jaws which are located nearly opposite the
turning tool, thus providing support where it is most needed. In using
this rest, a cut is started at the end and the jaws are adjusted to this
turned part. The tool is then fed across the shaft, which cannot spring
away from the cut because of the supporting jaws. Some follow-rests
have, instead of jaws, a bushing bored to fit the diameter being turned,
different bushings being used for different diameters. The bushing forms
a bearing for the work and holds it rigidly. Whether a bushing or jaws
are used, the turning tool is slightly in advance of the supporting
member.
[Illustration: Fig. 24. Testing Work with Dial Indicator]
=Centering Parts to be Turned.=--As previously mentioned, there are a
number of different methods of forming center-holes in the ends of parts
that have to be turned while held between lathe centers. A method of
centering light work, and one that requires few special tools, is first
to locate a central point on the end and then drill and ream the
center-hole by using the lathe itself. Hermaphrodite dividers are useful
for finding the center, as illustrated at _A_, Fig. 25, but if the work
is fairly round, a center-square _B_ is preferable. A line is scribed
across the end and then another line at right angles to the first by
changing the position of the square; the intersection of these two lines
will be the center, which should be marked by striking a pointed punch
_C_ with a hammer. If a cup or bell center-punch _D_ is available, it
will not be necessary to first make center lines, as the conical part
shown locates the punch in a central position. This style of punch
should only be used on work which is fairly round.
[Illustration: Fig. 25. Centering End with Punch preparatory to
Drilling]
After small centers have been located in both ends, their position can
be tested by placing the work between the lathe centers and rotating it
rapidly by drawing the hand quickly across it. By holding a piece of
chalk close to the work as it spins around, a mark will be made on the
"high" side if the centers are not accurate; the centers are then
shifted toward these marks. If the work is close to the finished
diameter, the centers should, of course, be located quite accurately in
order that the entire surface of the work will be turned true when it is
reduced to the finished size.
One method of forming these center-holes is indicated in Fig. 26. A
chuck _C_ is screwed onto the spindle in place of the faceplate, and a
combination center drill and reamer _R_ is gripped by the chuck jaws and
set to run true. The center is then drilled and reamed at one end by
pressing the work against the revolving drill with the tailstock
spindle, which is fed out by turning handle _n_. The piece is then
reversed for drilling the opposite end. The work may be kept from
revolving while the centers are being drilled and reamed, by attaching a
dog to it close to the tailstock end and then adjusting the cross-slide
until the dog rests upon the slide. Many parts can be held by simply
gripping them with one hand. From the foregoing it will be seen that the
small centers made by punch _C_, Fig. 25, serve as a starting point for
the drill and also as a support for the outer end of the work while the
first hole is being drilled.
[Illustration: Fig. 26. Drilling Centers in the Lathe]
The form of center-hole produced by a combination drill and reamer is
shown by the lower left-hand view in Fig. 27. A small straight hole a in
the bottom prevents the point of the lathe center from coming in contact
with the work and insures a good bearing on the conical surface _c_. The
standard angle for lathe centers is sixty degrees, as the illustration
shows, and the tapering part of all center-holes should be made to this
angle.
[Illustration: Fig. 27. Centers of Incorrect and Correct Form]
[Illustration: Fig. 28. Special Machine for Centering Parts to be
Turned]
=Centering Machine.=--Many shops have a special machine for forming
centers which enables the operation to be performed quickly. One type
of centering machine is shown in Fig. 28. The work is gripped in a chuck
_C_ that automatically locates it in a central position so that it is
not necessary to lay out the end before drilling. There are two spindles
_s_, one of which holds the drill and the other the countersink, and
these are rotated by a belt passing over pulley _P_. Each of these
spindles is advanced by lever _L_ and either of them can be moved to a
position central with the work, as they are mounted in a swiveling
frame. In operating this machine, a small straight hole is first made by
a twist drill held in one of the spindles; the other spindle is then
moved over to the center and the hole is reamed tapering. The
arrangement is such that neither spindle can be advanced by the feeding
lever except when in a central position. The amount that each spindle
can be advanced is limited by a fixed collar inside the head, and there
is also a swinging adjustable stop against which the end of the work
should be placed before tightening the chuck. These two features make it
possible to ream center holes of the same size or depth in any number of
pieces.
[Illustration: Fig. 29. The Imperfect Center Bearing is the Result of
Centering before Straightening]
=Different Forms of Centers.=--In some poorly equipped shops it is
necessary to form centers by the use of a center-punch only, as there is
no better tool. If the end of the punch has a sixty-degree taper, a fair
center can be formed in this way, but it is not a method to be
recommended, especially when accurate work is required. Sometimes
centers are made with punches that are too blunt, producing a shallow
center, such as the one shown in the upper left-hand view, Fig. 27. In
this case all the bearing is on the point of the lathe center, which is
the worst possible place for it. Another way is to simply drill a
straight hole as in the upper view to the right; this is also bad
practice in more than one respect. The lower view to the right shows a
form of center which is often found in the ends of lathe arbors, the
mouth of the center being rounded, at _r_, and the arbor end recessed as
shown. The rounded corner prevents the point of the lathe center from
catching when it is moved rapidly towards work which is not being held
quite centrally (as shown by the illustration), and the end is recessed
to protect the center against bruises. Stock that is bent should always
be straightened before the centers are drilled and reamed. If the work
is first centered and then straightened the bearing on the lathe center
would be as shown in Fig. 29. The center will then wear unevenly with
the result that the surfaces last turned will not be concentric with
those which were finished first.
[Illustration: Fig. 30. Tool Steel should be centered Concentric, in
order to remove the Decarbonized Outer Surface]
=Precaution When Centering Tool Steel.=--Ordinarily centers are so
located that the stock runs approximately true before being turned, but
when centering tool steel to be used in making tools, such as reamers,
mills, etc., which need to be hardened, particular care should be taken
to have the rough surface run fairly true. This is not merely to insure
that the piece will "true-up," as there is a more important
consideration, the disregard of which often affects the quality of the
finished tool. As is well known, the degree of hardness of a piece of
tool steel that has been heated and then suddenly cooled depends upon
the amount of carbon that it contains, steel that is high in carbon
becoming much harder than that which contains less carbon. Furthermore,
the amount of carbon found at the surface, and to some little depth
below the surface of a bar of steel, is less than the carbon content in
the rest of the bar. This is illustrated diagrammatically in Fig. 30 by
the shaded area in the view to the left. (This decarbonization is
probably due to the action of the oxygen of the air on the bar during
the process of manufacture.) If stock for a reamer is so centered that
the tool removes the decarbonized surface only on one side, as
illustrated to the right, evidently when the reamer is finished and
hardened the teeth on the side _A_ will be harder than those on the
opposite side, which would not have been the case if the rough bar had
been centered true. To avoid any trouble of this kind, stock that is to
be used for hardened tools should be enough larger than the finished
diameter and so centered that this decarbonized surface will be entirely
removed in turning.
[Illustration: Fig. 31. Three Methods of Facing the Ends Square]
=Facing the Ends of Centered Stock.=--As a piece of work is not properly
centered until the ends are faced square, we will consider this
operation in connection with centering. Some machinists prefer lathe
centers that are cut away as shown at _A_, Fig. 31, so that the point of
the side tool can be fed in far enough to face the end right up to the
center hole. Others, instead of using a special center, simply loosen
the regular one slightly and then, with the tool in a position as at
_B_, face the projecting teat by feeding both tool and center inward as
shown by the arrow. Whenever this method is employed, care should be
taken to remove any chips from the center hole which may have entered. A
method which makes it unnecessary to loosen the regular center, or to
use a special one, is to provide clearance for the tool-point by
grinding it to an angle of approximately forty-five degrees, as shown at
_C_. If the tool is not set too high, it can then be fed right up to the
lathe center and the end squared without difficulty. As for the special
center _A_, the use of special tools and appliances should always be
avoided unless they effect a saving in time or their use makes it
possible to accomplish the same end with less work.
=Truing Lathe Centers.=--The lathe centers should receive careful
attention especially when accurate work must be turned. If the headstock
center does not run true as it revolves with the work, a round surface
may be turned, but if the position of the driving dog with reference to
the faceplate is changed, the turned surface will not run true because
the turned surface is not true with the work centers. Furthermore, if
it is necessary to reverse the work for finishing the dogged or driving
end, the last part turned will be eccentric to the first. Therefore, the
lathe centers should be kept true in order to produce turned surfaces
that are true or concentric with the centered ends, as it is often
necessary to change the part being turned "end for end" for finishing,
and any eccentricity between the different surfaces would, in many
cases, spoil the work.
[Illustration: Fig. 32. Grinder for Truing Lathe Centers]
Some lathes are equipped with hardened centers in both the head-and
tailstock and others have only one hardened center which is in the
tailstock. The object in having a soft or unhardened headstock center is
to permit its being trued by turning, but as a soft center is quite
easily bruised and requires truing oftener than one that is hard, it is
better to have both centers hardened. Special grinders are used for
truing these hardened centers. One type that is very simple and easily
applied to a lathe is shown in Fig. 32. This grinder is held in the
lathe toolpost and is driven by a wheel _A_ that is held in contact with
the cone-pulley. The emery wheel _B_ is moved to a position for grinding
by adjusting the carriage and cross-slide, and it is traversed across
the conical surface of the center by handle _C_. As the grinding
proceeds, the wheel is fed inward slightly by manipulating the
cross-slide.
This grinder is set to the proper angle by placing the two centered ends
_D_ and _D_{1}_ between the lathe centers, which should be aligned as
for straight turning. The grinding spindle will then be 30 degrees from
the axis of the lathe spindle. The grinder should be carefully clamped
in the toolpost so that it will remain as located by the centered ends.
After the tailstock center is withdrawn, the emery wheel is adjusted for
grinding. As the wheel spindle is 30 degrees from the axis of the lathe
spindle, the lathe center is not only ground true but to an included
angle of 60 degrees, which is the standard angle for lathe centers.
There are many other styles of center grinders on the market, some of
which are driven by a small belt from the cone-pulley and others by
electric motors which are connected with ordinary lighting circuits. The
tailstock center is ground by inserting it in the spindle in place of
the headstock center. Before a center is replaced in its spindle, the
hole should be perfectly clean as even a small particle of dirt may
affect the alignment. The center in the headstock is usually referred to
as the "live center" because it turns around when the lathe is in use,
and the center in the tailstock as the "dead center," because it remains
stationary.
=Universal, Independent and Combination Chucks.=--Many parts that are
turned in the lathe are so shaped that they cannot be held between the
lathe centers like shafts and other similar pieces and it is often
necessary to hold them in a chuck _A_, Fig. 33, which is screwed onto
the lathe spindle instead of the faceplate. The work is gripped by the
jaws _J_ which can be moved in or out to accommodate various diameters.
There are three classes of chucks ordinarily used on the lathe, known as
the independent, universal and combination types. The independent chuck
is so named because each jaw can be adjusted in or out independently of
the others by turning the jaw screws S with a wrench. The jaws of the
universal chuck all move together and keep the same distance from the
center, and they can be adjusted by turning any one of the screws _S_,
whereas with the independent type the chuck wrench must be applied to
each jaw screw. The combination chuck, as the name implies, may be
changed to operate either as an independent or universal type. The
advantage of the universal chuck is that round and other parts of a
uniform shape are located in a central position for turning without any
adjustment. The independent type is, however, preferable in some
respects as it is usually stronger and adapted for holding odd-shaped
pieces because each jaw can be set to any required position.
[Illustration: Fig. 33. (A) Lathe Chuck. (B) Faceplate Jaw]
=Application of Chucks.=--As an example of chuck work, we shall assume
that the sides of disk _D_, Fig. 34, are to be turned flat and parallel
with each other and that an independent chuck is to be used. First the
chuck is screwed onto the lathe spindle after removing the faceplate.
The chuck jaws are then moved out or in, as the case may be, far enough
to receive the disk and each jaw is set about the same distance from the
center by the aid of concentric circles on the face of the chuck. The
jaws are then tightened while the disk is held back against them to
bring the rough inner surface in a vertical plane. If the work is quite
heavy, it can be held against the chuck, before the jaws are tightened,
by inserting a piece of wood between it and the tailstock center; the
latter is then run out far enough to force the work back. The outside
or periphery of the disk should run nearly true and it may be necessary
to move the jaws in on one side and out on the other to bring the disk
to a central position. To test its location, the lathe is run at a
moderate speed and a piece of chalk is held near the outer surface. If
the latter runs out, the "high" side will be marked by the chalk, and
this mark can be used as a guide in adjusting the jaws. It should be
remembered that the jaws are moved only one-half the amount that the
work runs out.
[Illustration: Fig. 34. (A) Radial Facing. (B) Boring Pulley Held in
Chuck]
A round-nosed tool _t_ of the shape shown can be used for radial facing
or turning operations of the kind illustrated. This tool is similar to
the form used when turning between centers, the principal difference
being in the direction of the top slope. The radial facing tool should
be ground to slope downward toward _a_ (see Fig. 35) whereas the regular
turning tool slopes toward _b_, the inclination in each case being away
from that part of the cutting edge which does the work. The cutting edge
should be the same height as the lathe centers, and the cut is taken by
feeding the tool from the outside in to the center. The cut is started
by hand and then the power feed is engaged, except for small surfaces.
The first cut should, if possible, be deep enough to get beneath the
scale, especially if turning cast iron, as a tool which just grazes the
hard outer surface will be dulled in a comparatively short time.
If it were simply necessary to turn a true flat surface and the
thickness of the disk were immaterial, two cuts would be sufficient,
unless the surface were very uneven, the first or roughing cut being
followed by a light finishing cut. For a finishing cut, the same tool
could be used, but if there were a number of disks to be faced, a
square-nosed tool _F_, Fig. 35, could probably be used to better
advantage. This type has a broad flat cutting edge that is set parallel
with the rough-turned surface and this broad edge enables a coarse feed
to be taken, thus reducing the time required for the finishing cut. If a
coarse feed were taken with the round tool, the turned surface would
have spiral grooves in it, whereas with the broad cutting edge, a smooth
surface is obtained even though the feed is coarse. The amount of feed
per revolution of the work, however, should always be less than the
width _w_ of the cutting edge. Very often broad tools cannot be used for
finishing cuts, especially when turning steel, because their greater
contact causes chattering and results in a rough surface. An old and
worn lathe is more liable to chatter than one that is heavy and
well-built, and as the diameter of the work also makes a difference, a
broad tool cannot always be used for finishing, even though,
theoretically, it would be preferable. After one side of the disk is
finished, it is reversed in the chuck, the finished surface being placed
against the jaws. The remaining rough side is then turned, care being
taken when starting the first cut to caliper the width of the disk at
several points to make sure that the two sides are parallel.
[Illustration: Fig. 35. Tools Ground so that Top Slopes away from
Working Part of Cutting Edge]
=Example of Boring.=--Another example of chuck work is shown at _B_,
Fig. 34. In this case a cast-iron pulley is to have a true hole _h_
bored through the hub. (The finishing of internal cylindrical surfaces
in a lathe is referred to as boring rather than turning.) The casting
should be set true by the rim instead of by the rough-cored hole in the
hub; this can be done by the use of chalk as previously explained. Even
though a universal type of chuck were used, the jaws of which, as will
be recalled, are self-centering, it might be necessary to turn the
pulley relative to the chuck as a casting sometimes runs out because of
rough spots or lumps which happen to come beneath one or more of the
jaws.
[Illustration: Fig. 36. Boring Tool]
The shape of tool _t_ for boring is quite different from one used for
outside turning, as shown by Fig. 36. The cutting end of a solid type of
tool is forged approximately at right angles to the body or shank, and
the top surface is ground to slope away from the working part _w_ of the
cutting edge, as with practically all turning tools. The front part or
flank, _f_ is also ground away to give the edge clearance. This type of
tool is clamped in the toolpost with the body about parallel with the
lathe spindle, and ordinarily the cutting edge would be about as high as
the center of the hole, or a little below, if anything. When starting a
cut, the tool is brought up to the work by moving the carriage and it is
then adjusted radially to get the right depth of cut, by shifting the
cross-slide. The power feed for the carriage is then used, the tool
feeding back through the hole as indicated by the arrow, Fig. 34. In
this case, as with all turning operations, the first cut should be deep
enough to remove the hard outer scale at every part of the hole. Usually
a rough-cored hole is so much smaller than the finished size that
several cuts are necessary; in any case, the last or finishing cut
should be very light to prevent the tool from springing away from the
work, so that the hole will be as true as possible. Boring tools,
particularly for small holes, are not as rigid as those used for outside
turning, as the tool has to be small enough to enter the hole and for
this reason comparatively light cuts have to be taken. When boring a
small hole, the largest tool that will enter it without interference
should be used to get the greatest rigidity possible.
[Illustration: Fig. 37 (A) Setting Outside Calipers. (B) Transferring
Measurements to Inside Calipers. (C) Micrometer Gage]
=Measuring Bored Holes.=--The diameters of small holes that are being
bored are usually measured with inside calipers or standard gages. If
the pulley were being bored to fit over some shaft, the diameter of the
shaft would first be measured by using outside calipers, as shown at
_A_, Fig. 37, the measuring points of the calipers being adjusted until
they just made contact with the shaft when passed over it. The inside
calipers are then set as at _B_ to correspond with the size of the
shaft, and the hole is bored just large enough to admit the inside
calipers easily. Very accurate measurements can be made with calipers,
but to become expert in their use requires experience. Some mechanics
never become proficient in the art of calipering because their hands are
"heavy" and they lack the sensitiveness and delicacy of touch that is
necessary. For large holes, a gage _C_ is often used, the length _l_
being adjusted to the diameter desired. Small holes are often bored to
fit hardened steel plug gages (Fig. 38), the cylindrical measuring ends
of which are made with great accuracy to standard sizes. This type of
gage is particularly useful when a number of holes have to be bored to
the same size, all holes being made just large enough to fit the gage
without any perceptible play.
[Illustration: Fig. 38. Standard Plug Gage]
_Setting Work in the Chuck._--When setting a part in a chuck, care
should be taken to so locate it that every surface to be turned will be
true when machined to the finished size. As a simple illustration, let
us assume that the hole through the cast-iron disk, Fig. 39, has been
cored considerably out of center, as shown. If the work is set by the
outside surface _S_, as it would be ordinarily, the hole is so much out
of center that it will not be true when bored to the finished size, as
indicated by the dotted lines. On the other hand, if the rough hole is
set true, the outside cannot be finished all over, without making the
diameter too small, when it is finally turned. In such a case, the
casting should be shifted, as shown by the arrow, to divide the error
between the two surfaces, both of which can then be turned as shown by
the dotted lines in the view to the right. This principle of dividing
the error when setting work can often be applied in connection with
turning and boring. After a casting or other part has been set true by
the most important surface, all other surfaces which require machining
should be tested to make sure that they all can be finished to the
proper size.
=Inaccuracy from Pressure of Chuck Jaws.=--Work that is held in a chuck
is sometimes sprung out of shape by the pressure of the chuck jaws so
that when the part is bored or turned, the finished surfaces are untrue
after the jaws are released and the work has resumed its normal shape.
This applies more particularly to frail parts, such as rings, thin
cylindrical parts, etc. Occasionally the distortion can be prevented by
so locating the work with relation to the chuck jaws that the latter
bear against a rigid part. When the work cannot be held tightly enough
for the roughing cuts without springing it, the jaws should be released
somewhat before taking the finishing cut, to permit the part to spring
back to its natural shape.
[Illustration: Fig. 39. Diagram Illustrating Importance of Setting Work
with Reference to Surfaces to be Turned]
[Illustration: Fig. 40. Drilling in the Lathe]
=Drilling and Reaming.=--When a hole is to be bored from the solid, it
is necessary to drill a hole before a boring tool can be used. One
method of drilling in the lathe is to insert an ordinary twist drill in
a holder or socket _S_, Fig. 40, which is inserted in the tailstock
spindle in place of the center. The drill is then fed through the work
by turning the handle _n_ and feeding the spindle outward as shown by
the arrow. Before beginning to drill, it is well to turn a conical spot
or center for the drill point so the latter will start true. This is
often done by using a special tool having a point like a flat drill.
This tool is clamped in the toolpost with the point at the same height
as the lathe centers. It is then fed against the center of the work and
a conical center is turned. If the drill were not given this true
starting point, it probably would enter the work more or less off
center. Drills can also be started without turning a center by bringing
the square end or butt of a tool-shank held in the toolpost in contact
with the drill near the cutting end. If the point starts off center,
thus causing the drill to wobble, the stationary tool-shank will
gradually force or bump it over to the center.
[Illustration: Fig. 41. Flat Drill and Holder]
Small holes are often finished in the lathe by drilling and reaming
without the use of a boring tool. The form of drill that is used quite
extensively for drilling cored holes in castings is shown in Fig. 41, at
_A_. This drill is flat and the right end has a large center hole for
receiving the center of the tailstock. To prevent the drill from
turning, a holder _B_, having a slot _s_ in its end through which the
drill passes, is clamped in the toolpost, as at _C_. This slot should be
set central with the lathe centers, and the drill, when being started,
should be held tightly in the slot by turning or twisting it with a
wrench as indicated in the end view at _D_; this steadies the drill and
causes it to start fairly true even though the cored hole runs out
considerably.
Another style of tool for enlarging cored holes is shown in Fig. 42, at
_A_. This is a rose chucking reamer, having beveled cutting edges on the
end and a cylindrical body, which fits closely in the reamed hole, thus
supporting and guiding the cutting end. The reamer shown at _B_ is a
fluted type with cutting edges that extend from _a_ to _b_; it is used
for finishing holes and the drill or rose reamer preceding it should
leave the hole very close to the required size. These reamers are held
while in use in a socket inserted in the tailstock spindle, as when
using a twist drill.
[Illustration: Fig. 42. Rose and Fluted Reamers]
=Holding Work on Faceplate.=--Some castings or forgings are so shaped
that they cannot be held in a chuck very well, or perhaps not at all,
and work of this kind is often clamped to a faceplate which is usually
larger than the faceplate used for driving parts that are turned between
the centers. An example of faceplate work is shown in Fig. 43. This is a
rectangular-shaped casting having a round boss or projection, the end
_e_ of which is to be turned parallel with the back face of the casting
previously finished on a planer. A rough cored hole through the center
of the boss also needs to be bored true.
The best way to perform this operation in the lathe would be to clamp
the finished surface of the casting directly against the faceplate by
bolts and clamps _a_, _b_, _c_, and _d_, as shown; the work would then
be turned just as though it were held in a chuck. By holding the casting
in this way, face _e_ will be finished parallel with the back surface
because the latter is clamped directly against the true-running surface
of the faceplate. If a casting of this shape were small enough it could
also be held in the jaws of an independent chuck, but if the surface e
needs to be exactly parallel with the back face, it is better to clamp
the work to the faceplate. Most lathes have two faceplates: One of small
diameter used principally for driving work turned between centers, and a
large one for holding heavy or irregularly shaped pieces; either of
these can be screwed onto the spindle, and the large faceplate has a
number of slots through which clamping bolts can be inserted.
[Illustration: Fig. 43. Casting Clamped to Faceplate for Turning and
Boring]
The proper way to clamp a piece to the faceplate depends, of course,
largely on its shape and the location of the surface to be machined, but
in any case it is necessary to hold it securely to prevent any shifting
after a cut is started. Sometimes castings can be held by inserting
bolts through previously drilled holes, but when clamps are used in
connection with the bolts, their outer ends are supported by hardwood or
metal blocks which should be just high enough to make the clamp bear
evenly on the work. When deep roughing cuts have to be taken,
especially on large diameters, it is well to bolt a piece to the
faceplate and against one side of the casting, as at _D_, to act as a
driver and prevent the work from shifting; but a driver would not be
needed in this particular case. Of course a faceplate driver is always
placed to the rear, as determined by the direction of rotation, because
the work tends to shift backward when a cut is being taken. If the
surface which is clamped against the faceplate is finished as in this
case, the work will be less likely to shift if a piece of paper is
placed between it and the faceplate.
[Illustration: Fig. 44. Cast Elbow held on Angle-plate attached to
Faceplate]
Work mounted on the faceplate is generally set true by some surface
before turning. As the hole in this casting should be true with the
round boss, the casting is shifted on the faceplate until the rough
outer surface of the boss runs true; the clamps which were previously
set up lightly are then tightened. The face e is first turned by using a
round-nosed tool. This tool is then replaced by a boring tool and the
hole is finished to the required diameter. If the hole being bored is
larger than the central hole in the faceplate, the casting should be
clamped against parallel pieces, and not directly against the faceplate,
to provide clearance for the tool when it reaches the inner end of the
hole and prevent it from cutting the faceplate. The parallel pieces
should be of the same thickness and be located near the clamps to
prevent springing the casting.
=Application of Angle-plate to Faceplate.=--Another example of faceplate
work is shown in Fig. 44. This is a cast-iron elbow _E_, the two flanges
of which are to be faced true and square with each other. The shape of
this casting is such that it would be very difficult to clamp it
directly to the faceplate, but it is easily held on an angle-plate _P_,
which is bolted to the faceplate. The two surfaces of this angle-plate
are square with each other so that when one flange of the elbow is
finished and bolted against the angle-plate, the other will be faced
square. When setting up an angle-plate for work of this kind, the
distance from its work-holding side to the center of the faceplate is
made equal to the distance _d_ between the center of one flange and the
face of the other, so that the flange to be faced will run about true
when bolted in place. As the angle-plate and work are almost entirely on
one side of the faceplate, a weight _W_ is attached to the opposite side
for counterbalancing. Very often weights are also needed to
counterbalance offset parts that are bolted directly to the faceplate.
The necessity of counterbalancing depends somewhat upon the speed to be
used for turning. If the surface to be machined is small in diameter so
that the lathe can be run quite rapidly, any unbalanced part should
always be counterbalanced.
Sometimes it is rather difficult to hold heavy pieces against the
vertical surface of the faceplate while applying the clamps, and
occasionally the faceplate is removed and placed in a horizontal
position on the bench; the work can then be located about right, and
after it is clamped, the faceplate is placed on the lathe spindle by the
assistance of a crane.
Special faceplate jaws, such as the one shown to the right in Fig. 33,
can often be used to advantage for holding work on large faceplates.
Three or four of these jaws are bolted to the faceplate which is
converted into a kind of independent chuck. These faceplate jaws are
especially useful for holding irregularly shaped parts, as the different
jaws can be located in any position.
=Supporting Outer End of Chucked Work.=--Fig. 45 shows how the tailstock
center is sometimes used for supporting the outer end of a long casting,
the opposite end of which is held in a chuck. This particular casting
is to be turned and bored to make a lining for the cylinder of a
locomotive in order to reduce the diameter of the cylinder which has
been considerably enlarged by re-boring a number of times. These
bushings are rough-turned on the outside while the outer end is
supported by the cross-shaped piece or "spider" which forms a
center-bearing for the tailstock. This spider has set screws in the
flanged ends of the arms, which are tightened against the inner surface
of the casting and are adjusted one way or the other in order to locate
it in a concentric position. After roughing the outside, the inside is
bored to the finish size; then centered disks, which fit into the bore,
are placed in the ends of the bushing and the latter is finish-turned.
The object in rough turning the outside prior to boring is to avoid the
distortion which might occur if this hard outer surface were removed
last.
[Illustration: Fig. 45. Rough Turning a Cylinder Lining--Note Method of
Supporting Outer End]
=Boring Large Castings in the Lathe.=--An ordinary engine lathe is
sometimes used for boring engine or pump cylinders, linings, etc., which
are too large to be held in the chuck or on a faceplate, and must be
attached to the lathe carriage. As a rule, work of this class is done in
a special boring machine (see "Horizontal Boring Machines"), but if
such a machine is not available, it may be necessary to use a lathe.
There are two general methods of boring.
Fig. 46 shows how the lining illustrated in Fig. 45 is bored in a large
engine lathe. The casting is held in special fixtures which are attached
to the lathe carriage, and the boring-bar is rotated by the lathe
spindle. The tool-head of this boring-bar carries two tools located 180
degrees apart and it is fed along the bar by a star-feed mechanism shown
attached to the bar and the tailstock spindle. Each time the bar
revolves, the star wheel strikes a stationary pin and turns the
feed-screw which, as the illustration shows, extends along a groove cut
in one side of the bar. This feed-screw passes through a nut attached to
the tool-head so that the latter is slowly fed through the bore. When
using a bar of this type, the carriage, of course, remains stationary.
[Illustration: Fig. 46. Boring a Cylinder Lining in an Ordinary Engine
Lathe]
Cylindrical parts attached to the carriage can also be bored by using a
plain solid bar mounted between the centers. The bar must be provided
with a cutter for small holes or a tool-head for larger diameters
(preferably holding two or more tools) and the boring is done by
feeding the carriage along the bed by using the regular power feed of
the lathe. A symmetrically shaped casting like a bushing or lining is
often held upon wooden blocks bolted across the carriage. These are
first cut away to form a circular seat of the required radius, by using
the boring-bar and a special tool having a thin curved edge. The casting
is then clamped upon these blocks by the use of straps and bolts, and if
the curved seats were cut to the correct radius, the work will be
located concentric with the boring-bar. When using a boring-bar of this
type, the bar must be long enough to allow the part being bored to feed
from one side of the cutter-head to the other, the cutter-head being
approximately in a central location.
[Illustration: Fig. 47. Method of Setting Circle on Work Concentric with
Lathe Spindle]
=Boring Holes to a Given Center Distance.=--In connection with faceplate
work, it is often necessary to bore two or more holes at a given
distance apart. The best method of doing this may depend upon the
accuracy required. For ordinary work sometimes two or more circles _A_
and _B_ (Fig. 47) are drawn upon the part to be bored, in the position
for the holes; the piece is then clamped to the faceplate and one of the
circles is centered with the lathe spindle by testing it with a pointer
C held in the toolpost; that is, when the pointer follows the circle as
the work is turned, evidently the circle is concentric with the spindle.
The hole is then drilled and bored. The other circle is then centered
in the same way for boring the second hole. As will be seen, the
accuracy of this method depends first, upon the accuracy with which the
circles were laid out, and second; upon the care taken in setting them
concentric. For a more accurate way of locating parts for boring, see
"Use of Center Indicator" and "Locating Work by the Button Method."
=Turning Brass, Bronze and Copper.=--When turning soft yellow brass, a
tool should be used having very little or no slope or rake on the top
surface against which the chip bears, and for plain cylindrical turning,
the point of the tool is drawn out quite thin and rounded, by grinding,
to a radius of about 1/8 or 3/16 inch. If a tool having very much top
slope is used for brass, there is danger of its gouging into the metal,
especially if the part being turned is at all flexible. The clearance
angle of a brass tool is usually about 12 or 14 degrees, which is 3 or 4
degrees greater than the clearance for steel turning tools. Most brass
is easily turned, as compared with steel, and for that reason this
increase in clearance is desirable, because it facilitates feeding the
tool into the metal, especially when the carriage and cross-slide
movements are being controlled by hand as when turning irregular shapes.
The speed for turning soft brass is much higher than for steel, being
ordinarily between 150 and 200 feet per minute. When turning phosphor,
tobin or other tough bronze compositions, the tool should be ground with
rake the same as for turning steel, and lard oil is sometimes used as a
lubricant. The cutting speed for bronzes varies from 35 or 40 to 80 feet
per minute, owing to the difference in the composition of bronze alloys.
Turning tools for copper are ground with a little more top rake than is
given steel turning tools, and the point should be slightly rounded. It
is important to have a keen edge, and a grindstone is recommended for
sharpening copper turning tools. Milk is generally considered the best
lubricant to use when turning copper. The speed can be nearly as fast as
for brass.
=Machining Aluminum.=--Tools for turning aluminum should have acute
cutting angles. After rough-grinding the tool, it is advisable to finish
sharpening the cutting edge on a grindstone or with an oilstone for fine
work, as a keen edge is very essential. High speeds and comparatively
light cuts are recommended. The principal difficulty in the machining of
aluminum and aluminum alloys is caused by the clogging of the chips,
especially when using such tools as counterbores and milling cutters.
This difficulty can be avoided largely by using the right kind of
cutting lubricant. Soap-water and kerosene are commonly employed. The
latter enables a fine finish to be obtained, provided the cutting tool
is properly ground.
The following information on this subject represents the experience of
the Brown-Lipe Gear Co., where aluminum parts are machined in large
quantities: For finishing bored holes, a bar equipped with cutters has
been found more practicable than reamers. The cutters used for machining
4-inch holes have a clearance of from 20 to 22 degrees and no rake or
slope on the front faces against which the chips bear. The roughing
cutters for this work have a rather sharp nose, being ground on the
point to a radius of about 3/32 inch, but for securing a smooth surface,
the finishing tools are rounded to a radius of about 3/4 inch. The
cutting speed, as well as the feed, for machining aluminum is from 50 to
60 per cent faster than the speeds and feeds for cast iron. The
lubricant used by this company is composed of one part "aqualine" and 20
parts water. This lubricant not only gives a smooth finish but preserves
a keen cutting edge and enables tools to be used much longer without
grinding. Formerly, a lubricant composed of one part of high-grade lard
oil and one part of kerosene was used. This mixture costs approximately
30 cents per gallon, whereas the aqualine and water mixture now being
used costs less than 4 cents per gallon, and has proved more effective
than the lubricant formerly employed.
CHAPTER II
LATHE TURNING TOOLS AND CUTTING SPEEDS
Notwithstanding the fact that a great variety of work can be done in the
lathe, the number of turning tools required is comparatively small. Fig.
1 shows the forms of tools that are used principally, and typical
examples of the application of these various tools are indicated in Fig.
2. The reference letters used in these two illustrations correspond for
tools of the same type, and both views should be referred to in
connection with the following description.
=Turning Tools for General Work.=--The tool shown at _A_ is the form
generally used for rough turning, that is for taking deep cuts when
considerable metal has to be removed. At _B_ a tool of the same type is
shown, having a bent end which enables it to be used close up to a
shoulder or surface _s_ that might come in contact with the tool-rest if
the straight form were employed. Tool _C_, which has a straight cutting
end, is used on certain classes of work for taking light finishing cuts,
with a coarse feed. This type of tool has a flat or straight cutting
edge at the end, and will leave a smooth finish even though the feed is
coarse, provided the cutting edge is set parallel with the tool's travel
so as to avoid ridges. Broad-nosed tools and wide feeds are better
adapted for finishing cast iron than steel. When turning steel, if the
work is at all flexible, a broad tool tends to gouge into it and for
this reason round-nosed tools and finer feeds are generally necessary. A
little experience in turning will teach more on this point than a whole
chapter on the subject.
[Illustration: Fig. 1. Set of Lathe Turning Tools for General Work]
[Illustration: Fig. 2. Views illustrating Use of Various Types of Lathe
Tools]
The side-tools shown at _D_ and _E_ are for facing the ends of shafts,
collars, etc. The first tool is known as a right side-tool because it
operates on the right end or side of a shaft or collar, whereas the left
side-tool _E_ is used on the opposite side, as shown in Fig. 2.
Side-tools are also bent to the right or left because the cutting edge
of a straight tool cannot always be located properly for facing certain
surfaces. A bent right side-tool is shown at _F_. A form of tool that is
frequently used is shown at _G_; this is known as a parting tool and is
used for severing pieces and for cutting grooves, squaring corners, etc.
The same type of tool having a bent end is shown at _H_ (Fig. 2)
severing a piece held in the chuck. Work that is held between centers
should not be entirely severed with a parting tool unless a steadyrest
is placed between the tool and faceplate, as otherwise the tool may be
broken by the springing of the work just before the piece is cut in two.
It should be noted that the sides of this tool slope inward back of the
cutting edge to provide clearance when cutting in a narrow groove.
At _I_ a thread tool is shown for cutting a U. S. standard thread. This
thread is the form most commonly used in this country at the present
time. A tool for cutting a square thread is shown at _J_. This is shaped
very much like a parting tool except that the cutting end is inclined
slightly to correspond with the helix angle of the thread, as explained
in Chapter IV, which contains descriptions of different thread forms and
methods of cutting them. Internal thread tools are shown at _K_ and _L_
for cutting U. S. standard and square threads in holes. It will be seen
that these tools are somewhat like boring tools excepting the ends which
are shaped to correspond with the thread which they are intended to cut.
[Illustration: Fig. 3. Turning Tool with Inserted Cutter]
A tool for turning brass is shown at _M_. Brass tools intended for
general work are drawn out quite thin and they are given a narrow
rounded point. The top of the brass tool is usually ground flat or
without slope as otherwise it tends to gouge into the work, especially
if the latter is at all flexible. The end of a brass tool is sometimes
ground with a straight cutting edge for turning large rigid work, such
as brass pump linings, etc., so that a coarse feed can be used without
leaving a rough surface. The tools at _N_ and _O_ are for boring or
finishing drilled or cored holes. Two sizes are shown, which are
intended for small and large holes, respectively.
The different tools referred to in the foregoing might be called the
standard types because they are the ones generally used, and as Fig. 2
indicates, they make it possible to turn an almost endless variety of
forms. Occasionally some special form of tool is needed for doing odd
jobs, having, perhaps, an end bent differently or a cutting edge shaped
to some particular form. Tools of the latter type, which are known as
"form tools," are sometimes used for finishing surfaces that are either
convex, concave, or irregular in shape. The cutting edges of these tools
are carefully filed or ground to the required shape, and the form given
the tool is reproduced in the part turned. Ornamental or other irregular
surfaces can be finished very neatly by the use of such tools. It is
very difficult, of course, to turn convex or concave surfaces with a
regular tool; in fact, it would not be possible to form a true spherical
surface, for instance, without special equipment, because the tool could
not be moved along a true curve by simply using the longitudinal and
cross feeds. Form tools should be sharpened by grinding entirely on the
top surface, as any grinding on the end or flank would alter the shape
of the tool.
[Illustration: Fig. 4. Heavy Inserted-cutter Turning Tool]
=Tool-holders with Inserted Cutters.=--All of the tools shown in Fig. 1
are forged from the bar, and when the cutting ends have been ground down
considerably it is necessary to forge a new end. To eliminate the
expense of this continual dressing of tools and also to effect a great
reduction in the amount of tool steel required, tool-holders having
small inserted cutters are used in many shops. A tool-holder of this
type, for outside turning, is shown in Fig. 3. The cutter _C_ is held in
a fixed position by the set-screw shown, and it is sharpened,
principally, by grinding the end, except when it is desired to give the
top of the cutter a different slope from that due to its angular
position. Another inserted-cutter turning tool is shown in Fig. 4, which
is a heavy type intended for roughing. The cutter in this case has teeth
on the rear side engaging with corresponding teeth cut in the clamping
block which is tightened by a set-screw on the side opposite that shown.
With this arrangement, the cutter can be adjusted upward as the top is
ground away.
[Illustration: Fig. 5. Parting Tool with Inserted Blade]
[Illustration: Fig. 6. Boring Tool with Inserted Cutter and Adjustable
Bar]
A parting tool of the inserted blade type is shown in Fig. 5. The blade
_B_ is clamped by screw _S_ and also by the spring of the holder when
the latter is clamped in the toolpost. The blade can, of course, be
moved outward when necessary. Fig. 6 shows a boring tool consisting of a
holder _H_, a bar _B_ that can be clamped in any position, and an
inserted cutter _C_. With this type of boring tool, the bar can be
extended beyond the holder just far enough to reach through the hole to
be bored, which makes the tool very rigid. A thread tool of the holder
type is shown in Fig. 7. The angular edge of the cutter _C_ is
accurately ground by the manufacturers, so that the tool is sharpened
by simply grinding it flat on the top. As the top is ground away, the
cutter is raised by turning screw _S_, which can also be used for
setting the tool to the proper height.
=The Position of Turning Tools.=--The production of accurate lathe work
depends partly on the condition of the lathe used and also on the care
and judgment exercised by the man operating it. Even though a lathe is
properly adjusted and in good condition otherwise, errors are often made
which are due to other causes which should be carefully avoided. If the
turning tool is clamped so that the cutting end extends too far from the
supporting block, the downward spring of the tool, owing to the thrust
of the cut, sometimes results in spoiled work, especially when an
attempt is made to turn close to the finished size by taking a heavy
roughing cut. Suppose the end of a cylindrical part is first reduced for
a short distance by taking several trial cuts until the diameter _d_,
Fig. 8, is slightly above the finished size and the power feed is then
engaged. When the tool begins to take the full depth _e_ of the cut, the
point, which ordinarily would be set a little above the center, tends to
spring downward into the work, and if there were considerable springing
action, the part would probably be turned below the finished size, the
increased reduction beginning at the point where the full cut started.
[Illustration: Fig. 7. Threading Tool]
This springing action, as far as the tool is concerned, can be
practically eliminated by locating the tool so that the distance _A_
between the tool-block and cutting end, or the "overhang," is as short
as possible. Even though the tool has little overhang it may tilt
downward because the toolslide is loose on its ways, and for this reason
the slide should have a snug adjustment that will permit an easy
movement without unnecessary play. The toolslides of all lathes are
provided with gibs which can be adjusted by screws to compensate for
wear, or to secure a more rigid bearing.
[Illustration: Fig. 8. To avoid springing, Overhang A of Tool should not
be Excessive]
When roughing cuts are to be taken, the tool should be located so that
any change in its position which might be caused by the pressure of the
cut will not spoil the work. This point is illustrated at _A_ in Fig. 9.
Suppose the end of a rod has been reduced by taking a number of trial
cuts, until it is 1/32 inch above the finished size. If the power feed
is then engaged with the tool clamped in an oblique position, as shown,
when the full cut is encountered at _c_, the tool, unless very tightly
clamped, may be shifted backward by the lateral thrust of the cut, as
indicated by the dotted lines. The point will then begin turning smaller
than the finished size and the work will be spoiled. To prevent any
change of position, it is good practice, especially when roughing, to
clamp the tool square with the surface being turned, or in other words,
at right angles to its direction of movement. Occasionally, however,
there is a decided advantage in having the tool set at an angle. For
example, if it is held about as shown at _B_, when turning the flange
casting _C_, the surfaces _s_ and _s_{1}_ can be finished without
changing the tool's position. Cylindrical and radial surfaces are often
turned in this way in order to avoid shifting the tool, especially when
machining parts in quantity.
=Tool Grinding.=--In the grinding of lathe tools there are three things
of importance to be considered: First, the cutting edge of the tool (as
viewed from the top) needs to be given a certain shape; second, there
must be a sufficient amount of clearance for the cutting edge; and
third, tools, with certain exceptions, are ground with a backward slope
or a side slope, or with a combination of these two slopes on that part
against which the chip bears when the tool is in use.
[Illustration: Fig. 9. (A) The Way in which Tool is sometimes displaced
by Thrust of Cut, when set at an Angle. (B) Tool Set for Finishing both
Cylindrical and Radial Surfaces]
In Fig. 10 a few of the different types of tools which are used in
connection with lathe work are shown. This illustration also indicates
the meaning of the various terms used in tool grinding. As shown, the
clearance of the tool is represented by the angle [alpha], the back
slope is represented by the angle [beta], and the side slope by the
angle [gamma]. The angle [delta] for a tool without side slope is known
as the lip angle or the angle of keenness. When, however, the tool has
both back and side slopes, this lip angle would more properly be the
angle between the flank _f_ and the top of the tool, measured diagonally
along a line _z--z_. It will be seen that the lines _A--B_ and _A--C_
from which the angles of clearance and back slope are measured are
parallel with the top and sides of the tool shank, respectively. For
lathe tools, however, these lines are not necessarily located in this
way when the tool is in use, as the height of the tool point with
relation to the work center determines the position of these lines, so
that the _effective_ angles of back slope, clearance and keenness are
changed as the tool point is lowered or raised. The way the position of
the tool affects these angles will be explained later.
[Illustration: Fig. 10. Illustration showing the Meaning of Terms used
in Tool Grinding as applied to Tools of Different Types]
While tools must, of necessity, be varied considerably in shape to adapt
them to various purposes, there are certain underlying principles
governing their shape which apply generally; so in what follows we shall
not attempt to explain in detail just what the form of each tool used on
the lathe should be, as it is more important to understand how the
cutting action of the tool and its efficiency is affected when it is
improperly ground. When the principle is understood, the grinding of
tools of various types and shapes is comparatively easy.
[Illustration: Fig. 11. Plan View of Lathe Turning and Threading Tools]
=Shape or Contour of Cutting Edge.=--In the first place we shall
consider the shape or contour of the cutting edge of the tool as viewed
from the top, and then take up the question of clearance and slope, the
different elements being considered separately to avoid confusion. The
contour of the cutting edge depends primarily upon the purpose for which
the tool is intended. For example, the tool _A_, in Fig. 11, where a
plan view of a number of different lathe tools is shown, has a very
different shape from that of, say, tool _D_, as the first tool is used
for rough turning, while tool _D_ is intended for cutting grooves or
severing a turned part. Similarly, tool _E_ is V-shaped because it is
used for cutting V-threads. Tools _A_, _B_ and _C_, however, are regular
turning tools; that is, they are all intended for turning plain
cylindrical surfaces, but the contour of the cutting edges varies
considerably, as shown. In this case it is the characteristics of the
work and the cut that are the factors which determine the shape. To
illustrate, tool _A_ is of a shape suitable for rough-turning large and
rigid work, while tool _B_ is adapted for smaller and more flexible
parts. The first tool is well shaped for roughing because experiments
have shown that a cutting edge of a large radius is capable of higher
cutting speed than could be used with a tool like _B_, which has a
smaller point. This increase in the cutting speed is due to the fact
that the tool _A_ removes a thinner chip for a given feed than tool _B_;
therefore, the speed may be increased without injuring the cutting edge
to the same extent. If, however, tool _A_ were to be used for turning a
long and flexible part, chattering might result; consequently, a tool
_B_ having a point with a smaller radius would be preferable, if not
absolutely necessary.
The character of the work also affects the shape of tools. The tool
shown at _C_ is used for taking light finishing cuts with a wide feed.
Obviously, if the straight or flat part of the cutting edge is in line
with the travel of the tool, the cut will be smooth and free from
ridges, even though the feed is coarse, and by using a coarse feed the
cut is taken in less time; but such a tool cannot be used on work that
is not rigid, as chattering would result. Therefore, a smaller cutting
point and a reduced feed would have to be employed. Tools with broad
flat cutting edges and coarse feeds are often used for taking finishing
cuts in cast iron, as this metal offers less resistance to cutting than
steel, and is less conducive to chattering.
The shape of a tool (as viewed from the top) which is intended for a
more specific purpose than regular turning, can be largely determined by
simply considering the tool under working conditions. This point may be
illustrated by the parting tool _D_ which, as previously stated, is used
for cutting grooves, squaring corners, etc. Evidently this tool should
be widest at the cutting edge; that is, the sides _d_ should have a
slight amount of clearance so that they will not bind as the tool is fed
into a groove. As the tool at _E_ is for cutting a V-thread, the angle
[alpha] between its cutting edges must equal the angle between the sides
of a V-thread, or 60 degrees. The tool illustrated at _F_ is for cutting
inside square threads. In this case the width _w_ should be made equal
to one-half the pitch of the thread (or slightly greater to provide
clearance for the screw), and the sides should be given a slight amount
of side clearance, the same as with the parting tool _D_. So we see that
the outline of the tool, as viewed from the top, must conform to and be
governed by its use.
=Direction of Top Slope for Turning Tools.=--Aside from the question of
the shape of the cutting edge as viewed from the top, there remains to
be determined the amount of clearance that the tool shall have, and also
the slope (and its direction) of the top of the tool. By the top is
meant that surface against which the chip bears while it is being
severed. It may be stated, in a general way, that the direction in which
the top of the tool should slope should be away from what is to be the
_working part_ of the cutting edge. For example, the working edge of a
roughing tool _A_ (Fig. 11), which is used for heavy cuts, would be,
practically speaking, between points _a_ and _b_, or, in other words,
most of the work would be done by this part of the cutting edge;
therefore the top should slope back from this part of the edge.
Obviously, a tool ground in this way will have both a back and a side
slope.
When most of the work is done on the point or nose of the tool, as, for
example, with the lathe finishing tool _C_ which takes light cuts, the
slope should be straight back from the point or cutting edge _a--b_. As
the side tool shown in Fig. 10 does its cutting along the edge _a--b_,
the top is given a slope back from this edge as shown in the end view.
This point should be remembered, for when the top slopes in the right
direction, less power is required for cutting. Tools for certain classes
of work, such as thread tools, or those for turning brass or chilled
iron, are ground flat on top, that is, without back or side slope.
=Clearance for the Cutting Edge.=--In order that the cutting edge may
work without interference, it must have clearance; that is, the flank
_f_ (Fig. 10) must be ground to a certain angle [alpha] so that it will
not rub against the work and prevent the cutting edge from entering the
metal. This clearance should be just enough to permit the tool to cut
freely. A clearance angle of eight or ten degrees is about right for
lathe turning tools.
The back slope of a tool is measured from a line _A--B_ which is
parallel to the shank, and the clearance angle, from a line _A--C_ at
right angles to line _A--B_. These lines do not, however, always occupy
this position with relation to the tool shank when the tool is in use.
As shown to the left in Fig. 12, the base line _A--B_ for a turning
tool in use intersects with the point of the tool and center of the
work, while the line _A--C_ remains at right angles to the first. It
will be seen, then, that by raising the tool, as shown to the right, the
_effective_ clearance angle [alpha] will be diminished, whereas lowering
it, as shown by the dotted lines, will have the opposite effect.
A turning tool for brass or other soft metal, particularly where
considerable hand manipulation is required, could advantageously have a
clearance of twelve or fourteen degrees, as it would then be easier to
feed the tool into the metal; but, generally speaking, the clearance for
turning tools should be just enough to permit them to cut freely.
Excessive clearance weakens the cutting edge and may cause it to crumble
under the pressure of the cut.
[Illustration: Fig. 12. Illustrations showing how Effective Angles of
Slope and Clearance change as Tool is raised or lowered]
=Angle of Tool-point and Amount of Top Slope.=--The lip angle or the
angle of keenness [delta] (Fig. 10) is another important consideration
in connection with tool grinding, for it is upon this angle that the
efficiency of the tool largely depends. By referring to the illustration
it will be seen that this angle is governed by the clearance and the
slope [beta], and as the clearance remains practically the same, it is
the slope which is varied to meet different conditions. Now, the amount
of slope a tool should have depends on the work for which it is
intended. If, for example, a turning tool is to be used for roughing
medium or soft steel, it should have a back slope of about eight degrees
and a side slope ranging from fourteen to twenty degrees, while a tool
for cutting very hard steel should have a back slope of about five
degrees and a side slope of nine degrees.
[Illustration: Fig. 13. (A) Blunt Tool for Turning Hard Steel. (B)
Tool-point Ground to give Keenness]
The reason for decreasing the slope and thus increasing the lip angle
for harder metals is to give the necessary increased strength to the
cutting edge to prevent it from crumbling under the pressure of the cut.
The tool illustrated at _A_, Fig. 13, is much stronger than it would be
if ground as shown at _B_, as the former is more blunt. If a tool ground
as at _A_, however, were used for cutting very soft steel, there would
be a greater chip pressure on the top and, consequently, a greater
resistance to cutting, than if a keener tool had been employed;
furthermore the cutting speed would have to be lower, which is of even
greater importance than the chip pressure; therefore, the lip angle, as
a general rule, should be as small as possible without weakening the
tool so that it cannot do the required work. In order to secure a strong
and well-supported cutting edge, tools used for turning very hard metal,
such as chilled rolls, etc., are ground with practically no slope and
with very little clearance. Brass tools, while given considerable
clearance, as previously stated, are ground flat on top or without
slope; this is not done, however, to give strength to the cutting edge,
but rather to prevent the tool from gouging into the work, which it is
likely to do if the part being turned is at all flexible and the tool
has top slope.
Experiments conducted by Mr. F. W. Taylor to determine the most
efficient form for lathe roughing tools showed that the nearer the lip
angle approached sixty-one degrees, the higher the cutting speed. This,
however, does not apply to tools for turning cast iron, as the latter
will work more efficiently with a lip angle of about sixty-eight
degrees. This is doubtless because the chip pressure, when turning cast
iron, comes closer to the cutting edge which should, therefore, be more
blunt to withstand the abrasive action and heat. Of course, the
foregoing remarks concerning lip angles apply more particularly to tools
used for roughing.
[Illustration: Fig. 14. Grinding the Top and Flank of a Turning Tool]
=Grinding a Lathe Tool.=--The way a turning tool is held while the top
surface is being ground is shown to the left in Fig. 14. By inclining
the tool with the wheel face, it will be seen that both the back and
side slopes may be ground at the same time. When grinding the flank of
the tool it should be held on the tool-rest of the emery wheel or
grindstone, as shown by the view to the right. In order to form a curved
cutting edge, the tool is turned about the face of the stone while it is
being ground. This rotary movement can be effected by supporting the
inner end of the tool with one hand while the shank is moved to and fro
with the other.
Often a tool which has been ground properly in the first place is
greatly misshapen after it has been sharpened a few times. This is
usually the result of attempts on the part of the workman to re-sharpen
it hurriedly; for example, it is easier to secure a sharp edge on the
turning tool shown to the left in Fig. 12, by grinding the flank as
indicated by the dotted line, than by grinding the entire flank. The
clearance is, however, reduced and the lip angle changed.
There is great danger when grinding a tool of burning it or drawing the
temper from the fine cutting edge, and, aside from the actual shape of
the cutting end, this is the most important point in connection with
tool grinding. If a tool is pressed hard against an emery or other
abrasive wheel, even though the latter has a copious supply of water,
the temper will sometimes be drawn. When grinding a flat surface, to
avoid burning, the tool should frequently be withdrawn from the stone so
that the cooling water (a copious supply of which should be provided)
can reach the surface being ground. A moderate pressure should also be
applied, as it is better to spend an extra minute or two in grinding
than to ruin the tool by burning, in an attempt to sharpen it quickly.
Of course, what has been said about burning applies more particularly to
carbon steel, but even self-hardening steels are not improved by being
over-heated at the stone. In some shops, tools are ground to the
theoretically correct shape in special machines instead of by hand. The
sharpened tools are then kept in the tool-room and are given out as they
are needed.
=Cutting Speeds and Feeds.=--The term cutting speed as applied to
turning operations is the speed in feet per minute of the surface being
turned, or, practically speaking, it is equivalent to the length of a
chip, in feet, which would be turned in one minute. The term cutting
speed should not be confused with revolutions per minute, because the
cutting speed depends not only upon the speed of the work but also upon
its diameter. The feed of a tool is the amount it moves across the
surface being turned for each revolution; that is, when turning a
cylindrical piece, the feed is the amount that the tool moves sidewise
for each revolution of the work. Evidently the time required for turning
is governed largely by the cutting speed, the feed, and the depth of the
cut; therefore, these elements should be carefully considered.
Cutting Speeds and Feeds for Turning Tools[1]
+---------------------------------++---------------------------------+
| Steel--Standard 7/8-inch Tool ||Cast Iron--Standard 7/8-inch Tool|
+-----+-----+---------------------++-----+-----+---------------------+
| | | Speed in Feet per || | | Speed in Feet per |
|Depth|Feed | Minute for a Tool ||Depth|Feed | Minute for a Tool |
| of | in | which is to last || of | in | which is to last |
| Cut | In- | 1-1/2 Hour before || Cut | In- | 1-1/2 Hour before |
| in |ches | Re-grinding || in |ches | Re-grinding |
| In- | +------+------+-------++ In- | +-------+------+------+
|ches | | Soft |Medium| Hard ||ches | | Soft |Medium| Hard |
| | |Steel |Steel |Steel || | | Cast | Cast | Cast |
| | | | | || | | Iron | Iron | Iron |
+-----+-----+------+------+-------++-----+-----+-------+------+------+
| | 1/64| 476 | 238 | 108 || | 1/16| 122 | 61.2 | 35.7 |
|3/32 | 1/32| 325 | 162 | 73.8 ||3/32 | 1/8 | 86.4 | 43.2 | 25.2 |
| | 1/16| 222 | 111 | 50.4 || | 3/16| 70.1 | 35.1 | 20.5 |
| | 3/32| 177 | 88.4| 40.2 ++-----+-----+-------+------+------+
+-----+-----+------+------+-------++ | 1/32| 156 | 77.8 | 45.4 |
| | 1/64| 420 | 210 | 95.5 || 1/8 | 1/16| 112 | 56.2 | 32.8 |
| 1/8 | 1/32| 286 | 143 | 65.0 || | 1/8 | 79.3 | 39.7 | 23.2 |
| | 1/16| 195 | 97.6| 44.4 || | 3/16| 64.3 | 32.2 | 18.8 |
| | 1/8 | 133 | 66.4| 30.2 ++-----+-----+-------+------+------+
+-----+-----+------+------+-------++ | 1/32| 137 | 68.6 | 40.1 |
| | 1/64| 352 | 176 | 80.0 ||3/16 | 1/16| 99.4 | 49.7 | 29.0 |
|3/16 | 1/32| 240 | 120 | 54.5 || | 1/8 | 70.1 | 35.0 | 20.5 |
| | 1/16| 164 | 82 | 37.3 || | 3/16| 56.8 | 28.4 | 16.6 |
| | 1/8 | 112 | 56 | 25.5 ++-----+-----+-------+------+------+
+-----+-----+------+------+-------++ | 1/32| 126 | 62.9 | 36.7 |
| | 1/64| 312 | 156 | 70.9 || 1/4 | 1/16| 90.8 | 45.4 | 26.5 |
| 1/4 | 1/32| 213 | 107 | 48.4 || | 1/8 | 64.1 | 32.0 | 18.7 |
| | 1/16| 145 | 72.6| 33.0 || | 3/16| 52 | 26.0 | 15.2 |
| | 3/32| 116 | 58.1| 26.4 ++-----+-----+-------+------+------+
+-----+-----+------+------+-------++ | 1/32| 111 | 55.4 | 32.3 |
| | 1/64| 264 | 132 | 60.0 || 3/8 | 1/16| 80 | 40.0 | 23.4 |
| 3/8 | 1/32| 180 | 90.2| 41.0 || | 1/8 | 56.4 | 28.2 | 16.5 |
| | 1/16| 122 | 61.1| 27.8 ++-----+-----+-------+------+------+
+-----+-----+------+------+-------++ | 1/32| 104 | 52.1 | 30.4 |
| 1/2 | 1/64| 237 | 118 | 53.8 || 1/2 | 1/16| 75.2 | 37.6 | 22.0 |
| | 1/32| 162 | 80.8| 36.7 || | 1/8 | 43.1 | 21.6 | 12.6 |
+-----+-----+------+------+-------++-----+-----+-------+------+------+
|Steel--Standard 5/8-inch Tool ||Cast Iron--Standard 5/8-inch Tool|
+-----+-----+------+------+-------++-----+-----+-------+------+------+
|Depth|Feed | Soft |Medium| Hard ||Depth|Feed | Soft |Medium| Hard |
| of | |Steel |Steel |Steel || of | | Cast | Cast | Cast |
| Cut | | | | || Cut | | Iron | Iron | Iron |
+-----+-----+------+------+-------++-----+-----+-------+------+------+
| | 1/64| 548 | 274 | 125 || | 1/32| 160 | 80.0 | 46.6 |
|1/16 | 1/32| 358 | 179 | 81.6 ||3/32 | 1/16| 110 | 55.0 | 32.2 |
| | 1/16| 235 | 117 | 53.3 || | 1/8 | 75.4 | 37.7 | 22.0 |
+-----+-----+------+------+-------++-----+-----+-------+------+------+
| | 1/64| 467 | 234 | 106 || | 1/32| 148 | 74.0 | 43.3 |
|3/32 | 1/32| 306 | 153 | 69.5 || 1/8 | 1/16| 104 | 51.8 | 32.0 |
| | 1/16| 200 | 100 | 45.5 || | 1/8 | 69.6 | 34.8 | 20.3 |
| | 3/32| 156 | 78 | 35.5 ++-----+-----+-------+------+------+
+-----+-----+------+------+-------++ | 1/64| 183 | 91.6 | 68.0 |
| | 1/64| 417 | 209 | 94.8 ||3/16 | 1/32| 135 | 67.5 | 39.4 |
| 1/8 | 1/32| 273 | 136 | 62.0 || | 1/16| 94 | 47.0 | 27.4 |
| | 1/16| 179 | 89.3| 40.6 || | 1/8 | 64.3 | 32.2 | 18.8 |
| | 3/32| 140 | 69.8| 31.7 ++-----+-----+-------+------+------+
+-----+-----+------+------+-------++ | 1/64| 171 | 85.7 | 50.1 |
| | 1/64| 362 | 181 | 82.2 || 1/4 | 1/32| 126 | 63.2 | 36.9 |
|3/16 | 1/32| 236 | 118 | 53.8 || | 1/16| 87.8 | 43.9 | 25.6 |
| | 1/16| 155 | 77.4| 35.2 || | 3/32| 70.4 | 35.2 | 20.6 |
+-----+-----+------+------+-------++-----+-----+-------+------+------+
| 1/4 | 1/64| 328 | 164 | 74.5 || 3/8 | 1/64| 156 | 77.8 | 45.4 |
| | 1/32| 215 | 107 | 48.8 || | 1/32| 116 | 57.8 | 33.8 |
+-----+-----+------+------+-------++ | 1/16| 79.7 | 39.9 | 23.3 |
| 3/8 | 1/64| 286 | 143 | 65.0 || | | | | |
+-----+-----+------+------+-------++-----+-----+-------+------+------+
[1] Cutting speeds for tools of a good grade of high-speed steel,
properly ground and heat-treated.--From MACHINERY'S HANDBOOK.
=Average Cutting Speeds for Turning.=--The cutting speed is governed
principally by the hardness of the metal to be turned; the kind of steel
of which the turning tool is made; the shape of the tool and its
heat-treatment; the feed and depth of cut; whether or not a cooling
lubricant is used on the tool; the power of the lathe and also its
construction; hence it is impossible to give any definite rule for
determining either the speed, feed, or depth of cut, because these must
be varied to suit existing conditions. A general idea of the speeds used
in ordinary machine shop practice may be obtained from the following
figures:
Ordinary machine steel is generally turned at a speed varying between 45
and 65 feet per minute. For ordinary gray cast iron, the speed usually
varies from 40 to 50 feet per minute; for annealed tool steel, from 25
to 35 feet per minute; for soft yellow brass, from 150 to 200 feet per
minute; for hard bronze, from 35 to 80 feet per minute, the speed
depending upon the composition of the alloy. While these speeds
correspond closely to general practice, they can be exceeded for many
machining operations.
The most economical speeds for a given feed and depth of cut, as
determined by the experiments conducted by Mr. F. W. Taylor, are given
in the table, "Cutting Speeds and Feeds for Turning Tools." The speeds
given in this table represent results obtained with tools made of a good
grade of high-speed steel properly heat-treated and correctly ground. It
will be noted that the cutting speed is much slower for cast iron than
for steel. Cast iron is cut with less pressure or resistance than soft
steel, but the slower speed required for cast iron is probably due to
the fact that the pressure of the chip is concentrated closer to the
cutting edge, combined with the fact that cast iron wears the tool
faster than steel. The speeds given are higher than those ordinarily
used, and, in many cases, a slower rate would be necessary to prevent
chattering or because of some other limiting condition.
=Factors which limit the Cutting Speed.=--It is the durability of the
turning tool or the length of time that it will turn effectively
without grinding, that limits the cutting speed; and the hardness of the
metal being turned combined with the quality of the tool are the two
factors which largely govern the time that a tool can be used before
grinding is necessary. The cutting speed for very soft steel or cast
iron can be three or four times faster than the speed for hard steel or
hard castings, but whether the material is hard or soft, the kind and
quality of the tool used must also be considered, as the speed for a
tool made of ordinary carbon steel will have to be much slower than for
a tool made of modern "high-speed" steel.
When the cutting speed is too high, even though high-speed steel is
used, the point of the tool is softened to such an extent by the heat
resulting from the pressure and friction of the chip, that the cutting
edge is ruined in too short a time. On the other hand, when the speed is
too slow, the heat generated is so slight as to have little effect and
the tool point is dulled by being slowly worn or ground away by the
action of the chip. While a tool operating at such a low speed can be
used a comparatively long time without re-sharpening, this advantage is
more than offset by the fact that too much time is required for removing
a given amount of metal when the work is revolving so slowly.
Generally speaking, the speed should be such that a fair amount of work
can be done before the tool requires re-grinding. Evidently, it would
not pay to grind a tool every few minutes in order to maintain a high
cutting speed; neither would it be economical to use a very slow speed
and waste considerable time in turning, just to save the few minutes
required for grinding. For example, if a number of roughing cuts had to
be taken over a heavy rod or shaft, time might be saved by running at
such a speed that the tool would have to be sharpened (or be replaced by
a tool previously sharpened) when it had traversed half-way across the
work; that is, the time required for sharpening or changing the tool
would be short as compared with the gain effected by the higher work
speed. On the other hand, it might be more economical to run a little
slower and take a continuous cut across the work with one tool.
The experiments of Mr. Taylor led to the conclusion that, as a rule, it
is not economical to use roughing tools at a speed so slow as to cause
them to last more than 1-1/2 hour without being re-ground; hence the
speeds given in the table previously referred to are based upon this
length of time between grindings. Sometimes the work speed cannot be as
high as the tool will permit, because of the chattering that often
results when the lathe is old and not massive enough to absorb the
vibrations, or when there is unnecessary play in the working parts. The
shape of the tool used also affects the work speed, and as there are so
many things to be considered, the proper cutting speed is best
determined by experiment.
=Rules for Calculating Cutting Speeds.=--The number of revolutions
required to give any desired cutting speed can be found by multiplying
the cutting speed, in feet per minute, by 12 and dividing the product by
the circumference of the work in inches. Expressing this as a formula we
have
_C_ × 12
_R_ = --------
[pi]_d_
in which
_R_ = revolutions per minute;
_C_ = the cutting speed in feet per minute;
[pi] = 3.1416;
_d_ = the diameter in inches.
For example if a cutting speed of 60 feet per minute is wanted and the
diameter of the work is 5 inches, the required speed would be found as
follows:
60 × 12
_R_ = ---------- = 46 revolutions per minute.
3.1416 × 5
If the diameter is simply multiplied by 3 and the fractional part is
omitted, the calculation can easily be made, and the result will be
close enough for practical purposes. In case the cutting speed, for a
given number of revolutions and diameter, is wanted, the following
formula can be used:
_R_[pi]_d_
_C_ = ----------
12
Machinists who operate lathes do not know, ordinarily, what cutting
speeds, in feet per minute, are used for different classes of work, but
are guided entirely by past experience.
=Feed of Tool and Depth of Cut.=--The amount of feed and depth of cut
also vary like the cutting speed, for different conditions. When turning
soft machine steel the feed under ordinary conditions would vary between
1/32 and 1/16 inch per revolution. For turning soft cast iron the feed
might be increased to from 1/16 to 1/8 inch per revolution. These feeds
apply to fairly deep roughing cuts. Coarser feeds might be used in many
cases especially when turning large rigid parts in a powerful lathe. The
depth of a roughing cut in machine steel might vary from 1/8 to 3/8
inch, and in cast iron from 3/16 to 1/2 inch. These figures are intended
simply to give the reader a general idea of feeds and cuts that are
feasible under average conditions.
Ordinarily coarser feeds and a greater depth of cut can be used for cast
iron than for soft steel, because cast iron offers less resistance to
turning, but in any case, with a given depth of cut, metal can be
removed more quickly by using a coarse feed and the necessary slower
speed, than by using a fine feed and the higher speed which is possible
when the feed is reduced. When the turning operation is simply to remove
metal, the feed should be coarse, and the cut as deep as practicable.
Sometimes the cut must be comparatively light, either because the work
is too fragile and springy to withstand the strain of a heavy cut, or
the lathe has not sufficient pulling power. The difficulty with light
slender work is that a heavy cut may cause the part being turned to bend
under the strain, thus causing the tool to gouge in, which would
probably result in spoiling the work. Steadyrests can often be used to
prevent flexible parts from springing, as previously explained, but
there are many kinds of light work to which the steadyrest cannot be
applied to advantage.
The amount of feed to use for a finishing cut might, properly, be either
fine or coarse. Ordinarily, fine feeds are used for finishing steel,
especially if the work is at all flexible, whereas finishing cuts in
cast iron are often accompanied by a coarse feed. Fig. 15 illustrates
the feeds that are often used when turning cast iron. The view to the
left shows a deep roughing cut and the one to the right, a finishing
cut. By using a broad flat cutting edge set parallel to the tool's
travel, and a coarse feed for finishing, a smooth cut can be taken in a
comparatively short time. Castings which are close to the finished size
in the rough can often be finished to advantage by taking a single cut
with a broad tool, provided the work is sufficiently rigid. It is not
always practicable to use these broad tools and coarse feeds, as they
sometimes cause chattering, and when used on steel, a broad tool tends
to gouge or "dig in" unless the part being turned is rigid. Heavy steel
parts, however, are sometimes finished in this way. The modern method of
finishing many steel parts is to simply rough them out in a lathe to
within, say, 1/32 inch of the required diameter and take the finishing
cut in a cylindrical grinding machine.
[Illustration: Fig. 15. Roughing Cut--Light Finishing Cut and Coarse
Feed]
=Effect of Lubricant on Cutting Speed.=--When turning iron or steel a
higher cutting speed can be used, if a stream of soda water or other
cooling lubricant falls upon the chip at the point where it is being
removed by the tool. In fact, experiments have shown that the cutting
speed, when using a large stream of cooling water and a high-speed steel
tool, can be about 40 percent higher than when turning dry or without a
cooling lubricant. For ordinary carbon steel tools, the gain was about
25 per cent. The most satisfactory results were obtained from a stream
falling at a rather slow velocity but in large volume. The gain in
cutting speed, by the use of soda water or other suitable fluids, was
found to be practically the same for all qualities of steel from the
softest to the hardest.
Cast iron is usually turned dry or without a cutting lubricant.
Experiments, however, made to determine the effect of applying a heavy
stream of cooling water to a tool turning cast iron, showed the
following results: Cutting speed without water, 47 feet per minute;
cutting speed with a heavy stream of water, nearly 54 feet per minute;
increase in speed, 15 per cent. The dirt caused by mixing the fine
cast-iron turnings with a cutting lubricant is an objectionable feature
which, in the opinion of many, more than offsets the increase in cutting
speed that might be obtained.
Turret lathes and automatic turning machines are equipped with a pump
and piping for supplying cooling lubricant to the tools in a continuous
stream. Engine lathes used for general work, however, are rarely
provided with such equipment and a lubricant, when used, is often
supplied by a can mounted at the rear of the carriage, having a spout
which extends above the tool. Owing to the inconvenience in using a
lubricant on an engine lathe, steel, as well as cast iron, is often
turned dry especially when the work is small and the cuts light and
comparatively short.
=Lubricants Used for Turning.=--A good grade of lard oil is an excellent
lubricant for use when turning steel or wrought iron and it is
extensively used on automatic screw machines, especially those which
operate on comparatively small work. For some classes of work,
especially when high-cutting speeds are used, lard oil is not as
satisfactory as soda water or some of the commercial lubricants, because
the oil is more sluggish and does not penetrate to the cutting point
with sufficient rapidity. Many lubricants which are cheaper than oil are
extensively used on "automatics" for general machining operations. These
usually consist of a mixture of sal-soda (carbonate of soda) and water,
to which is added some ingredient such as lard oil or soft soap to
thicken or give body to the lubricant.
A cheap lubricant for turning, milling, etc., and one that has been
extensively used, is made in the following proportions: 1 pound of
sal-soda, 1 quart of lard oil, 1 quart of soft soap, and enough water to
make 10 or 12 gallons. This mixture is boiled for one-half hour,
preferably by passing a steam coil through it. If the solution should
have an objectionable odor, this can be eliminated by adding 2 pounds of
unslaked lime. The soap and soda in this solution improve the
lubricating quality and also prevent the surfaces from rusting. For
turning and threading operations, plain milling, deep-hole drilling,
etc., a mixture of equal parts of lard oil and paraffin oil will be
found very satisfactory, the paraffin being added to lessen the expense.
Brass or bronze is usually machined dry, although lard oil is sometimes
used for automatic screw machine work. Babbitt metal is also worked dry,
ordinarily, although kerosene or turpentine is sometimes used when
boring or reaming. If babbitt is bored dry, balls of metal tend to form
on the tool point and score the work. Milk is generally considered the
best lubricant for machining copper. A mixture of lard oil and
turpentine is also used for copper. For aluminum, the following
lubricants can be used: Kerosene, a mixture of kerosene and gasoline,
soap-water, or "aqualine" one part, water 20 parts.
=Lard Oil as a Cutting Lubricant.=--After being used for a considerable
time, lard oil seems to lose some of its good qualities as a cooling
compound. There are several reasons for this: Some manufacturers use the
same oil over and over again on different materials, such as brass,
steel, etc. This is objectionable, for when lard oil has been used on
brass it is practically impossible to get the fine dust separated from
it in a centrifugal separator. When this impure oil is used on steel,
especially where high-speed steels are employed, it does not give
satisfactory results, owing to the fact that when the cutting tool
becomes dull, the small brass particles "freeze" to the cutting tool and
thus produce rough work. The best results are obtained from lard oil by
keeping it thin, and by using it on the same materials--that is, not
transferring the oil from a machine in which brass is being cut to one
where it would be employed on steel. If the oil is always used on the
same class of material, it will not lose any of its good qualities.
Prime lard oil is nearly colorless, having a pale yellow or greenish
tinge. The solidifying point and other characteristics of the oil depend
upon the temperature at which it was expressed, winter-pressed lard oil
containing less solid constituents of the lard than that expressed in
warm weather. The specific gravity should not exceed 0.916; it is
sometimes increased by adulterants, such as cotton-seed and maize oils.
CHAPTER III
TAPER TURNING--SPECIAL OPERATIONS--FITTING
It is often necessary, in connection with lathe work, to turn parts
tapering instead of straight or cylindrical. If the work is mounted
between the centers, one method of turning a taper is to set the
tailstock center out of alignment with the headstock center. When both
of these centers are in line, the movement of the tool is parallel to
the axis of the work and, consequently, a cylindrical surface is
produced; but if the tailstock _h_{1}_ is set out of alignment, as shown
in Fig. 1, the work will then be turned tapering as the tool is
traversed from _a_ to _b_, because the axis _x--x_ is at an angle with
the movement of the tool. Furthermore the amount of taper or the
difference between the diameters at the ends for a given length, will
depend on how much center _h_{1}_ is set over from the central position.
[Illustration: Fig. 1. Taper Turning by the Offset-center Method]
[Illustration: Fig. 2. Examples of Taper Work]
The amount of taper is usually given on drawings in inches per foot, or
the difference in the diameter at points twelve inches apart. For
example, the taper of the piece shown at _A_, Fig. 2, is 1 inch per
foot, as the length of the tapering surface is just twelve inches and
the difference between the diameters at the ends is 1 inch. The conical
roller shown at _B_ has a total length of 9 inches and a tapering
surface 6 inches long, and in this case the taper per foot is also 1
inch, there being a difference of 1/2 inch in a length of 6 inches or 1
inch in twice that length. When the taper per foot is known, the amount
that the tailstock center should be set over for turning that taper can
easily be estimated, but it should be remembered that the setting
obtained in this way is not absolutely correct, and is only intended to
locate the center approximately. When a taper needs to be at all
accurate, it is tested with a gage, or by other means, after taking a
trial cut, as will be explained later, and the tailstock center is
readjusted accordingly. There are also more accurate methods of setting
the center, than by figuring the amount of offset, but as the latter is
often convenient this will be referred to first.
=Setting Tailstock Center for Taper Turning.=--Suppose the tailstock
center is to be set for turning part _C_, Fig. 2, to a taper of
approximately 1 inch per foot. In this case the center would simply be
moved toward the front of the machine 1/2 inch, or one-half the required
taper per foot, because the total length of the work happens to be just
12 inches. This setting, however, would not be correct for all work
requiring a taper of 1 inch per foot, as the adjustment depends not only
on the _amount_ of the taper but on the _total length_ of the piece.
[Illustration: Fig. 3. Detail View of Lathe Tailstock]
For example, the taper roller _B_ has a taper of 1 inch per foot, but
the center, in this case, would be offset less than one-half the taper
per foot, because the total length is only 9 inches. For lengths longer
or shorter than twelve inches, the taper per inch should be found first;
this is then multiplied by the _total_ length of the work (not the
length of the taper) which gives the taper for that length, and one-half
this taper is the amount to set over the center. For example, the taper
per inch of part _B_ equals 1 inch divided by 12 = 1/12 inch. The total
length of 9 inches multiplied by 1/12 inch = 3/4 inch, and 1/2 of 3/4 =
3/8, which is the distance that the tailstock center should be offset.
In this example if the taper per foot were not known, and only the
diameters of the large and small ends of the tapered part were given,
the difference between these diameters should first be found (2-1/2-2 =
1/2); this difference should then be divided by the length of the taper
(1/2 ÷ 6 = 1/12 inch) to obtain the taper per inch. The taper per inch
times the _total_ length represents what the taper would be if it
extended throughout the entire length, and one-half of this equals the
offset, which is 3/8 inch.
=Example of Taper Turning.=--As a practical example of taper turning let
us assume that the piece A, Fig. 4, which has been centered and
rough-turned as shown, is to be made into a taper plug, as indicated at
_B_, to fit a ring gage as at _C_. If the required taper is 1-1/2 inch
per foot and the total length is 8 inches, the tailstock center would be
offset 1/2 inch.
[Illustration: Fig. 4. Taper Plug and Gage]
To adjust the tailstock, the nuts _N_ (Fig. 3) are first loosened and
then the upper part _A_ is shifted sidewise by turning screw _S_. Scales
are provided on some tailstocks for measuring the amount of this
adjustment; if there is no scale, draw a line across the movable and
stationary parts _A_ and _B_, when the tailstock is set for straight
turning. The movement of the upper line in relation to the lower will
then show the offset, which can be measured with a scale.
When the adjustment has been made, nuts _N_ are tightened and the part
to be turned, with a dog attached, is placed between the centers the
same as for straight turning. The taper end is then reduced by turning,
but before it is near the finished size, the work is removed and the
taper tested by inserting it in the gage. If it is much out, this can be
felt, as the end that is too small can be shaken in the hole. Suppose
the plug did not taper enough and only the small end came into contact
with the gage, as shown somewhat exaggerated at _D_; in that case the
center would be shifted a little more towards the front, whereas if the
taper were too steep, the adjustment would, of course, be in the
opposite direction. A light cut would then be taken, to be followed by
another test. If the plug should fit the gage so well that there was no
perceptible shake, it could be tested more closely as follows: Draw
three or four chalk lines along the tapering surface, place the work in
the gage and turn it a few times. The chalk marks will then show whether
the taper of the plug corresponds to that of the gage; for example, if
the taper is too great, the marks will be rubbed out on the large end,
but if the taper is correct, the lines throughout their length will be
partially erased.
[Illustration: Fig. 5. Setting Work for Taper Turning by use of Caliper
Gage]
Another and more accurate method of testing tapers is to apply a thin
coat of Prussian-blue to one-half of the tapering surface, in a
lengthwise direction. The work is then inserted in the hole or gage and
turned to mark the bearing. If the taper is correct, the bearing marks
will be evenly distributed, whereas if the taper is incorrect, they will
appear at one end. Tapering pieces that have to be driven tightly into a
hole, such as a piston-rod, can be tested by the location of the bearing
marks produced by actual contact.
After the taper is found to be correct, the plug is reduced in size
until it just enters the gage as at _C_. The final cut should leave it
slightly above the required size, so that a smooth surface can be
obtained by filing. It should be mentioned that on work of this kind,
especially if great accuracy is required, the final finish is often
obtained by grinding in a regular grinding machine, instead of by
filing. When this method is employed, a lathe is used merely to
rough-turn the part close to size.
[Illustration: Fig. 6. Side View showing Relative Positions of Gage and
Work]
When the amount that the tailstock center should be offset is determined
by calculating, as in the foregoing example, it is usually necessary to
make slight changes afterward, and the work should be tested before it
is too near the finished size so that in case one or more trial cuts are
necessary, there will be material enough to permit this. When there are
a number of tapered pieces to be turned to the same taper, the
adjustment of the tailstock center will have to be changed unless the
total length of each piece and the depth of the center holes are the
same in each case.
=Setting the Tailstock Center with a Caliper Tool.=--Another method of
setting the tailstock center for taper turning is illustrated in Fig. 5.
The end of an engine piston-rod is to be made tapering as at A and to
dimensions _a_, _b_, _c_ and _d_. It is first turned with the centers in
line as at _B_. The end _d_ is reduced to diameter _b_ up to the
beginning of the taper and it is then turned to diameter _a_ as far as
the taper part _c_ extends. The tailstock center is next set over by
guess and a caliper tool is clamped in the toolpost. This tool, a side
view of which is shown in Fig. 6, has a pointer _p_ that is free to
swing about pivot _r_, which should be set to about the same height as
the center of the work. The tailstock center is adjusted until this
pointer just touches the work when in the positions shown by the full
and dotted lines at _C_, Fig. 5; that is, until the pointer makes
contact at the beginning and end of the taper part. The travel of the
carriage will then be parallel to a line _x--x_, representing the taper;
consequently, if a tool is started at the small end, as shown by the
dotted lines at _D_, with the nose just grazing the work, it will also
just graze it when fed to the extreme left as shown. Of course, if the
taper were at all steep, more than one cut would be taken.
[Illustration: Fig. 7. Obtaining Tailstock Center Adjustment by use of
Square]
If these various operations are carefully performed, a fairly accurate
taper can be produced. The straight end _d_ is reduced to size after the
tail-center is set back to the central position. Some mechanics turn
notches or grooves at the beginning and end of the tapering part, having
diameters equal to the largest and smallest part of the taper; the work
is then set by these grooves with a caliper tool. The advantage of the
first method is that most of the metal is removed while the centers are
in alignment.
[Illustration: Fig. 8. Second Step in Adjusting Tailstock Center by use
of Square]
=Setting the Tailstock Center with a Square.=--Still another method of
adjusting the tailstock for taper turning, which is very simple and
eliminates all figuring, is as follows: The part to be made tapering is
first turned cylindrical or straight for 3 or 4 inches of its length,
after the ends have been properly centered and faced square. The work is
then removed and the tailstock is shifted along the bed until the
distance _a--b_ between the extreme points of the centers is exactly 1
foot. The center is next offset a distance _b--c_ equal to one-half the
required taper per foot, after which a parallel strip _D_, having true
sides, is clamped in the toolpost. Part _D_ is then set at right angles
to a line passing from one center point to the other. This can be done
conveniently by holding a 1-foot square (preferably with a sliding head)
against one side of _D_ and adjusting the latter in the toolpost until
edge _E_ of the square blade is exactly in line with both center points.
After part _D_ is set, it should be clamped carefully to prevent
changing the position. The angle between the side of _D_ and an
imaginary line which is perpendicular to axis _a--b_ is now equal to
one-half the angle of the required taper.
The axis of the part to be turned should be set parallel with line _E_,
which can be done by setting the cylindrical surface which was
previously finished, at right angles to the side of _D_. In order to do
this the work is first placed between centers, the tailstock being
shifted along the bed if necessary; the tail-center is then adjusted
laterally until the finished cylindrical surface is square with the side
of _D_. A small try-square can be used for testing the position of the
work, as indicated in Fig. 8. If the length of the work is less than 1
foot, it will be necessary to move the center toward the rear of the
machine, and if the length is greater than 1 foot, the adjustment is, of
course, in the opposite direction.
[Illustration: Fig. 9. A Lathe Taper Attachment]
=The Taper Attachment.=--Turning tapers by setting over the tailstock
center has some objectionable features. When the lathe centers are not
in alignment, as when set for taper turning, they bear unevenly in the
work centers because the axis of the work is at an angle with them; this
causes the work centers to wear unevenly and results in inaccuracy.
Furthermore, the adjustment of the tailstock center must be changed when
turning duplicate tapers, unless the length of each piece and the depth
of the center holes are the same. To overcome these objections, many
modern lathes are equipped with a special device for turning tapers,
known as a taper attachment, which permits the lathe centers to be kept
in alignment, as for cylindrical turning, and enables more accurate work
to be done.
[Illustration: Fig. 10. Sectional View of Taper Attachment]
Taper attachments, like lathes, vary some in their construction, but all
operate on the same principle. An improved form of taper attachment is
illustrated in Figs. 9 and 10. Fig. 9 shows a plan view of a lathe
carriage with an attachment fitted to it, and Fig. 10 a sectional view.
This attachment has an arm _A_ on which is mounted a slide _S_ that can
be turned about a central pivot by adjusting screw _D_. The arm _A_ is
supported by, and is free to slide on, a bracket _B_ (see also sectional
view) that is fastened to the carriage, and on one end of the arm there
is a clamp _C_ that is attached to the lathe bed when turning tapers. On
the slide _S_ there is a shoe _F_ that is connected to bar _E_ which
passes beneath the toolslide. The rear end of the cross-feed screw is
connected to this bar, and the latter is clamped to the toolslide when
the attachment is in use.
When a taper is to be turned, the carriage is moved opposite the taper
part and clamp _C_ is fastened to the bed; this holds arm _A_ and slide
_S_ stationary so that the carriage, with bracket _B_ and shoe _F_, can
be moved with relation to the slide. If this slide _S_ is set at an
angle, as shown, the shoe as it moves along causes the toolslide and
tool to move in or out, but if the slide is set parallel to the carriage
travel, the toolslide remains stationary. Now if the tool, as it feeds
lengthwise of the work, is also gradually moved crosswise, it will turn
a taper, and as this crosswise movement is caused by the angularity of
slide _S_, different tapers are obtained by setting the slide to
different positions.
By means of a graduated scale _G_ at the end of slide _S_, the taper
that will be obtained for any angular position of the slide is shown. On
some attachments there are two sets of graduations, one giving the taper
in inches per foot and the other in degrees. While tapers are ordinarily
given in inches per foot on drawings, sometimes the taper is given in
degrees instead. The attachment is set for turning tapers by adjusting
slide _S_ until pointer _p_ is opposite the division or fractional part
of a division representing the taper. The whole divisions on the scale
represent taper in inches per foot, and by means of the sub-divisions,
the slide can be set for turning fractional parts of an inch per foot.
When slide _S_ is properly set, it is clamped to arm _A_ by the nuts
_N_. Bar _E_ is also clamped to the toolslide by bolt _H_, as previously
stated. The attachment is disconnected for straight turning by simply
loosening clamp _C_ and the bolt _H_.
=Application of Taper Attachment.=--Practical examples of lathe work,
which illustrate the use of the taper attachment, are shown in Figs, 11
and 12. Fig. 11 shows how a taper hole is bored in an engine
piston-head, preparatory to reaming. The casting must be held either in
a chuck _C_ or on a faceplate if too large for the chuck. The side of
the casting (after it has been "chucked") should run true, and also the
circumference, unless the cored hole for the rod is considerably out of
center, in which case the work should be shifted to divide the error.
The side of the casting for a short space around the hole is faced true
with a round nose turning tool, after which the rough-cored hole is
bored with an ordinary boring tool _t_, and then it is finished with a
reamer to exactly the right size and taper.
This particular taper attachment is set to whatever taper is given on
the drawing, by loosening nuts _N_ and turning slide _S_ until pointer
_P_ is opposite that division on the scale which represents the taper.
The attachment is then ready, after bolt _H_ and nuts _N_ are tightened,
and clamp _C_ is fastened to the lathe bed. The hole is bored just as
though it were straight, and as the carriage advances, the tool is
gradually moved inward by the attachment. If the lathe did not have a
taper attachment, the taper hole could be bored by using the compound
rest.
[Illustration: Fig. 11. Lathe with Taper Attachment arranged for Boring
Taper Hole in Engine Piston]
The hole should be bored slightly less than the finish size to allow for
reaming. When a reamer is used in the lathe, the outer end is supported
by the tailstock center and should have a deep center-hole. The lathe is
run very slowly for reaming and the reamer is fed into the work by
feeding out the tailstock spindle. The reamer can be kept from
revolving, either by attaching a heavy dog to the end or, if the end is
squared, by the use of a wrench long enough to rest against the lathe
carriage. A common method is to clamp a dog to the reamer shank, and
then place the tool-rest beneath it to prevent rotation. If the shank
of a tool is clamped to the toolpost so that the dog rests against it,
the reamer will be prevented from slipping off the center as it tends to
do; with this arrangement, the carriage is gradually moved along as the
tailstock spindle is fed outward. Some reamers are provided with
stop-collars which come against the finished side of the casting when
the hole has been reamed to size.
After the reaming operation, the casting is removed from the chuck and a
taper mandrel is driven into the hole for turning the outside of the
piston. This mandrel should run true on its centers, as otherwise the
outside surface of the piston will not be true with the bored hole. The
driving dog, especially for large work of this kind, should be heavy and
stiff, because light flexible clamps or dogs vibrate and frequently
cause chattering. For such heavy work it is also preferable to drive at
two points on opposite sides of the faceplate, but the driving pins
should be carefully adjusted to secure a uniform bearing on both sides.
The foregoing method of machining a piston is one that would ordinarily
be followed when using a standard engine lathe, and it would, perhaps,
be as economical as any if only one piston were being made; but where
such work is done in large quantities, time could be saved by proceeding
in a different way. For example, the boring and reaming operation could
be performed much faster in a turret lathe, which is a type designed for
just such work, but a turret lathe cannot be used for as great a variety
of turning operations as a lathe of the regular type. There are also
many other classes of work that can be turned more quickly in special
types of machines, but as more or less time is required for arranging
these special machines and often special tools have to be made, the
ordinary lathe is frequently indispensable when only a few parts are
needed; in addition, it is better adapted to some turning operations
than any other machine.
Fig. 12 illustrates how a taper attachment would be used for turning the
taper fitting for the crosshead end of an engine piston-rod. Even though
this taper corresponds to the taper of the hole in the piston, slide _S_
would have to be reset to the corresponding division on the opposite
side of the central zero mark, because the taper of the hole decreased
in size during the boring operation, whereas the rod is smallest at the
beginning of the cut, so that the tool must move outward rather than
inward as it advances. The taper part is turned practically the same as
a cylindrical part; that is, the power feed is used and, as the carriage
moves along the bed, the tool is gradually moved outward by the taper
attachment.
[Illustration: Fig. 12. Taper Attachment Set for Turning Taper End of
Piston-rod]
If the rod is being fitted directly to the crosshead (as is usually the
case), the approximate size of the small end of the taper could be
determined by calipering, the calipers being set to the size of the hole
at a distance from the shoulder or face side of the crosshead, equal to
the length of the taper fitting on the rod. If the crosshead were bored
originally to fit a standard plug gage, the taper on the rod could be
turned with reference to this gage, but, whatever the method, the taper
should be tested before turning too close to the finished size. The test
is made by removing the rod from the lathe and driving it tightly into
the crosshead. This shows how near the taper is to size, and when the
rod is driven out, the bearing marks show whether the taper is exactly
right or not. If the rod could be driven in until the shoulder is, say,
1/8 inch from the crosshead face, it would then be near enough to finish
to size by filing. When filing, the lathe is run much faster than for
turning, and most of the filing should be done where the bearing marks
are the heaviest, to distribute the bearing throughout the length of the
taper. Care should be taken when driving the rod in or out, to protect
the center-holes in the ends by using a "soft" hammer or holding a piece
of soft metal against the driving end.
[Illustration: Fig. 13. Tool Point should be in same Horizontal Plane as
Axis of Work for Taper Turning]
After the crosshead end is finished, the rod is reversed in the lathe
for turning the piston end. The dog is clamped to the finished end,
preferably over a piece of sheet copper to prevent the surface from
being marred. When turning this end, either the piston reamer or the
finished hole in the piston can be calipered. The size and angle of the
taper are tested by driving the rod into the piston, and the end should
be fitted so that by driving tightly, the shoulder will just come up
against the finished face of the piston. When the taper is finished, the
attachment is disengaged and a finishing cut is taken over the body of
the rod, unless it is to be finished by grinding, which is the modern
and most economical method.
=Height of Tool when Turning Tapers.=--The cutting edge of the tool,
when turning tapers, should be at the same height as the center or axis
of the work, whether an attachment is used or not. The importance of
this will be apparent by referring to Fig. 13. To turn the taper shown,
the tool _T_ would be moved back a distance _x_ (assuming that an
attachment is used) while traversing the length _l_. As an illustration,
if the tool could be placed as high as point _a_, the setting of the
attachment remaining as before, the tool would again move back a
distance _x_, while traversing a distance _l_, but the large end would
be under-sized (as shown by the dotted line) if the diameters of the
small ends were the same in each case. Of course, if the tool point were
only slightly above or below the center, the resulting error would also
be small. The tool can easily be set central by comparing the height of
the cutting edge at the point of the tool with one of the lathe centers
before placing the work in the lathe.
[Illustration: Fig. 14. Plan View showing Method of Turning a Taper with
the Compound Rest]
=Taper Turning with the Compound Rest.=--The amount of taper that can be
turned by setting over the tailstock center and by the taper attachment
is limited, as the centers can only be offset a certain distance, and
the slide _S_ (Fig. 9) of the attachment cannot be swiveled beyond a
certain position. For steep tapers, the compound rest _E_ is swiveled to
the required angle and used as indicated in Fig. 14, which shows a plan
view of a rest set for turning the valve _V_. This compound rest is an
upper slide mounted on the lower or main cross-slide _D_, and it can be
turned to any angular position so that the tool, which ordinarily is
moved either lengthwise or crosswise of the bed, can be fed at an angle.
The base of the compound rest is graduated in degrees and the position
of these graduations shows to what angle the upper slide is set. Suppose
the seat of valve _V_ is to be turned to an angle of 45 degrees with the
axis or center, as shown on the drawing at _A_, Fig. 15. To set the
compound rest, nuts _n_ on either side, which hold it rigidly to the
lower slide, are first loosened and the slide is then turned until the
45-degree graduation is exactly opposite the zero line; the slide is
then tightened in this position. A cut is next taken across the valve by
operating handle _w_ and feeding the tool in the direction of the arrow.
[Illustration: Fig. 15. Example of Taper Work Turned by using Compound
Rest]
In this particular instance the compound rest is set to the same angle
given on the drawing, but this is not always the case. If the draftsman
had given the included angle of 90 degrees, as shown at _B_, which would
be another way of expressing it, the setting of the compound rest would,
of course, be the same as before, or to 45 degrees, but the number of
degrees marked on the drawing does not correspond with the angle to
which the rest must be set. As another illustration, suppose the valve
were to be turned to an angle of 30 degrees with the axis as shown at
_C_. In this case the compound rest would not be set to 30 degrees but
to 60 degrees, because in order to turn the work to an angle of 30
degrees, the rest must be 60 degrees from its zero position, as shown.
From this it will be seen that the number of degrees marked on the
drawing does not necessarily correspond to the angle to which the rest
must be set, as the graduations on the rest show the number of degrees
that it is moved from its zero position, which corresponds to the line
_a--b_. The angle to which the compound rest should be set can be found,
when the drawing is marked as at _A_ or _C_, by subtracting the angle
given from 90 degrees. When the included angle is given, as at _B_,
subtract one-half the included angle from 90 degrees to obtain the
required setting. Of course, when using a compound rest, the lathe
centers are set in line as for straight turning, as otherwise the angle
will be incorrect.
Rules for Figuring Tapers
+---------------------+---------------------+--------------------------+
| Given | To Find | Rule |
+---------------------+---------------------+--------------------------+
|The taper per foot. |The taper per inch. |Divide the taper per foot |
| | | by 12. |
| | | |
|The taper per inch. |The taper per foot. |Multiply the taper per |
| | | inch by 12. |
| | | |
|End diameters and |The taper per foot. |Subtract small diameter |
| length of taper in | | from large; divide by |
| inches. | | length of taper, and |
| | | multiply quotient by 12.|
| | | |
|Large diameter and |Diameter at small |Divide taper per foot by |
| length of taper in | end in inches. | 12; multiply by length |
| inches and taper | | of length of taper, and |
| per foot. | | subtract result from |
| | | large diameter. |
| | | |
|Small diameter and |Diameter at large |Divide taper per foot by |
| length of taper in | end in inches. | 12; multiply by length |
| inches, and taper | | of taper, and add result|
| per foot. | | to small diameter. |
| | | |
|The taper per foot |Distance between | Subtract small diameter |
| and two diameters | two given diameters| from large; divide re- |
| in inches. | in inches. | mainder by taper per |
| | | foot, and multiply |
| | | quotient by 12. |
| | | |
|The taper per foot. |Amount of taper in | Divide taper per foot by |
| | a certain length | 12; multiply by given |
| | given in inches. | length of tapered part.|
+---------------------+---------------------+--------------------------+
=Accurate Measurement of Angles and Tapers.=--When great accuracy is
required in the measurement of angles, or when originating tapers,
disks are commonly used. The principle of the disk method of taper
measurement is that if two disks of unequal diameters are placed either
in contact or a certain distance apart, lines tangent to their
peripheries will represent an angle or taper, the degree of which
depends upon the diameters of the two disks and the distance between
them. The gage shown in Fig. 16, which is a form commonly used for
originating tapers or measuring angles accurately, is set by means of
disks. This gage consists of two adjustable straight-edges _A_ and
_A_{1}_, which are in contact with disks _B_ and _B_{1}_. The angle
[alpha] or the taper between the straight-edges depends, of course, upon
the diameters of the disks and the center distance _C_, and as these
three dimensions can be measured accurately, it is possible to set the
gage to a given angle within very close limits. Moreover, if a record of
the three dimensions is kept, the exact setting of the gage can be
reproduced quickly at any time. The following rules may be used for
adjusting a gage of this type.
[Illustration: Fig. 16. Disk Gage for Accurate Measurement of Angles and
Tapers]
=To Find Center Distance for a Given Taper.=--When the taper, in inches
per foot, is given, to determine center distance _C_. _Rule:_ Divide the
taper by 24 and find the angle corresponding to the quotient in a table
of tangents; then find the sine corresponding to this angle and divide
the difference between the disk diameters by twice the sine.
_Example:_ Gage is to be set to 3/4 inch per foot, and disk diameters
are 1.25 and 1.5 inch, respectively. Find the required center distance
for the disks.
0.75
---- = 0.03125.
24
The angle whose tangent is 0.03125 equals 1 degree 47.4 minutes; sin 1°
47.4' = 0.03123; 1.50 - 1.25 = 0.25 inch;
0.25
----------- = 4.002 inches = center distance C.
2 × 0.03123
=To Find Center Distance for a Given Angle.=--When straight-edges must
be set to a given angle [alpha], to determine center distance _C_
between disks of known diameter. _Rule:_ Find the sine of half the angle
[alpha] in a table of sines; divide the difference between the disk
diameters by double this sine.
_Example:_ If an angle [alpha] of 20 degrees is required, and the disks
are 1 and 3 inches in diameter, respectively, find the required center
distance _C_.
20
---- = 10 degrees; sin 10° = 0.17365;
2
3 - 1
----------- = 5.759 inches = center distance _C_.
2 × 0.17365
=To Find Angle for Given Taper per Foot.=--When the taper in inches per
foot is known, and the corresponding angle [alpha] is required. _Rule:_
Divide the taper in inches per foot by 24; find the angle corresponding
to the quotient, in a table of tangents, and double this angle.
_Example:_ What angle [alpha] is equivalent to a taper of 1-1/2 inch per
foot?
1.5
--- = 0.0625.
24
The angle whose tangent is 0.0625 equals 3 degrees 35 minutes, nearly;
then, 3 deg. 35 min. × 2 = 7 deg. 10 min.
=To Find Angle for Given Disk Dimensions.=--When the diameters of the
large and small disks and the center distance are given, to determine
the angle [alpha]. _Rule:_ Divide the difference between the disk
diameters by twice the center distance; find the angle corresponding to
the quotient, in a table of sines, and double the angle.
_Example:_ If the disk diameters are 1 and 1.5 inch, respectively, and
the center distance is 5 inches, find the included angle [alpha].
1.5 - 1
------- = 0.05.
2 × 5
The angle whose sine is 0.05 equals 2 degrees 52 minutes; then, 2 deg.
52 min. × 2 = 5 deg. 44 min. = angle [alpha].
[Illustration: Fig. 17. Setting Center Mark in Line with Axis of Lathe
Spindle by use of Test Indicator]
[Illustration: Fig. 18. Jig-plate with Buttons attached, ready for
Boring]
=Use of the Center Indicator.--=The center test indicator is used for
setting a center-punch mark, the position of which corresponds with the
center or axis of the hole to be bored, in alignment with the axis of
the lathe spindle. To illustrate, if two holes are to be bored, say 5
inches apart, small punch marks having that center-to-center distance
would be laid out as accurately as possible. One of these marks would
then be set central with the lathe spindle by using a center test
indicator as shown in Fig. 17. This indicator has a pointer _A_ the end
of which is conical and enters the punch mark. The pointer is held by
shank _B_ which is fastened in the toolpost. The joint _C_ by means of
which the pointer is held to the shank is universal; that is, it allows
the pointer to move in any direction. Now when the part being tested is
rotated by running the lathe, if the center-punch mark is not in line
with the axes of the lathe spindle, obviously the outer end of pointer
_A_ will vibrate, and as joint _C_ is quite close to the inner end, a
very slight error in the location of the center-punch mark will cause a
perceptible movement of the outer end, as indicated by the dotted lines.
When the work has been adjusted until the pointer remains practically
stationary, the punch mark is central, and the hole is bored. The other
center-punch mark is then set in the same way for boring the second
hole. The accuracy of this method depends, of course, upon the location
of the center-punch marks. A still more accurate way of setting parts
for boring holes to a given center-to-center distance is described in
the following:
=Locating Work by the Button Method.=--Among the different methods
employed by machinists and toolmakers for accurately locating work such
as jigs, etc., on the faceplate of a lathe, the one most commonly used
is known as the button method. This scheme is so named because
cylindrical bushings or buttons are attached to the work in positions
corresponding to the holes to be bored, after which they are used in
locating the work. These buttons, which are ordinarily about 1/2 inch in
diameter, are ground and lapped to the same size and the ends squared.
The diameter should, preferably, be such that the radius can be
determined easily, and the hole through the center should be about 1/8
inch larger than the retaining screw, so that the button can be shifted.
As an illustration of the practical application of the button method, we
shall consider, briefly, the way the holes would be accurately machined
in the jig-plate in Fig. 18. First the centers of the seven holes should
be laid off approximately correct by the usual methods, after which
small holes should be drilled and tapped for the clamping screws _S_.
After the buttons _B_ are clamped lightly in place, they are all set in
correct relation with each other and with the jig-plate. The proper
location of the buttons is very important as their positions largely
determine the accuracy of the work. A definite method of procedure that
would be applicable in all cases cannot, of course, be given, as the
nature of the work as well as the tools available make it necessary to
employ different methods.
[Illustration: Fig. 19. Setting a Button True Preparatory to Boring, by
use of Test Indicator]
In this particular case, the three buttons _a_, _b_ and _c_ should be
set first, beginning with the one in the center. As this central hole
must be 2.30 and 2.65 inches from the finished sides _A_ and _A_{1}_,
respectively, the work is first placed on an accurate surface-plate as
shown; by resting it first on one of these sides and then on the other,
and measuring with a vernier height gage, the central button can be
accurately set. The buttons _a_ and _c_ are also set to the correct
height from side _A_{1}_ by using the height gage, and in proper
relation to the central button by using a micrometer or a vernier
caliper and measuring the over-all dimension _x_. When measuring in this
way, the diameter of one button would be deducted to obtain the correct
center-to-center distance. After buttons _a_, _b_ and _c_ are set
equidistant from side A_{1} and in proper relation to each other, the
remaining buttons should be set radially from the central button _b_ and
the right distance apart. By having two micrometers or gages, one set
for the radial dimension _x_ and the other for the chordal distance _y_,
the work may be done in a comparatively short time.
[Illustration: Fig. 20. Testing Concentricity of Button with Dial Gage]
After the buttons have been tightened, all measurements should be
carefully checked; the work is then mounted on the faceplate of the
lathe, and one of the buttons, say _b_, is set true by the use of a test
indicator as shown in Fig. 19. When the end of this indicator (which is
one of a number of types on the market) is brought into contact with the
revolving button, the vibration of the pointer _I_ shows how much the
button runs out of true. When the pointer remains practically
stationary, thus showing that the button runs true, the latter should be
removed. The hole is then drilled nearly to the required size, after
which it is bored to the finish diameter. In a similar manner the other
buttons are indicated and the holes bored, one at a time. It is evident
that if each button is correctly located and set perfectly true in the
lathe, the various holes will be located at the required
center-to-center dimensions within very close limits.
[Illustration: Fig. 21. Drilling a Bushing Hole]
Fig. 20 shows how one of the buttons attached to a plate in which three
holes are to be bored is set true or concentric. The particular
indicator illustrated is of the dial type, any error in the location of
the button being shown by a hand over a dial having graduations
representing thousandths of an inch. Fig. 21 shows how the hole is
drilled after the button is removed. It will be noted that the drill is
held in a chuck, the taper shank of which fits into the tailstock
spindle, this being the method of holding small drills. After drilling,
the hole is bored as shown in Fig. 22. The boring tool should have a
keen edge to avoid springing, and if the work when clamped in position,
throws the faceplate out of balance, it is advisable to restore the
balance, before boring, by the use of a counter-weight, because the
lathe can be rotated quite rapidly when boring such a small hole.
[Illustration: Fig. 22. Boring a Bushing Hole]
When doing precision work of this kind, the degree of accuracy will
depend upon the instruments used, the judgment and skill of the workman
and the care exercised. A good general rule to follow when locating
bushings or buttons is to use the method which is the most direct and
which requires the least number of measurements. As an illustration of
how errors may accumulate, let us assume that seven holes are to be
bored in the jig-plate shown in Fig. 23, so that they are the same
distance from each other and in a straight line. The buttons may be
brought into alignment by the use of a straight-edge, and to simplify
matters, it will be taken for granted that they have been ground and
lapped to the same size. If the diameter of the buttons is first
determined by measuring with a micrometer, and then this diameter is
deducted from the center distance _x_, the difference will be the
distance _y_ between adjacent buttons. Now if a temporary gage is made
to length _y_, all the buttons can be set practically the same distance
apart, the error between any two adjacent ones being very slight. If,
however, the total length _z_ over the end buttons is measured by some
accurate means, the chances are that this distance will not equal six
times dimension _x_ plus the diameter of one button, as it should,
because even a very slight error in the gage for distance _y_ would
gradually accumulate as each button was set. If a micrometer were
available that would span two of the buttons, the measurements could be
taken direct and greater accuracy would doubtless be obtained. On work
of this kind where there are a number of holes that need to have
accurate over-all dimensions, the long measurements should first be
taken when setting the buttons, providing, of course, there are proper
facilities for so doing, and then the short ones. For example, the end
buttons in this case should first be set, then the central one and
finally those for the sub-divisions.
[Illustration: Fig. 23. Example of Work illustrating Accumulation of
Errors]
=Eccentric Turning.=--When one cylindrical surface must be turned
eccentric to another, as when turning the eccentric of a steam engine,
an arbor having two sets of centers is commonly used, as shown in Fig.
24. The distance _x_ between the centers must equal one-half the total
"throw" or stroke of the eccentric. The hub of the eccentric is turned
upon the centers _a--a_, and the tongued eccentric surface, upon the
offset centers, as indicated by the illustration. Sometimes eccentrics
are turned while held upon special fixtures attached to the faceplate.
[Illustration: Fig. 24. Special Arbor for Turning Eccentrics]
When making an eccentric arbor, the offset center in each end should be
laid out upon radial lines which can be drawn across the arbor ends by
means of a surface gage. Each center is then drilled and reamed to the
same radius _x_ as near as possible. The uniformity of the distance _x_
at each end is then tested by placing the mandrel upon the offset
centers and rotating it, by hand, with a dial indicator in contact at
first one end and then the other. The amount of offset can also be
tested either by measuring from the point of a tool held in the
toolpost, or by setting the tool to just graze the mandrel at extreme
inner and outer positions, and noting the movement of the cross-slide by
referring to the dial gage of the cross-feed screw.
[Illustration: Fig. 25. Turning an Engine Crank-pin in an Ordinary
Lathe]
=Turning a Crankshaft in a Lathe.=--Another example of eccentric turning
is shown in Fig. 25. The operation is that of turning the crank-pin of
an engine crankshaft, in an ordinary lathe. The main shaft is first
rough-turned while the forging revolves upon its centers _C_ and _C_{1}_
and the ends are turned to fit closely the center-arms _A_ and _A_{1}_.
After the sides _B_ and _B_{1}_ of the crank webs have been rough-faced,
the center-arms are attached to the ends of the shaft as shown in the
illustration. These arms have centers at _D_ and _D_{1}_ (located at the
required crank radius) which should be aligned with the rough pin, when
attaching the arms, and it is advisable to insert braces _E_ between the
arms and crank to take the thrust of the lathe centers. With the forging
supported in this way, the crank-pin and inner sides of the webs are
turned and faced, the work revolving about the axis of the pin. The
turning tools must extend beyond the tool-holder far enough to allow the
crank to clear as it swings around. Owing to this overhang, the tool
should be as heavy as possible to make it rigid and it is necessary to
take comparatively light cuts and proceed rather cautiously. After
finishing the crank-pin and inside of the crank, the center-arms are
removed and the main body of the shaft and the sides _B_ and _B_{1}_ are
finished. This method of turning crankshafts is often used in general
repair shops, etc., especially where new shafts do not have to be turned
very often. It is slow and inefficient, however, and where crankshafts
are frequently turned, special machines or attachments are used.
[Illustration: Fig. 26. LeBlond Lathe with Special Equipment for
Crankshaft Turning]
=Special Crankshaft Lathe.=--A lathe having special equipment for
rough-turning gas engine crankshaft pins is shown in Fig. 26. This
lathe is a heavy-duty type built by the R. K. LeBlond Machine Tool Co.
It is equipped with special adjustable headstock and tailstock fixtures
designed to take crankshafts having strokes up to about 6 inches. The
tools are held in a three-tool turret type of toolpost and there are
individual cross-stops for each tool. This lathe also has a roller
steadyrest for supporting the crankshaft; automatic stops for the
longitudinal feed, and a pump for supplying cutting lubricant. The
headstock fixture is carried on a faceplate mounted on the spindle and
so arranged as to be adjustable for cranks of different throw. When the
proper adjustment for a given throw has been made, the slide is secured
by four T-bolts. A graduated scale and adjusting screw permit of
accurate adjustments.
The revolving fixture is accurately indexed for locating different
crank-pins in line with the lathe centers, by a hardened steel plunger
in the slide which engages with hardened bushings in the fixture. The
index is so divided that the fixture may be rotated 120 or 180 degrees,
making it adjustable for 2-, 4- and 6-throw cranks. After indexing, the
fixture is clamped by two T-bolts which engage a circular T-slot. The
revolving fixture is equipped with removable split bushings which can be
replaced to fit the line bearings of different sized crankshafts. The
work is driven by a V-shaped dovetail piece having a hand-nut
adjustment, which also centers the pin by the cheek or web. The crank is
held in position by a hinged clamp on the fixture. The tailstock fixture
is also adjustable and it is mounted on a spindle which revolves in a
bushing in the tailstock barrel. The adjustment is obtained in the same
manner as on the headstock fixture, and removable split bushings as well
as a hinged clamp are also employed.
The method of chucking a four-throw crank is as follows: The two
fixtures are brought into alignment by two locking pins. One of these is
located in the head and enters a bushing in the large faceplate and the
other is in the tailstock and engages the tailstock fixture. The
crankshaft is delivered to the machine with the line bearings
rough-turned and it is clamped by the hinged clamp previously referred
to and centered by the V-shaped driver. The locking pins for both
fixtures are then withdrawn and the machine is ready to turn two of the
pins. After these have been machined, the fixtures are again aligned by
the locking pins, the two T-bolts of the headstock fixture and the
hinged clamp at the tailstock are released, the indexing plunger is
withdrawn and the headstock fixture and crank are turned 180 degrees or
until the index plunger drops into place. The crank is then clamped at
the tailstock end and the revolving fixture is secured by the two
T-bolts previously referred to. After the locking pins are withdrawn,
the lathe is ready to turn the two opposite pins.
[Illustration: Fig. 27. Diagrams showing Arrangements of Tools on
LeBlond Lathe]
=Operation of Special Crankshaft Lathe.=--The total equipment of this
machine (see Fig. 27) is carried on a three-tool turret tool-block. The
method of turning a crankshaft is as follows: A round-nosed turning tool
is first fed into a cross stop as illustrated in the plan view at _A_,
which gives the proper diameter. The feed is then engaged and the tool
feeds across the pin until the automatic stop lever engages the first
stop, which throws out the feed automatically. The carriage is then
moved against a positive stop by means of the handwheel. The roller
back-rest is next adjusted against the work by the cross-feed handwheel
operating through a telescopic screw, and the filleting tools are
brought into position as at _B_. These are run in against a stop,
removing the part left by the turning tool and giving the pin the proper
width and fillets of the correct radius. If the crankshaft has straight
webs which must be finished, two tools seen at _b_ are used for facing
the webs to the correct width. During these last two operations, the
crank is supported by the roller back-rest, thus eliminating any
tendency of the work to spring.
[Illustration: Fig. 28. (A) Spherical Turning with Compound Rest. (B)
Concave Turning]
After one pin is finished in the manner described, the back-rest is
moved out of the way, the automatic stop lever raised, the carriage
shifted to the next pin, and the operation repeated. The tools are held
in position on the turret by studs, and they can be moved and other
tools quickly substituted for pins of different widths. This machine is
used for rough-turning the pins close to the required size, the
finishing operation being done in a grinder. It should be mentioned, in
passing, that many crankshafts, especially the lighter designs used in
agricultural machinery, etc., are not turned at all but are ground from
the rough.
=Spherical Turning.=--Occasionally it may be necessary to turn a
spherical surface in the lathe. Sketch _A_, Fig. 28, shows how a small
ball-shaped end can be turned on a piece held in a chuck. The lathe
carriage is adjusted so that the pin around which the compound rest
swivels is directly under the center a. The bolts which hold the swivel
are slightly loosened to allow the top slide to be turned, as indicated
by the dotted lines; this causes the tool point to move in an arc about
center _a_, and a spherical surface is turned. Light cuts must be taken
as otherwise it would be difficult to turn the slide around by hand.
[Illustration: Fig. 29. Spherical Turning Attachment for Engine Lathe]
Sketch _B_ illustrates how a concave surface can be turned. The
cross-slide is adjusted until swivel pin is in line with the lathe
centers, and the carriage is moved along the bed until the horizontal
distance between center _b_ of the swivel, and the face of the work,
equals the desired radius of the concave surface. The turning is then
done by swinging the compound rest as indicated by the dotted lines. The
slide can be turned more evenly by using the tailstock center to force
it around. A projecting bar is clamped across the end of the slide at
_d_, to act as a lever, and a centered bar is placed between this lever
and the tailstock center; then by screwing out the tailstock spindle,
the slide is turned about pivot _b_. The alignment between the swivel
pin and the lathe centers can be tested by taking a trial cut; if the
swivel pin is too far forward, the tool will not touch the turned
surface if moved past center _c_, and if the pin is too far back, the
tool will cut in on the rear side.
=Spherical Turning Attachments.=--When spherical turning must be done
repeatedly, special attachments are sometimes used. Fig. 29 shows an
attachment applied to a lathe for turning the spherical ends of
ball-and-socket joints. The height or radius of the cutting tool and,
consequently, the diameter of the turned ball, is regulated by adjusting
screw _A_. The tool is swung around in an arc, by turning handle _B_
which revolves a worm meshing with an enclosed worm-wheel. As will be
seen, the work is held in a special chuck, owing to its irregular shape.
[Illustration: Fig. 30. Attachment for Turning Spherical End of Gasoline
Engine Piston]
Another spherical turning attachment is shown in Fig. 30. This is used
for machining the ends of gasoline engine pistons. The cross-slide has
bolted to it a bar _A_ carrying a roller which is pressed against a
forming plate _B_ by a heavy spring _C_. The forming plate _B_, which is
attached to a cross-piece fastened to the ways of the lathe bed, is
curved to correspond with the radius required on the piston end, and
when the tool is fed laterally by moving the cross-slide, it follows the
curve of plate _B_. The piston is held in a special hollow chuck which
locates it in a central position and holds it rigidly.
In connection with lathe work, special attachments and tools are often
used, especially when considerable work of one class must be turned;
however, if a certain part is required in large quantities, it is
usually more economical to use some semi-automatic or automatic turning
machine, especially designed for repetition work.
=Turning with Front and Rear Tools.=--In ordinary engine lathe practice,
one tool is used at a time, but some lathes are equipped with
tool-holders at the front and rear of the carriage so that two tools can
be used simultaneously. Fig. 31 shows a detail view of a lathe in which
front and rear tools are being used. These tools are of the inserted
cutter type and the one at the rear is inverted, as the rotary movement
of the work is, of course, upward on the rear side. This particular
lathe was designed for taking heavy roughing cuts and has considerable
driving power.
[Illustration: Fig. 31. Front and Rear Tools used for Roughing]
The part shown in this illustration is a chrome-nickel steel bar which
is being roughed out to form a milling machine spindle. It is necessary
to reduce the diameter of the bar from 5-7/16 inches to 3-3/4 inches for
a length of 27 inches, because of a collar on one end. This reduction is
made in one passage of the two tools, with a feed of 1/32 inch per
revolution and a speed of 60 revolutions per minute. The use of two
tools for such heavy roughing cuts is desirable, especially when the
parts are required in large quantities, because the thrust of the cut on
one side, which tends to deflect the work, is counteracted by the thrust
on the opposite side.
[Illustration: Fig. 32. Lo-swing Lathe for Multiple Turning]
Sometimes special tool-holders are made for the lathe, so that more than
one tool can be used for turning different surfaces or diameters at the
same time, the tools being set in the proper relation to each other. The
advantage of this method has resulted in the design of a special lathe
for multiple-tool turning.
=A Multiple-tool Lathe.=--The lathe shown in Fig. 32 (which is built by
the Fitchburg Machine Works and is known as the Lo-swing) is designed
especially for turning shafts, pins and forgings not exceeding 3-1/2
inches in diameter. It has two carriages _A_ and _B_ which, in
conjunction with special tool-holders, make it possible to turn several
different diameters simultaneously. At the front of this lathe there is
an automatic stop-rod _C_ for disengaging the feed when the tools have
turned a surface to the required length. This stop-rod carries
adjustable stops _D_ which are set to correspond with shoulders, etc.,
on the work. The rod itself is also adjustable axially, so that the
tools, which are usually arranged in groups of two or more (depending
upon the nature of the work), can be disengaged at a point nearer or
farther from the headstock as may be required, owing to a variation in
the depth of center holes. For example, if it were necessary to feed a
group of tools farther toward the headstock after they had been
automatically disengaged, the entire rod with its stops would be
adjusted the required amount in that direction.
[Illustration: Fig. 33. Lo-swing Lathe arranged for Turning a Steering
Knuckle]
The gage _G_, which is attached to a swinging arm, is used to set the
stop bar with reference to a shoulder near the end of the work, when it
is necessary to finish other parts to a given distance from such a
shoulder or other surface. The use of this gage will be explained more
fully later. Cooling lubricant for the tools is supplied through the
tubes _E_. The lathe shown in the illustration is arranged for turning
Krupp steel bars. A rough bar and also one that has been turned may be
seen to the right. The plain cylindrical bar is turned to five different
diameters, by groups of tools held on both carriages.
[Illustration: Fig. 34. Plan View showing Method of driving Steering
Knuckle and Arrangement of Tools]
=Examples of Multiple Turning.=--Figs. 33 and 34 show how a Lo-swing
lathe is used for turning the steering knuckle of an automobile. Four
tools are used in this case, three cylindrical surfaces and one tapering
surface being turned at the same time. For this job, the four tools are
mounted on one carriage. The taper part is turned by the second tool
from the headstock, which is caused to feed outward as the carriage
advances by a taper attachment. This tool is held in a special holder
and bears against a templet at the rear, which is tapered to correspond
with the taper to be turned. This templet is attached to a bar which, in
turn, is fastened to a stationary bracket seen to the extreme left in
Fig. 33. This part is finished in two operations, the tool setting being
identical for each operation, except for diameter adjustments. As the
illustrations show, three of the four tools employed are used for
straight turning on different diameters, while the fourth finishes the
taper.
These pieces, which are rough drop forgings, are first reduced to the
approximate size. When it becomes necessary to grind the tools, they are
reset and those parts which have been roughed out are turned to the
finished size. The average time for the first operation, which includes
starting, stopping, turning and replacing the piece, is one minute,
while for the second operation with the finer feed, an average time of
two minutes is required. The work is driven by sleeve _S_, which fits
over the spindle and is held in position by the regular driver, as
shown. This sleeve is notched to fit the knuckle, so that the latter can
easily and quickly be replaced when finished.
One of the interesting features of this job lies in the method of
locating the shoulders on each knuckle, at the same distance from the
hole _H_ which is drilled previously, and which receives the bolt on
which the knuckle swivels when assembled in a car. As soon as the
knuckle has been placed between the centers, a close-fitting plug _P_
(Fig. 33) is inserted in this hole and the indicator arm with its
attached gage or caliper _G_ is swung up to the position shown. The
stop-rod on which the stops have been previously set for the correct
distance between the shoulders is next adjusted axially until the gage
_G_ just touches the plug _P_. The indicator is then swung out of the
way, and the piece turned. If the next knuckle were centered, say,
deeper than the previous one which would, of course, cause it to be
located nearer the headstock, obviously all the shoulders would be
located farther from the finished hole, provided the position of the
stops remained the same as before. In such a case their position would,
however, be changed by shifting the stop-rod until the gage _G_ again
touched the plug thus locating all the stops with reference to the hole.
As the adjustment of the stop-rod changes the position of the taper
templet as well as the stops, it is evident that both the shoulders and
the taper are finished the same distance from the hole in each case. The
connection of the bracket (to which the templet arm is attached) with
the stop-rod is clearly shown in Fig. 33. This bracket can either be
locked to the ways or adjusted to slide when the stop-rod is moved.
[Illustration: Fig. 35. First and Second Operations on Automobile
Transmission Shaft--Lo-swing Lathe]
The part illustrated in Fig. 35 is an automobile transmission shaft. In
this particular case, cylindrical, tapering and spherical surfaces are
turned. The upper view shows, diagrammatically, the arrangement of the
tools and work for the first operation. After the shaft is "spotted" at
_A_ for the steadyrest, the straight part _C_ and the collar _B_ are
sized with tools _S_ and _R_ which are mounted on the left-hand
carriage. A concave groove is then cut in collar _B_ by tool _R_, after
which spherical end _D_ is formed by a special attachment mounted on the
right-hand carriage. This attachment is the same, in principle, as the
regular taper-turning attachment, the substitution of a circular templet
_T_ for the straight kind used on taper work being the only practical
difference.
[Illustration: Fig. 36. Axle End turned in One Traverse of the Five
Tools shown]
After the surfaces mentioned have been finished on a number of pieces,
the work is reversed and the tools changed as shown by the lower view.
The first step in the second operation is to turn the body _E_ of the
shaft with the tool _T_ on the left-hand carriage. The taper _F_ and the
straight part _G_ are then finished, which completes the turning. It
will be noted that in setting up the machine for this second operation,
it is arranged for taper turning by simply replacing the circular
templet with the straight one shown. When this taper attachment is not
in use, the swiveling arm _M_, which is attached to a bracket, is swung
out of the way.
The method of driving this shaft is worthy of note. A dog having two
driving arms each of which bears against a pin _N_ that passes through a
hole in the spindle is used. As the ends of this pin, against which the
dog bears, are beveled in opposite directions, the pin turns in its hole
when the dog makes contact with it and automatically adjusts itself
against the two driving members of the dog. The advantage of driving by
a two-tailed dog, as most mechanics know, is in equalizing the tendency
to spring slender parts while they are being turned.
[Illustration: Fig. 37. Lathe Knurling Tool having Three Pairs of
Knurls--Coarse, Medium and Fine]
In Fig. 36 another turning operation on a lathe of this type is shown,
the work in this case being a rear axle for a motor truck. The turning
of this part is a good example of that class of work where the rapid
removal of metal is the important feature. As the engraving shows, the
stock, prior to turning, is 3-1/2 inches in diameter and it is reduced
to a minimum diameter of 1-1/16 inch. This metal is turned off with one
traverse of the carriage or by one passage of the five tools, and the
weight of the chips removed from each end of the axle is approximately
12 pounds. The time required for the actual turning is about 9 minutes,
while the total time for the operation, which includes placing the heavy
piece in the machine, turning, and removing the work from the lathe, is
12 minutes. The axle revolves, while being turned, at 110 revolutions
per minute and a feed equivalent to 1 inch of tool travel to 60
revolutions of the work is used. It will be noticed that the taper
attachment is also employed on this part, the taper being turned by the
second tool from the left. As the axle is equipped with roller bearings,
it was found desirable to finish the bearing part by a separate
operation; therefore, in the operation shown the axle is simply roughed
down rather close to the finished dimensions, leaving enough material
for a light finishing cut.
=Knurling in the Lathe.=--Knurling is done either to provide a rough
surface which can be firmly gripped by the hand or for producing an
ornamental effect. The handles of gages and other tools are often
knurled, and the thumb-screws used on instruments, etc., usually have
knurled edges. A knurled surface consists of a series of small ridges or
diamond-shaped projections, and is produced in the lathe by the use of a
tool similar to the one shown in Fig. 37, this being one of several
different designs in common use. The knurling is done by two knurls _A_
and _B_ having teeth or ridges which incline to the right on one knurl
and to the left on the opposite knurl, as shown by the end view. When
these two knurls are pressed against the work as the latter revolves,
one knurl forms a series of left-hand ridges and the other knurl
right-hand ridges, which cross and form the diamond-shaped knurling
which is generally used.
If the surface to be knurled is wider than the knurls, the power feed of
the lathe should be engaged and the knurling tool be traversed back and
forth until the diamond-shaped projections are well formed. To prevent
forming a double set of projections, feed the knurl in with considerable
pressure at the start, then partially relieve the pressure before
engaging the power feed. Use oil when knurling.
The knurls commonly used for lathe work have spiral teeth and ordinarily
there are three classes, known as coarse, medium and fine. The medium
pitch is generally used. The teeth of coarse knurls have a spiral angle
of 36 degrees and the pitch of the knurled cut (measured parallel to the
axis of the work) should be about 8 per inch. For medium knurls, the
spiral angle is 29-1/2 degrees and the pitch, measured as before, is 12
per inch. For fine knurls, the spiral angle is 25-3/4 degrees and the
pitch 20 per inch. The knurls should be about 3/4 inch in diameter and
3/8 inch wide. When made to these dimensions, coarse knurls have 34
teeth; medium, 50 teeth; and fine knurls, 80 teeth.
[Illustration: Fig. 38. Hendey Relieving Attachment applied to a Lathe]
The particular tool illustrated in Fig. 37 has three pairs of knurls of
coarse, medium and fine pitch. These are mounted in a revolving holder
which not only serves to locate the required set of knurls in the
working position, but enables each knurl to bear against the surface
with equal pressure. Concave knurls are sometimes used for knurling
rounded edges on screw heads, etc.
=Relieving Attachment.=--Some lathes, particularly those used in
toolrooms, are provided with relieving attachments which are used for
"backing off" the teeth of milling cutters, taps, hobs, etc. If a
milling cutter of special shape is to be made, the cutter blank is first
turned to the required form with a special tool having a cutting edge
that corresponds with the shape or profile of the cutter to be made. The
blank is then fluted or gashed to form the teeth, after which the tops
of the teeth are relieved or backed off to provide clearance for the
cutting edges. The forming tool used for turning the blank is set to
match the turned surface, and the teeth are backed off as the result of
a reciprocating action imparted to the toolslide by the relieving
attachment. The motion of the toolslide is so adjusted that the tool
will meet the front of each tooth and the return movement begin promptly
after the tool leaves the back end of the tooth.
[Illustration: Fig. 39. Relieving a Formed Cutter]
These attachments differ somewhat in their construction and arrangement
but the principle of their operation is similar. Fig. 38 shows a Hendey
relieving attachment applied to a lathe. A bracket carrying the gearing
_A_ through which the attachment is driven is mounted upon the main gear
box of the lathe, and the special slide _B_, which is used when
relieving, is placed on the cross-slide after removing the regular
compound rest. The gears at _A_ are changed to suit the number of flutes
or gashes in the cutter, tap or whatever is to be relieved. If we assume
that the work is a formed milling cutter having nine teeth, then with
this particular attachment, a gear having 90 teeth would be placed on
the "stud" and a 40-tooth gear on the cam-shaft, the two gears being
connected by a 60-tooth intermediate gear. With this combination of
gearing, the toolslide would move in and out nine times for each
revolution of the work, so that the tool could back off the top of each
tooth. (The gearing to use for various numbers of flutes is shown by an
index plate on the attachment.) The amount of relief is varied to suit
the work being done, by means of a toothed coupling which makes it
possible to change the relative position between the eccentric which
actuates the toolslide and the cam lever, thereby lengthening or
shortening the reciprocating travel of the tool.
[Illustration: Fig. 40. Relieving Side of Angular Milling Cutter]
=Application of Relieving Attachment.=--Some typical examples of the
kind of work for which the relieving attachment is used are shown in
Figs. 39 to 42, inclusive. Fig. 39 shows how a formed milling cutter is
relieved. The toolslide is set at right angles to the axis of the work,
and the tool moves in as each tooth passes, and out while crossing the
spaces or flutes between the teeth. As the result of this movement, the
tops of the teeth are backed off eccentrically but the form or shape is
the same from the front to the back of the tooth; hence, a cutter that
has been relieved in this way can be ground repeatedly without changing
the profile of the teeth, provided the faces are ground so as to lie in
a radial plane.
When relieving, the cutting speed should be much less than when turning
in order to give the toolslide time to operate properly. A maximum of
180 teeth per minute is recommended, and, if wide forming tools are
used, it might be advisable to reduce the speed so low that only 8 teeth
per minute would be relieved. It is also essential to use a tool having
a keen edge, and the toolslide should work freely but be closely
adjusted to the dovetail of the lower slide. Before beginning to back
off the teeth, it is a good plan to color the work either by heating it
or dipping into a strong solution of copper sulphate. This will enable
one to see plainly the cutting action of the tool in order to stop
relieving at the proper time.
[Illustration: Fig. 41. Relieving a Right-hand Tap]
Fig. 40 shows a method of relieving the teeth of an angular cutter. For
an operation of this kind the toolslide is swiveled around at right
angles to the side that is to be relieved. By the use of an additional
universal joint and bearing to permit the toolslide to be swung to a
90-degree angle, the teeth of counterbores, etc., can be relieved on the
ends. When the attachment is used for relieving inside work, such as
hollow mills and threading dies, the eccentric which controls the travel
of the toolslide is set so that the relieving movement is away from the
axis of the cutter instead of toward it. This change is made by the
toothed coupling previously referred to, which connects the cam lever
and oscillating shaft, the latter being turned beyond the zero mark in a
clockwise direction as far as is necessary to obtain the desired amount
of travel. For internal work it is also necessary to change the position
of the opposing spring of the toolslide, so that it will press against
the end of the slide and prevent the tool from jumping into the work.
[Illustration: Fig. 42. Relieving a Hob having Spiral Flutes]
Fig. 41 shows how a right-hand tap is relieved. The ordinary practice is
to first set the tool the same as for cutting a thread. The motion of
the toolslide is then adjusted so that the tool on the forward stroke
will meet the front of each tooth, and start back as soon as the tool
leaves the end of the land or top of the tooth. Taps having a left-hand
thread can be relieved by two different methods. With the first method
the cut starts at the cutting edge of each tooth, and ends at the
"heel," the tool moving in toward the center of the work. With the
second method, the cut begins at the heel and discontinues at the
cutting edge, the tool being drawn away from the work during the cut.
When using the first method the tap must be placed with the point toward
the headstock, the shank end being supported by the tailstock center.
This is done by providing an extension or blank end at the point of the
tap long enough to hold the driving dog. With the second method, the tap
is held between centers the same as one having a right-hand thread, but
the travel of the toolslide is set the same as for inside relief.
=Relieving Hobs or Taps Having Spiral Flutes.=--With this attachment,
taps or hobs having "spiral" or helical flutes can also be relieved. (A
spiral flute is preferable to one that is parallel to the axis, because
with the former the tool has cutting edges which are square with the
teeth; this is of especial importance when the lead of the hob or tap
thread is considerable.) When relieving work having spiral flutes (as
illustrated in Fig. 42), the lead of the spiral and the gears necessary
to drive the attachment are first determined. After the attachment is
geared for the number of flutes and to compensate for the spiral, the
lead-screw is engaged and the backing-off operation is performed the
same as though the flutes were straight. The carriage should not be
disengaged from the lead-screw after starting the cut, the tool being
returned by reversing the lathe.
When gearing the attachment for relieving a tap or hob having spiral
flutes, the gears are not selected for the actual number of flutes
around the circumference but for a somewhat larger number which depends
upon the lead of the hob thread and the lead of the spiral flutes. Let
us assume that a hob has 6 spiral flutes and that the attachment is
geared for that number. The result would be that as the tool advanced
along the thread, it would not keep "in step" with the teeth because the
faces of the teeth lie along a spiral (or helix which is the correct
name for this curve); in other words, the tool would soon be moving in
too late to begin cutting at the proper time, and to compensate for
this, the attachment is geared so that the tool will make a greater
number of strokes per revolution of the work than the actual number of
flutes around the circumference.
With this attachment, the two gears listed on the index plate for the
actual number of flutes are selected, and then two compensating gears
are added, thus forming a compound train of gearing. The ratio _R_ of
these compensating gears is determined as follows:
_r_ + 1
R = -------
_r_
in which
_r_ = _L_ ÷ _l_;
_L_ = lead of spiral;
_l_ = lead of hob thread.
For example, if a hob has a pitch circumference of 3.25, a single thread
of 0.75 inch lead, and 6 spiral flutes, what compensating gears would be
required?
The lead _L_ of the spiral flutes is first determined by dividing the
square of the circumference _C_ of the hob at the pitch line by the lead
_l_ of the hob thread. Thus lead _L_ = _C^2_/_l_, or, in this case, _L_
= 3.25^2/0.75 = 14 inches, approximately. Then _r_ = 14 ÷ 0.75 = 18-2/3.
Inserting these values in the formula for ratio R,
18-2/3 + 1 19-2/3 19-2/3 × 3 59
_R_ = ---------- = ------ = ---------- = --
18-2/3 18-2/3 18-2/3 × 3 56
Hence, the compensating gears will have 56 and 59 teeth, respectively,
the latter being the driver. As the gears for 6 flutes listed on the
regular index plate are, stud-gear 60 teeth, cam-shaft gear 40 teeth,
the entire train of gears would be as follows: Gear on stud, 60;
_driven_ intermediate gear, 56; _driving_ intermediate gear, 59;
cam-shaft gear, 40. It will be understood that the position of the
driving gears or the driven gears can be transposed without affecting
the ratio.
=Classes of Fits Used in Machine Construction.=--In assembling machine
parts it is necessary to have some members fit together tightly, whereas
other parts such as shafts, etc., must be free to move or revolve with
relation to each other. The accuracy required for a fitting varies for
different classes of work. A shaft that revolves in its bearing must be
slightly smaller than the bearing so that there will be room for a film
of lubricant. A crank-pin that must be forced into the crank-disk is
made a little larger in diameter than the hole, to secure a tight fit.
When a very accurate fitting between two cylindrical parts that must be
assembled without pressure is required, the diameter of the inner member
is made as close to the diameter of the outer member as is possible. In
ordinary machine construction, five classes of fits are used, _viz_;
running fit, push fit, driving fit, forced fit and shrinkage fit. The
running fit, as the name implies, is employed when parts must rotate;
the push fit is not sufficiently free to rotate; the other classes
referred to are used for assembling parts that must be held in fixed
positions.
=Forced Fits.=--This is the term used when a pin, shaft or other
cylindrical part is forced into a hole of slightly smaller diameter, by
the use of a hydraulic press or other means. As a rule, forced fits are
restricted to parts of small and medium size, while shrinkage fits have
no such limitations and are especially applicable when a maximum "grip"
is desired, or when (as in the construction of ordnance) accurate
results as to the intensity of stresses produced in the parts united are
required. The proper allowance for a forced fit depends upon the mass of
metal surrounding the hole, the size of the work, the kind and quality
of the material of which the parts are composed and the smoothness and
accuracy of the pin and bore. When a pin or other part is pressed into a
hole a second time, the allowance for a given tonnage should be
diminished somewhat because the surface of the bore is smoother and the
metal more compact. The pressure required in assembling a forced fit
will also vary for cast hubs of the same size, if they are not uniform
in hardness. Then there is the personal factor which is much in evidence
in work of this kind; hence, data and formulas for forced fit allowances
must be general in their application.
=Allowance for Forced Fits.=--The allowance per inch of diameter usually
ranges from 0.001 inch to 0.0025 inch, 0.0015 being a fair average.
Ordinarily, the allowance per inch decreases as the diameter increases;
thus the total allowance for a diameter of 2 inches might be 0.004 inch,
whereas for a diameter of 8 inches the total allowance might not be over
0.009 or 0.010 inch. In some shops the allowance is made practically the
same for all diameters, the increased surface area of the larger sizes
giving sufficient increase in pressure. The parts to be assembled by
forced fits are usually made cylindrical, although sometimes they are
slightly tapered. The advantages of the taper form are that the
possibility of abrasion of the fitted surfaces is reduced; that less
pressure is required in assembling; and that the parts are more readily
separated when renewal is required. On the other hand, the taper fit is
less reliable, because if it loosens, the entire fit is free with but
little axial movement. Some lubricant, such as white lead and lard oil
mixed to the consistency of paint, should be applied to the pin and bore
before assembling, to reduce the tendency of abrasion.
Allowances for Different Classes of Fits
(Newall Engineering Co.)
+-----+--------------------------------------------------------------+
| | Tolerances in Standard Holes[1] |
|Class+------------+---------+---------+---------+---------+---------+
| | Nominal | Up to | 9/16"-1"| 1-1/16"-| 2-1/16"-| 3-1/16"-|
| | Diameters | 1/2" | | 2" | 3" | 4" |
+-----+------------+---------+---------+---------+---------+---------+
| | High Limit | +0.0002 | +0.0005 | +0.0007 | +0.0010 | +0.0010 |
| A | Low Limit | -0.0002 | -0.0002 | -0.0002 | -0.0005 | -0.0005 |
| | Tolerance | 0.0004 | 0.0007 | 0.0009 | 0.0015 | 0.0015 |
+-----+------------+---------+---------+---------+---------+---------+
| | High Limit | +0.0005 | +0.0007 | +0.0010 | +0.0012 | +0.0015 |
| B | Low Limit | -0.0005 | -0.0005 | -0.0005 | -0.0007 | -0.0007 |
| | Tolerance | 0.0010 | 0.0012 | 0.0015 | 0.0019 | 0.0022 |
+-----+------------+---------+---------+---------+---------+---------+
| Allowances for Forced Fits |
+-----+------------+---------+---------+---------+---------+---------+
| | High Limit | +0.0010 | +0.0020 | +0.0040 | +0.0060 | +0.0080 |
| F | Low Limit | +0.0005 | +0.0015 | +0.0030 | +0.0045 | +0.0060 |
| | Tolerance | 0.0005 | 0.0005 | 0.0010 | 0.0015 | 0.0020 |
+-----+------------+---------+---------+---------+---------+---------+
| Allowances for Driving Fits |
+-----+------------+---------+---------+---------+---------+---------+
| | High Limit | +0.0005 | +0.0010 | +0.0015 | +0.0025 | +0.0030 |
| D | Low Limit | +0.0002 | +0.0007 | +0.0010 | +0.0015 | +0.0020 |
| | Tolerance | 0.0003 | 0.0003 | 0.0005 | 0.0010 | 0.0010 |
+-----+------------+---------+---------+---------+---------+---------+
| Allowances for Push Fits |
+-----+------------+---------+---------+---------+---------+---------+
| | High Limit | -0.0002 | -0.0002 | -0.0002 | -0.0005 | -0.0005 |
| P | Low Limit | -0.0007 | -0.0007 | -0.0007 | -0.0010 | -0.0010 |
| | Tolerance | 0.0005 | 0.0005 | 0.0005 | 0.0005 | 0.0005 |
+-----+------------+---------+---------+---------+---------+---------+
| Allowances for Running Fits[2] |
+-----+------------+---------+---------+---------+---------+---------+
| | High Limit | -0.0010 | -0.0012 | -0.0017 | -0.0020 | -0.0025 |
| X | Low Limit | -0.0020 | -0.0027 | -0.0035 | -0.0042 | -0.0050 |
| | Tolerance | 0.0010 | 0.0015 | 0.0018 | 0.0022 | 0.0025 |
| | High Limit | -0.0007 | -0.0010 | -0.0012 | -0.0015 | -0.0020 |
| Y | Low Limit | -0.0012 | -0.0020 | -0.0025 | -0.0030 | -0.0035 |
| | Tolerance | 0.0005 | 0.0010 | 0.0013 | 0.0015 | 0.0015 |
| | High Limit | -0.0005 | -0.0007 | -0.0007 | -0.0010 | -0.0010 |
| Z | Low Limit | -0.0007 | -0.0012 | -0.0015 | -0.0020 | -0.0022 |
| | Tolerance | 0.0002 | 0.0005 | 0.0008 | 0.0010 | 0.0012 |
+-----+------------+---------+---------+---------+---------+---------+
[1] Tolerance is provided for holes, which ordinary standard reamers can
produce, in two grades, Classes A and B, the selection of which is a
question for the user's decision and dependent upon the quality of the
work required; some prefer to use Class A as working limits and Class B
as inspection limits.
[2] Running fits, which are the most commonly required, are divided into
three grades: Class X for engine and other work where easy fits are
wanted; Class Y for high speeds and good average machine work; Class Z
for fine tool work.
=Pressure for Forced Fits.=--The pressure required for assembling
cylindrical parts depends not only upon the allowance for the fit, but
also upon the area of the fitted surfaces, the pressure increasing in
proportion to the distance that the inner member is forced in. The
approximate ultimate pressure in pounds can be determined by the use of
the following formula in conjunction with the accompanying table of
"Pressure Factors."
=Pressure Factors=
+-----+-----++-----+-----++-----+-----++------+------++------+------+
|Diam-|Pres-||Diam-|Pres-||Diam-|Pres-||Diam- |Pres- ||Diam- |Pres- |
|eter,|sure ||eter,|sure ||eter,|sure ||eter, |sure ||eter, |sure |
|In- |Fac- ||In- |Fac- ||In- |Fac- ||In- |Fac- ||In- |Fac- |
|ches | tor ||ches | tor ||ches | tor ||ches |tor ||ches |tor |
+-----+-----++-----+-----++-----+-----++------+------++------+------+
|1 | 500 ||3-1/2| 132 ||6 | 75 || 9 | 48.7 ||14 | 30.5 |
|1-1/4| 395 ||3-3/4| 123 ||6-1/4| 72 || 9-1/2| 46.0 ||14-1/2| 29.4 |
|1-1/2| 325 ||4 | 115 ||6-1/2| 69 ||10 | 43.5 ||15 | 28.3 |
|1-3/4| 276 ||4-1/4| 108 ||6-3/4| 66 ||10-1/2| 41.3 ||15-1/2| 27.4 |
|2 | 240 ||4-1/2| 101 ||7 | 64 ||11 | 39.3 ||16 | 26.5 |
|2-1/4| 212 ||4-3/4| 96 ||7-1/4| 61 ||11-1/2| 37.5 ||16-1/2| 25.6 |
|2-1/2| 189 ||5 | 91 ||7-1/2| 59 ||12 | 35.9 ||17 | 24.8 |
|2-3/4| 171 ||5-1/4| 86 ||7-3/4| 57 ||12-1/2| 34.4 ||17-1/2| 24.1 |
|3 | 156 ||5-1/2| 82 ||8 | 55 ||13 | 33.0 ||18 | 23.4 |
|3-1/4| 143 ||5-3/4| 78 ||8-1/2| 52 ||13-1/2| 31.7 ||.... | .... |
+-----+-----++-----+-----++-----+-----++------+------++------+------+
Assuming that _A_ = area of fitted surface; _a_ = total allowance in
inches; _P_ = ultimate pressure required, in tons; _F_ = pressure factor
based upon assumption that the diameter of the hub is twice the
diameter of the bore, that the shaft is of machine steel, and the hub of
cast iron, then,
_A_ × _a_ × _F_
_P_ = ---------------
2
_Example:_--What will be the approximate pressure required for forcing a
4-inch machine steel shaft having an allowance of 0.0085 inch into a
cast-iron hub 6 inches long?
_A_ = 4 × 3.1416 × 6 = 75.39 square inches;
_F_, for a diameter of 4 inches, = 115 (see table of "Pressure
Factors"). Then,
_P_ = (75.39 × 0.0085 × 115)/2 = 37 tons, approximately.
=Allowance for Given Pressure.=--By transposing the preceding formula,
the approximate allowance for a required ultimate tonnage can be
determined. Thus, _a_ = 2_P_ ÷ _AF_. The average ultimate pressure in
tons commonly used ranges from 7 to 10 times the diameter in inches.
Assuming that the diameter of a machine steel shaft is 4 inches and an
ultimate pressure of about 30 tons is desired for forcing it into a
cast-iron hub having a length of 5-1/2 inches, what should be the
allowance?
_A_ = 4 × 3.1416 × 5-1/2 = 69 square inches,
_F_, for a diameter of 4 inches, = 115. Then,
2 × 30
_a_ = -------- = 0.0075 inch.
69 × 115
=Shrinkage Fits.=--When heat is applied to a piece of metal, such as
iron or steel, as is commonly known, a certain amount of expansion takes
place which increases as the temperature is increased, and also varies
somewhat with different kinds of metal, copper and brass expanding more
for a given increase in temperature than iron and steel. When any part
which has been expanded by the application of heat is cooled, it
contracts and resumes its original size. This expansive property of
metals has been taken advantage of by mechanics in assembling various
machine details. A cylindrical part which is to be held in position by a
shrinkage fit is first turned a few thousandths of an inch larger than
the hole; the diameter of the latter is then increased by heating, and
after the part is inserted, the heated outer member is cooled, causing
it to grip the pin or shaft with tremendous pressure.
General practice seems to favor a smaller allowance for shrinkage fits
than for forced fits, although in many shops the allowances are
practically the same in each case, and for some classes of work,
shrinkage allowances exceed those for forced fits. In any case, the
shrinkage allowance varies to a great extent with the form and
construction of the part which has to be shrunk into place. The
thickness or amount of metal around the hole is the most important
factor. The way in which the metal is distributed also has an influence
on the results. Shrinkage allowances for locomotive driving wheel tires
adopted by the American Railway Master Mechanics Association are as
follows:
Center diameter, inches 38 44 50 56 62 66
Allowance, inches 0.040 0.047 0.053 0.060 0.066 0.070
Whether parts are to be assembled by forced or shrinkage fits depends
upon conditions. For example, to press a driving wheel tire over its
wheel center, without heating, would ordinarily be a rather awkward and
difficult job. On the other hand, pins, etc., are easily and quickly
forced into place with a hydraulic press and there is the additional
advantage of knowing the exact pressure required in assembling, whereas
there is more or less uncertainty connected with a shrinkage fit, unless
the stresses are calculated. Tests to determine the difference in the
quality of shrinkage and forced fits showed that the resistance of a
shrinkage fit to slippage was, for an axial pull, 3.66 times greater
than that of a forced fit, and in rotation or torsion, 3.2 times
greater. In each comparative test, the dimensions and allowances were
the same.
The most important point to consider when calculating shrinkage fits is
the stress in the hub at the bore, which depends chiefly upon the
shrinkage allowance. If the allowance is excessive, the elastic limit of
the material will be exceeded and permanent set will occur, or, in
extreme cases, the ultimate strength of the metal will be exceeded and
the hub will burst.
CHAPTER IV
THREAD CUTTING IN THE LATHE
When threads are cut in the lathe a tool _t_ is used (see Fig. 2),
having a point corresponding to the shape of the thread, and the
carriage is moved along the bed a certain distance for each revolution
of the work (the distance depending on the number of threads to the inch
being cut) by the lead-screw _S_ which is rotated by gears _a_, _b_ and
_c_, which receive their motion from the spindle. As the amount that the
carriage travels per revolution of the work, and, consequently, the
number of threads per inch that is cut, depends on the size of the gears
_a_ and _c_ (called change gears) the latter have to be changed for
cutting different threads. The proper change gears to use for cutting a
given number of threads to the inch is ordinarily determined by
referring to a table or "index plate" _I_ which shows what the size of
gears _a_ and _c_ should be, or the number of teeth each should have,
for cutting any given number of threads per inch.
[Illustration: Fig. 1. Measuring Number of Threads per Inch--Setting
Thread Tool]
[Illustration: Fig. 2. Plan and Elevations of Engine Lathe]
=Selecting the Change Gears for Thread Cutting.=--Suppose a V-thread is
to be cut on the end of the bolt _B_, Fig. 2, having a diameter of 1-1/4
inch and seven threads per inch of length, as shown at _A_ in Fig. 1,
which is the standard number of threads per inch for that diameter.
First the change gears to use are found on plate _I_ which is shown
enlarged in Fig. 3. This plate has three columns: The first contains
different numbers of threads to the inch, the second the size gear to
place on the "spindle" or "stud" at _a_ (Fig. 2) for different threads,
and the third the size of gear _c_ for the lead-screw. As the thread
selected as an example has 7 threads per inch, gear _a_ should have 48
teeth, this being the number given in the second column opposite figure
7 in the first. By referring to the last column, we find that the
lead-screw gear should have 84 teeth. These gears are selected from an
assortment provided with the lathe and they are placed on the spindle
and lead-screw, respectively.
[Illustration: Fig. 3. Index Plate showing Gear Changes for Threading]
Intermediate gear _b_ does not need to be changed as it is simply an
"idler" for connecting gears _a_ and _c_. Gear _b_ is mounted on a
swinging yoke _Y_ so that it can be adjusted to mesh properly with
different gear combinations; after this adjustment is made, the lathe is
geared for cutting 7 threads to the inch. (The change gears of many
modern lathes are so arranged that different combinations are obtained
by simply shifting a lever. A lathe having this quick-change gear
mechanism is described in the latter part of this chapter.) The work _B_
is placed between the centers just as it would be for turning, with the
end to be threaded turned to a diameter of 1-1/4 inch, which is the
outside diameter of the thread.
=The Thread Tool.=--The form of tool used for cutting a V-thread is
shown at _A_, Fig. 4. The end is ground V-shaped and to an angle of 60
degrees, which corresponds to the angle of a standard V-thread. The
front or flank, _f_ of the tool is ground back at an angle to provide
clearance, but the top is left flat or without slope. As it is very
important to grind the end to exactly 60 degrees, a gage _G_ is used,
having 60-degree notches to which the tool-point is fitted. The tool is
clamped in the toolpost as shown in the plan view, Fig. 2, square with
the work, so that both sides of the thread will be cut to the same angle
with the axis of the work. A very convenient way to set a thread tool
square is illustrated at _B_, Fig. 1. The thread gage is placed against
the part to be threaded, as shown, and the tool is adjusted until the
angular sides of the point bear evenly in the 60-degree notch of the
gage. The top of the tool point should be at the same height as the
lathe centers, as otherwise the angle of the thread will not be correct.
[Illustration: Fig. 4. Thread Tools and Gage for testing Angle of End]
=Cutting the Thread.=--The lathe is now ready for cutting the thread.
This is done by taking several cuts, as indicated at _A_, _B_, _C_ and
_D_ in Fig. 5, the tool being fed in a little farther for each
successive cut until the thread is finished. When these cuts are being
taken, the carriage is moved along the bed, as previously explained, by
the lead-screw _S_, Fig. 2. The carriage is engaged with the lead-screw
by turning lever _u_ which causes the halves of a split nut to close
around the screw. The way a lathe is handled when cutting a thread is as
follows: After the lathe is started, the carriage is moved until the
tool-point is slightly beyond the right end of the work, and the tool is
fed in far enough to take the first cut which, ordinarily, would be
about 1/16 inch deep. The carriage is then engaged with the lead-screw,
by operating lever _u_, and the tool moves to the left (in this case 1/7
inch for each revolution of the work) and cuts a winding groove as at
_A_, Fig. 5. When the tool has traveled as far as the thread is wanted,
it is withdrawn by a quick turn of cross-slide handle _e_, and the
carriage is returned to the starting point for another cut. The tool is
then fed in a little farther and a second cut is taken as at _B_, Fig.
5, and this operation is repeated as at _C_ and _D_ until a "full"
thread is cut or until the top of the thread is sharp. The thread is
then tested for size but before referring to this part of the work, the
way the carriage is returned to the starting point after each cut should
be explained.
[Illustration: Fig. 5. Thread is formed by taking a Number of Successive
Cuts]
When the tool is withdrawn at the end of the first cut, if the carriage
is disengaged from the lead-screw and returned by hand, the tool may or
may not follow the first cut when the carriage is again engaged with the
lead-screw. If the number of threads to the inch being cut is a multiple
of the number on the lead-screw _S_, then the carriage can be returned
by hand and engaged with the lead-screw at random and the tool will
follow the first cut. For example, if the lead-screw has six threads per
inch, and 6, 12, 18 or any number of threads is being cut that is a
multiple of six, the carriage can be engaged at any time and the tool
will always follow the original cut. This is not the case, however, when
the number of threads being cut is not a multiple of the number on the
lead-screw.
One method of bringing the carriage back to the starting point, when
cutting threads which are not multiples, is to reverse the lathe (by
shifting the overhead driving belts) in order to bring the tool back to
the starting point without disengaging the carriage; in this way the
tool is kept in the same relation to the work, and the carriage is not
disengaged from the lead-screw until the thread is finished. This is a
good method when cutting short threads having a length of say two or
three inches; but when they are longer, and especially when the diameter
is comparatively large (which means a slower speed), it is rather slow
as considerable time is wasted while the tool is moving back to its
starting point. This is due to the fact that the carriage is moved
slowly by the lead-screw, but when disengaged, it can be traversed
quickly by turning handle _d_, Fig. 2.
A method of returning the carriage by hand when the number of threads
being cut is not a multiple of the number on the lead-screw is as
follows: The tool is moved a little beyond the right end of the work and
the carriage or split nut is engaged with the lead-screw. The lathe is
then turned forward by hand to take up any lost motion, and a line is
made on the lathe bed showing the position of the carriage. The
positions of the spindle and lead-screw are also marked by chalking a
tooth on both the spindle and lead-screw gears, which happens to be
opposite a corner or other point on the bed. After a cut is taken, the
carriage is returned by hand to the original starting point as shown by
the line on the bed, and is again engaged when the chalk marks show that
the spindle and lead-screw are in their original position; the tool will
then follow the first cut. If the body of the tailstock is moved against
the bridge of the carriage before starting the first cut, the carriage
can be located for each following cut by moving it back against the
tailstock, and it will not be necessary to have a line on the bed.
[Illustration: Fig. 6. Indicator used when Cutting Threads]
=Indicator or Chasing Dial for Catching Threads.=--On some lathes there
is an indicator for "catching threads," as this is called in shop
language. This is a simple device attached to the carriage and consists
of a graduated dial _D_ and a worm-wheel _W_ (see Figs. 2 and 6) which
meshes with the lead-screw, so that the dial is revolved by the
lead-screw when the carriage is stationary, and when the carriage is
moved by the screw, the dial remains stationary. The indicator is used
by engaging the carriage when one of the graduation lines is opposite
the arrow mark; after a cut is taken the carriage is returned by hand
and when one of the graduation lines again moves opposite the arrow, the
half-nuts are thrown into mesh, as before, and this is repeated for each
successive cut, thus causing the tool to always come right with the
thread. If the number of threads per inch is even, engagement can be
made when any line is opposite the arrow, but for odd numbers such as 3,
7, 9, 11, etc., one of the four long or numbered lines must be used. Of
course, if the thread being cut is a multiple of the number on the
lead-screw, engagement can be made at any time, as previously
mentioned.
=Principle of the Thread Indicator.=--The principle upon which the
thread indicator operates is as follows: The number of teeth in
worm-wheel _W_ is some multiple of the number of threads per inch of the
lead-screw, and the number of teeth in the worm-wheel, divided by the
pitch of the screw, equals the number of graduations on the dial. For
example, if the lead-screw has six threads per inch, the worm-wheel
could have twenty-four teeth, in which case the dial would have four
divisions, each representing an inch of carriage travel, and by
sub-dividing the dial into eighths (as shown) each line would correspond
to 1/2 inch of travel. The dial, therefore, would enable the carriage to
be engaged with the lead-screw at points equal to a travel of one-half
inch. To illustrate the advantage of this suppose ten threads per inch
are being cut and (with the lathe stationary) the carriage is disengaged
and moved 1/6 inch or one thread on the lead-screw; the tool point will
also have moved 1/6 inch, but it will not be opposite the next thread
groove in the work as the pitch is 1/10 inch. If the carriage is moved
another thread on the lead-screw, or 2/6 inch, the tool will still be
out of line with the thread on the work, but when it has moved three
threads, or 1/2 inch, the tool will then coincide with the original cut
because it has passed over exactly five threads. This would be true for
any number of threads per inch that is divisible by 2. If the thread
being cut had nine threads per inch or any other odd number, the tool
would only coincide with the thread at points 1 inch apart. Therefore,
the carriage can only be engaged when one of the four graduations
representing an inch of travel is opposite the arrow, when cutting odd
threads; whereas even numbers can be "caught" by using any one of the
eight lines.
This indicator can also be used for "catching" fractional threads. As an
illustration, suppose 11-1/2 threads per inch are to be cut, and the
carriage is engaged for the first cut when graduation line 1 is opposite
the arrow; engagement would then be made for each successive cut, when
either line 1 or 3 were opposite the arrow, or in other words at spaces
equal to a carriage movement of 2 inches. As the use of the indicator
when cutting fractional threads is liable to result in error, it is
better to keep the half-nuts in engagement and return the carriage by
reversing the lathe.
=Replacing Sharpened Thread Tool.=--If it is necessary to sharpen the
thread tool before the thread is finished, it should be reset square
with the work by testing with the thread gage as at _B_, Fig. 1. The
carriage is then engaged with the lead-screw and the lathe is turned
forward to bring the tool opposite the partly finished thread and also
to take up any backlash or lost motion in the gears or half-nut. If the
tool-point is not in line with the thread groove previously cut, it can
be shifted sidewise by feeding the compound rest _E_ in or out, provided
the latter is set in an angular position as shown in the plan view, Fig.
2.
If the thread tool is ground flat on the top as at _A_, Fig. 4, it is
not a good tool for removing metal rapidly as neither of its two cutting
edges has any slope. In order to give each cutting edge a backward
slope, it would be necessary to grind the top surface hollow or concave,
which would be impracticable. When a course thread is to be cut, a tool
shaped as at _B_ can be used to advantage for rough turning the thread
groove, which is afterward finished to the correct depth and angle by
tool _A_. This roughing tool is ground with a backward slope from the
point and the latter is rounded to make it stronger.
=Use of Compound Rest for Thread Cutting.=--Another form of thread tool
is shown at _A_, Fig. 7, which is very good for cutting V-threads
especially of coarse pitch. When this tool is used, the compound rest
_E_ is set to an angle of 30 degrees, as shown, and it is fed in for the
successive cuts by handle _w_ in the direction indicated by the arrow.
It will be seen that the point a of the tool moves at an angle of 60
degrees with the axis of the work, thus forming one side of the thread,
and the cutting edge _a--b_, which can be set as shown at _B_, forms the
opposite side and does all the cutting. As this edge is given a backward
slope, as shown, it cuts easily and enables threading operations to be
performed quickly. Threads cut in this way are often finished by taking
a light cut with a regular thread tool. The cutting edge _a--b_ is
ground to an angle of 60 degrees (or slightly less, if anything) with
the side, as shown by sketch _A_.
When cutting threads in steel or wrought iron, some sort of lubricant is
usually applied to the tool to preserve the cutting end and give a
smooth finish to the thread. Lard oil or a mixture of equal parts of
lard oil and paraffin oil are often used for this purpose. If the thread
is small, the lubricant may be applied from an ordinary oil can, but
when cutting comparatively large threads, it is better to have a stream
of oil constantly playing upon the tool-point. This constant flow may be
obtained by mounting a can having a spout leading to the tool, on a
bracket at the rear of the carriage.
[Illustration: Fig. 7. Cutting Thread by using Compound Rest]
[Illustration: Fig. 8. (A) V-thread. (B) U. S. Standard Thread. (C)
Square Thread. (D) Left-hand Thread. (E) Double Square Thread. (F)
Triple Square Thread]
=Threads Commonly Used.=--Three forms of threads or screws which are in
common use are shown in Fig. 8; these are the V-thread (_A_), the U. S.
standard (_B_), and the square thread (_C_). The shapes of these threads
are shown by the sectioned parts. The V-thread has straight sides which
incline at an angle of 60 degrees with each other and at the same angle
with the axis of the screw. The U. S. standard thread is similar to the
V-thread except that the top of the thread and bottom of the groove is
left flat, as shown, and the width of these flats is made equal to 1/8
of the pitch. The square thread is square in section, the width _a_,
depth _b_ and space _c_ being all equal. All of these threads are
right-hand, which means that the grooves wind around to the right so
that a nut will have to be turned toward the right to enter it on the
thread. A left-hand thread winds in the other direction, as shown at
_D_, and a nut is screwed on by turning it to the left.
=Multiple Threads.=--Threads, in addition to being right-and
left-handed, are single, as at _A_, _B_, _C_ and _D_, double, as at _E_,
and triple, as at _F_, and for certain purposes quadruple threads or
those of a higher multiple are employed. A double thread is different
from a single thread in that it has two grooves, starting diametrically
opposite, whereas a triple thread has three grooves cut as shown at _F_.
The object of these multiple threads is to obtain an increase in lead
without weakening the screw. For example, the threads shown at _C_ and
_E_ have the same pitch _p_ but the lead _l_ of the double-threaded
screw is twice that of the one with a single thread so that a nut would
advance twice as far in one revolution, which is often a very desirable
feature. To obtain the same lead with a single thread, the pitch would
have to be double, thus giving a much coarser thread, which would weaken
the screw, unless its diameter were increased. (The lead is the distance
_l_ that one thread advances in a single turn, or the distance that a
nut would advance in one turn, and it should not be confused with the
pitch _p_, which is the distance between the centers of adjacent
threads. Obviously the lead and pitch of a single thread are the same.)
=Cutting a U. S. Standard Thread.=--The method of cutting a U. S.
standard thread is the same as described for a V-thread, so far as
handling the lathe is concerned. The thread tool must correspond, of
course, to the shape of a U. S. standard thread. This tool is first
ground to an angle of 60 degrees, as it would be for cutting a V-thread,
and then the point is made flat as shown in Fig. 9. As will be recalled,
the width of this flat should be equal to 1/8 of the pitch. By using a
gage like the one shown at _G_, the tool can easily be ground for any
pitch, as the notches around the periphery of the gage are marked for
different pitches and the tool-point is fitted into the notch
corresponding to the pitch wanted. If such a gage is not available, the
width of the flat at the point can be tested by using, as a gage, a U.
S. standard tap of the same pitch as the thread to be cut.
When cutting the thread, the tool is set square with the blank, and a
number of successive cuts are taken, the tool being fed in until the
width w of the flat at the top of the thread is equal to the width at
the bottom. The thread will then be the right size provided the outside
diameter _D_ is correct and the tool is of the correct form. As it would
be difficult to measure the width of this flat accurately, the thread
can be tested by screwing a standard nut over it if a standard thread is
being cut. If it is being fitted to a tapped hole, the tap itself is a
very convenient gage to use, the method being to caliper the tap and
then compare its size with the work.
[Illustration: Fig. 9. U. S. Standard Thread, Thread Tool, and Gage]
A good method of cutting a U. S. standard thread to a given size is as
follows: First turn the outside of the blank accurately to diameter _D_,
and then turn a small part of the end to diameter _r_ of the thread at
the root. The finishing cut for the thread is then taken with the tool
point set to just graze diameter _r_. If ordinary calipers were set to
diameter _r_ and measurements taken in the thread groove, the size would
be incorrect owing to the angularity of the groove, which makes it
necessary to hold the calipers at an angle when measuring. To determine
the root diameter divide 1.299 by the number of threads per inch and
subtract the quotient from the outside diameter. Expressing this rule as
a formula,
/1.299\
_r_ = _D_ - ( ----- )
\ _N_ /
in which _D_ equals outside diameter; _N_, the number of threads per
inch; and _r_, the root diameter. The number 1.299 is a constant that is
always used.
[Illustration: Fig. 10. End View of Lathe Headstock]
=Cutting a Left-hand Thread.=--The only difference between cutting
left-hand and right-hand threads in the lathe is in the movement of the
tool with relation to the work. When cutting a right-hand thread, the
tool moves from right to left, but this movement is reversed for
left-hand threads because the thread winds around in the opposite
direction. To make the carriage travel from left to right, the
lead-screw is rotated backwards by means of reversing gears _a_ and _b_
(Fig. 10) located in the headstock. Either of these gears can be
engaged with the spindle gear by changing the position of lever _R_.
When gear _a_ is in engagement, as shown, the drive from the spindle to
gear _c_ is through gears _a_ and _b_, but when lever _R_ is raised thus
shifting _b_ into mesh, the drive is direct and the direction of
rotation is reversed. The thread is cut by starting the tool at _a_,
Fig. 8, instead of at the end.
[Illustration: Fig. 11. End of Square Thread Tool, and Graphic Method of
Determining Helix Angle of Thread]
=Cutting a Square Thread.=--The form of tool used for cutting a square
thread is shown in Fig. 11. The width _w_ is made equal to one-half the
pitch of the thread to be cut and the end _E_ is at an angle with the
shank, which corresponds to the inclination _x--y_ of the threads. This
angle _A_ depends upon the diameter of the screw and the lead of the
thread; it can be determined graphically by drawing a line _a--b_ equal
in length to the circumference of the screw to be cut, and a line
_b--c_, at right angles, equal in length to the lead of the thread. The
angle [alpha] between lines _a--b_ and _a--c_ will be the required angle
_A_. (See end view of thread tool). It is not necessary to have this
angle accurate, ordinarily, as it is simply to prevent the tool from
binding against the sides of the thread. The end of a square thread tool
is shown in section to the right, to illustrate its position with
relation to the threads. The sides _e_ and _e_{1}_ are ground to slope
inward, as shown, to provide additional clearance.
When cutting multiple threads, which, owing to their increased lead,
incline considerably with the axis of the screw, the angles for each
side of the tool can be determined independently as follows: Draw line
_a--b_ equal in length to the circumference of the thread, as before, to
obtain the required angle _f_ of the rear or following side _e_{1}_; the
angle _l_ of the opposite or leading side is found by making _a--b_
equal to the circumference at the root of the thread. The tool
illustrated is for cutting right-hand threads; if it were intended for a
left-hand thread, the end, of course, would incline in the opposite
direction. The square thread is cut so that the depth _d_ is equal to
the width. When threading a nut for a square thread screw, it is the
usual practice to use a tool having a width slightly greater than
one-half the pitch, to provide clearance for the screw, and the width of
a tool for threading square-thread taps to be used for tapping nuts is
made slightly less than one-half the pitch.
=Cutting Multiple Threads.=--When a multiple thread is to be cut, such
as a double or triple thread, the lathe is geared with reference to the
number of single threads to the inch. For example, the lead of the
double thread, shown at _B_, Fig. 12, is one-half inch, or twice the
pitch, and the number of single threads to the inch equals 1 ÷ 1/2 = 2.
Therefore, the lathe is geared for cutting two threads per inch. The
first cut is taken just as though a single thread were being cut,
leaving the work as shown at _A_. When this cut is finished the work is
turned one-half a revolution (for a double thread) without disturbing
the position of the lead-screw or carriage, which brings the tool midway
between the grooves of the single thread as indicated by dotted lines.
The second groove is then cut, producing a double thread as shown at
_B_. In the case of a triple thread, the work would be indexed one-third
of a revolution after turning the first groove, and then another third
revolution to locate the tool for cutting the last groove. Similarly,
for a quadruple thread, it would be turned one-quarter revolution after
cutting each successive groove or thread.
There are different methods of indexing the work when cutting multiple
threads, in order to locate the tool in the proper position for cutting
another thread groove. Some machinists, when cutting a double thread,
simply remove the work from the lathe and turn it one-half a revolution
by placing the tail of the driving dog in the opposite slot of the
faceplate. This is a very simple method, but if the slots are not
directly opposite or 180 degrees apart, the last thread will not be
central with the first. Another and better method is to disengage the
idler gear from the gear on the stud, turn the spindle and work
one-half, or one-third, of a revolution, as the case might be, and then
connect the gears. For example, if the stud gear had 96 teeth, the tooth
meshing with the idler gear would be marked with chalk, the gears
disengaged, and the spindle turned until the chalked tooth had made the
required part of a revolution, which could be determined by counting the
teeth. When this method is used, the number of teeth in the stud gear
must be evenly divisible by two if a double thread is being cut, or by
three for a triple thread, etc. If the stud is not geared to the spindle
so that each makes the same number of revolutions, the ratio of the
gearing must be considered.
[Illustration: Fig. 12. Views illustrating how a Double Square Thread is
Cut]
=Setting Tool When Cutting Multiple Threads.=--Another method, which can
sometimes be used for setting the tool after cutting the first groove of
a multiple thread, is to disengage the lock-nuts from the lead-screw
(while the spindle is stationary) and move the carriage back whatever
distance is required to locate the tool in the proper position for
taking the second cut. Evidently this distance must not only locate the
tool in the right place, but be such that the lock-nuts can be
re-engaged with the lead-screw. Beginning with a simple illustration,
suppose a double thread is being cut having a lead of 1 inch. After the
first thread groove is cut, the tool can be set in a central position
for taking the second cut, by simply moving the carriage back 1/2 inch
(one-half the lead), or 1/2 inch plus the lead or any multiple of the
lead. If the length of the threaded part were 5 inches, the tool would
be moved back far enough to clear the end of the work, or say 1/2 + 5 =
5-1/2 inches. In order to disengage the lock-nuts and re-engage them
after moving the carriage 5-1/2 inches (or any distance equal, in this
case, to one-half plus a whole number), the lead-screw must have an even
number of threads per inch.
Assume that a double thread is being cut having 1-1/4 single threads per
inch. The lead then would equal 1 ÷ 1-1/4 = 0.8 inch, and if the
carriage is moved back 0.8 ÷ 2 = 0.4 inch, the tool will be properly
located for the second cut; but the lock-nuts could not be re-engaged
unless the lead-screw had ten threads per inch, which is finer than the
pitch found on the lead-screws of ordinary engine lathes. However, if
the movement were 0.4 + 0.8 × 2 = 2 inches, the lock-nuts could be
re-engaged regardless of the number of threads per inch on the
lead-screw. The rule then, is as follows:
_Divide the lead of the thread by 2 for a double thread, 3 for a triple
thread, 4 for a quadruple thread, etc., thus obtaining the pitch; then
add the pitch to any multiple of the lead, which will give a movement,
in inches, that will enable the lock-nuts to be re-engaged with the
lead-screw._
Whenever the number obtained by this rule is a whole number, obviously,
the movement can be obtained with a lead-screw of any pitch. If the
number is fractional, the number of threads per inch on the lead-screw
must be divisible by the denominator of the fraction.
To illustrate the application of the foregoing rule, suppose a quadruple
thread is to be cut having 1-1/2 single threads per inch (which would be
the number the lathe would be geared to cut). Then the lead of the
thread = 1 ÷ 1-1/2 = 0.6666 inch and the pitch = 0.6666 ÷ 4 = 0.1666
inch; adding the pitch to twice the lead we have 0.1666 + 2 × 0.6666 =
1.499 inch. Hence, if the carriage is moved 1-1/2 inch (which will
require a lead-screw having an even number of threads per inch), the
tool will be located accurately enough for practical purposes. When the
tool is set in this way, if it does not clear the end of the part being
threaded, the lathe can be turned backward to place the tool in the
proper position.
[Illustration: Fig. 13. Indexing Faceplate used for Multiple Thread
Cutting]
The foregoing rule, as applied to triple threads or those of a higher
number, does not always give the only distance that the carriage can be
moved. To illustrate, in the preceding example the carriage movement
could be equal to 0.499, or what is practically one-half inch, instead
of 1-1/2 inch, and the tool would be properly located. The rule,
however, has the merit of simplicity and can be used in most cases.
Special faceplates are sometimes used for multiple thread cutting, that
enable work to be easily and accurately indexed. One of these is
illustrated in Fig. 13; it consists of two parts _A_ and _B_, part _A_
being free to rotate in relation to _B_ when bolts _C_ are loosened. The
driving pin for the lathe dog is attached to plate _A_. When one groove
of a multiple thread is finished, bolts _C_ are loosened and plate _A_
is turned around an amount corresponding to the type of thread being
cut. The periphery of plate _A_ is graduated in degrees, as shown, and
for a double thread it would be turned one-half revolution or 180
degrees, for a triple thread, 120 degrees, etc. This is a very good
arrangement where multiple thread cutting is done frequently.
[Illustration: Fig. 14. Correct and Incorrect Positions of Tool for
Taper Thread Cutting]
=Taper Threading.=--When a taper thread is to be cut, the tool should be
set square with axis _a--a_ as at _A_, Fig. 14, and not by the tapering
surface as at _B_. If there is a cylindrical part, the tool can be set
as indicated by the dotted lines. All taper threads should be cut by the
use of taper attachments. If the tailstock is set over to get the
required taper, and an ordinary bent-tail dog is used for driving, the
curve of the thread will not be true, or in other words the thread will
not advance at a uniform rate; this is referred to by machinists as a
"drunken thread." This error in the thread is due to the angularity
between the driving dog and the faceplate, which causes the work to be
rotated at a varying velocity. The pitch of a taper thread that is cut
with the tailstock set over will also be slightly finer than the pitch
for which the lathe is geared. The amount of these errors depends upon
the angle of the taper and the distance that the center must be offset.
=Internal Threading.=--Internal threading, or cutting threads in holes,
is an operation performed on work held in the chuck or on a faceplate,
as for boring. The tool used is similar to a boring tool except that the
working end is shaped to conform to the thread to be cut. The method of
procedure, when cutting an internal thread, is similar to that for
outside work, as far as handling the lathe is concerned. The hole to be
threaded is first bored to the root diameter _D_, Fig. 15, of the screw
that is to fit into it. The tool-point (of a tool for a U. S. standard
or V-thread) is then set square by holding a gage _G_ against the true
side of the work and adjusting the point to fit the notch in the gage as
shown. The view to the right shows the tool taking the first cut.
[Illustration: Fig. 15. Method of setting and using Inside Thread Tool]
Very often the size of a threaded hole can be tested by using as a gage
the threaded part that is to fit into it. When making such a test, the
tool is, of course, moved back out of the way. It is rather difficult to
cut an accurate thread in a small hole, especially when the hole is
quite deep, owing to the flexibility of the tool; for this reason
threads are sometimes cut slightly under size with the tool, after which
a tap with its shank end held straight by the tailstock center is run
through the hole. In such a case, the tap should be calipered and the
thread made just small enough with the tool to give the tap a light cut.
Small square-threaded holes are often finished in this way, and if a
number of pieces are to be threaded, the use of a tap makes the holes
uniform in size.
=Stop for Thread Tools.=--When cutting a thread, it is rather difficult
to feed in the tool just the right amount for each successive cut,
because the tool is moved in before it feeds up to the work. A stop is
sometimes used for threading which overcomes this difficulty. This stop
consists of a screw _S_, Fig. 16, which enters the tool slide and passes
through a block _B_ clamped in front of the slide. The hole in the block
through which the stop-screw passes is not threaded, but is large enough
to permit the screw to move freely. When cutting a thread, the tool is
set for the first cut and the screw is adjusted until the head is
against the fixed block. After taking the first cut, the stop-screw is
backed out, say one-half revolution, which allows the tool to be fed in
far enough for a second cut. If this cut is about right for depth, the
screw is again turned about one-half revolution for the next cut and
this is continued for each successive cut until the thread is finished.
By using a stop of this kind, there is no danger of feeding the tool in
too far as is often done when the tool is set by guess. If this form of
stop is used for internal threading, the screw, instead of passing
through the fixed block, is placed in the slide so that the end or head
will come against the stop _B_. This change is made because the tool is
fed outward when cutting an internal thread.
[Illustration: Fig. 16. Cross-slide equipped with Stop for Regulating
Depth of Cut when Threading]
=The Acme Standard Thread.=--The Acme thread is often used, at the
present time, in place of a square thread. The angle between the sides
of the Acme thread is 29 degrees (see Fig. 21) and the depth is made
equal to one-half the pitch plus 0.010 inch to provide clearance and
insure a bearing upon the sides. The thread tool is ordinarily ground to
fit a gage having notches representing different pitches. An improved
form of Acme thread gage is shown in Fig. 17. The tool point is first
ground to the correct angle by fitting it to the 29-degree notch in the
end of the gage, as at _A_. The end is then ground to the proper width
for the pitch to be cut, by testing it, as at _B_. The numbers opposite
the shallow notches for gaging the width represent the number of threads
per inch. With this particular gage, the tool can be set square by
placing edge _D_ against the turned surface to be threaded, and
adjusting the tool until the end is in line with the gage, as at _C_. By
placing the tool in this position, the angle between the side and the
end can also be tested.
[Illustration: Fig. 17. Gage for grinding and setting Acme Thread Tools]
In case it should be necessary to measure the end width of an Acme
thread tool, for a pitch not on the regular gage, this can be done by
using a vernier gear-tooth caliper, as indicated in Fig. 18. If we
assume that the caliper jaws bear on the sides of the tool at a distance
_A_ from the top, equal to 1/4 inch, then the width of the tool point
equals the caliper reading (as shown by the horizontal scale) minus
0.1293 inch. For example, if the caliper reading was 0.315 inch, the
width at the point would equal 0.315 - 0.1293 = 0.1857 inch, assuming that
the sides were ground to the standard angle of 29 degrees. The constant
to be subtracted from the caliper reading equals 2 _A_ tan 14° 30' or,
in this case, 2 × 0.25 × 0.2586 = 0.1293.
[Illustration: Fig. 18. Measuring Width of Acme Thread Tool with Vernier
Gear-tooth Caliper]
=The Whitworth Thread.=--The Whitworth (or British Standard Whitworth)
thread, which is used principally in Great Britain, has an included
angle of 55 degrees, and the threads are rounded at the top and at the
root, as shown in Fig. 23. The shape of the tool used for cutting this
thread is also shown in this illustration. The end is rounded to form
the fillet at the root of the thread, and the round corners on the sides
give the top of the thread the required curvature. Every pitch requires
a different tool, and the cutting end is given the curved form by
milling or hobbing. The hob used for this purpose is accurately threaded
to correspond with the pitch for which the tool is required, and then it
is fluted to form cutting edges, and is hardened. The hob is then used
like a milling cutter for forming the end of the thread tool. The tool
is sharpened by grinding on the top. The method of cutting a Whitworth
thread is, of course, similar to that followed for a U. S. standard or
V-thread, in that the tool is set square with the unthreaded blank and
at the same height as the lathe centers, in order to secure a thread of
the proper form. Care should be taken to turn the blank to the right
diameter so that the top of the thread will be fully rounded when the
screw is the required size.
[Illustration: Fig. 19. United States Standard Thread]
[Illustration: Fig. 20. Standard Sharp V-thread]
[Illustration: Fig. 21. Acme Standard Thread]
[Illustration: Fig. 22. Square Thread]
[Illustration: Fig. 23. Whitworth Standard Thread]
[Illustration: Fig. 24. Standard Worm Thread]
=Worm Threads.=--The standard worm thread has an angle of 29 degrees
between the sides, the same as an Acme thread, but the depth of a worm
thread and the width of the flat at the top and bottom differ from the
Acme standard, as will be seen by comparing Figs. 21 and 24. The whole
depth of the thread equals the linear pitch multiplied by 0.6866, and
the width of the thread tool at the end equals the linear pitch
multiplied by 0.31. Gages notched for threads of different pitch are
ordinarily used when grinding worm thread tools.
When it is necessary to cut multiple-threaded worms of large lead in an
ordinary lathe, difficulty is sometimes experienced because the
lead-screw must be geared to run much faster than the spindle, thus
imposing excessive strains on the gearing. This difficulty is sometimes
overcome by mounting a belt pulley on the lead-screw, beside the change
gear, and connecting it to the countershaft by a belt; the spindle is
then driven through the change gearing from the lead-screw, instead of
_vice versa_.
=Coarse Threading Attachment.=--To avoid the difficulties connected with
cutting threads of large lead, some lathes are equipped with a coarse
screw-cutting attachment. The arrangement of this attachment, as made by
the Bradford Machine Tool Co., is as follows: On the usual reversing
shaft, and inside of the headstock, there is a sliding double gear, so
arranged as to be engaged with either the usual gear on the spindle, or
with a small pinion at the end of the cone. The gears are so
proportioned that the ratio of the two engagements is as 10 to 1; that
is, when engaged with the cone gear (the back-gears being thrown in) the
mating gear will make ten revolutions to one of the spindle, so that
when the lathe is ordinarily geared to cut one thread per inch, it will,
when driven by the cone pinion, cut one thread in ten inches. This
construction dispenses with the extra strain on the reverse gears due to
moving the carriage at the rapid rate that would be necessary for such a
large lead, when not using an attachment. These attachments are not only
extensively used for the cutting of coarse screws but for cutting oil
grooves on cylindrical parts.
When cutting a thread of large lead or "steep pitch," the top of the
thread tool should be ground so that it is at right angles to the
thread; then the thread groove will be cut to the same width as the
tool.
=Testing the Size of a Thread.=--When the thread tool has been fed in
far enough to form a complete thread, the screw is then tested for size.
If we assume that a bolt is being threaded for a standard nut, it would
be removed from the lathe and the test made by screwing a nut on the
end. If the thread were too large, the nut might screw on very tightly
or not at all; in either case, the work would again be placed in the
lathe and a light cut taken over it to reduce the thread to the proper
size. When replacing a threaded part between the centers, it should be
put back in the original position, that is, with the "tail" of the
driving dog in the same slot of the faceplate it previously occupied.
[Illustration: Fig. 25. Testing Diameter of Thread with Calipers and
Micrometer]
As it is difficult to tell just when a thread is cut to the exact size,
special thread calipers having wedge-shaped ends are sometimes used for
measuring the diameter of a V-thread or a U. S. standard thread, at the
bottom of the grooves or the root diameter, as shown at _A_ in Fig. 25.
These calipers can be set from a tap corresponding to the size of the
thread being cut, or from a previously threaded piece of the right
size.
=The Thread Micrometer.=--Another form of caliper for testing threads is
shown at _B_. This is one of the micrometer type and is intended for
very accurate work. The spindle of this micrometer has a conical end and
the "anvil" is V-shaped, and these ends bear on the sides of the thread
or the surfaces which form the bearing when the screw is inserted in a
nut or threaded hole. The cone-shaped point is slightly rounded so that
it will not bear in the bottom of the thread. There is also sufficient
clearance at the bottom of the V-shaped anvil to prevent it from bearing
on top of the thread. The diameter as indicated by this micrometer is
the "pitch diameter" of the thread and is equal to the outside diameter
minus the depth of one thread. This depth may be determined as follows:
Depth of a V-thread = 0.866 ÷ No. of threads per inch;
Depth of a U. S. standard thread = 0.6495 ÷ No. of threads per inch;
Depth of Whitworth thread = 0.6403 ÷ No. of threads per inch.
The movable point measures all pitches, but the fixed anvil is limited
in its capacity, for if made large enough to measure a thread of, say,
1/4-inch pitch, it would be too wide at the top to measure a thread of
1/24-inch pitch, hence each caliper is limited in the range of threads
that the anvil can measure. When measuring the "angle diameter" of a
thread, the micrometer should be passed back and forth across the
thread, in order to make sure that the largest dimension or the actual
diameter is being measured. If the micrometer is placed over what seems
to be the center of the screw and the reading is taken by simply
adjusting in the anvil or point against the thread, without moving the
micrometer back and forth across it, an incorrect reading may be
obtained.
If standard threaded reference gages are available, the size of the
thread being cut can be tested by comparing it with the gage.
Micrometers having small spherical measuring ends (see sketch _A_, Fig.
26) are sometimes used for this purpose. The ball points are small
enough to bear against the sides of the thread and the diameter, as
compared with the reference gage, can be determined with great
accuracy.
[Illustration: Fig. 26. (A) Testing Size of Thread with Ball-point
Micrometer. (B) Testing Size of V-thread by the Three-wire System. (C)
Testing the Size of a U. S. Standard Thread]
=Three-wire System of Measuring Threads.=--A method of measuring threads
by using an ordinary micrometer and three wires of equal diameter is
illustrated at _B_ and _C_, Fig. 26. Two wires are placed between the
threads on one side and one on the opposite side of the screw. The
dimension _M_ over the wires is then measured with an ordinary
micrometer. When the thread is cut to a standard size, the dimension _M_
for different threads is as follows:
For a U. S. standard thread:
_m_ = _d_ - 1.5155_p_ + 3_w_
For a sharp V-thread:
_m_ = _d_ - 1.732_p_ + 3_w_
For a Whitworth standard thread:
_m_ = _d_ - 1.6008_p_ + 3.1657_w_
In these formulas, _d_ = standard outside diameter of screw; _m_ =
measurement over wires; _w_ = diameter of wires; _p_ = pitch of thread =
1 ÷ number of threads per inch.
To illustrate the use of the formula for the U. S. standard thread, let
us assume that a screw having 6 threads per inch (1/6-inch pitch) is to
be cut to a diameter of 1-1/2 inch, and that wires 0.140 inch diameter
are to be used in conjunction with a micrometer for measurement. Then
the micrometer reading _m_ should be
1-1/2 - 1.5155 × 1/6 + 3 × 0.140 = 1.6674 inch
If the micrometer reading were 1.670 inch, it would indicate that the
pitch diameter of the screw was too large, the error being equal to
difference between 1.667 and the actual reading.
[Illustration: Fig. 27. Rivett-Dock Circular Threading Tool in Working
Position]
=Rivett-Dock Threading Tool.=--A special form of thread tool, which
overcomes a number of disadvantages common to an ordinary single-point
thread tool, is shown in Fig. 27. This tool has a circular-shaped cutter
_C_, having ten teeth around its circumference, which, beginning with
tooth No. 1, gradually increase in height, cutter No. 2 being higher
than No. 1, etc. This cutter is mounted on a slide _S_, that is fitted
to the frame _F_, and can be moved in or out by lever _L_. The hub of
this lever has an eccentric stud which moves slide _S_ and locks it when
in the forward or cutting position. The action of the lever in moving
the slide engages the cutter with pawl _P_, thus rotating the cutter one
tooth at a time and presenting a different tooth to the work for each
movement of the lever. When the slide is moved forward, the heel or
underside of the tooth which is in the working position rests on a stop
that takes the thrust of the cut.
When the tool is in use, it is mounted on the tool-block of the lathe as
shown in the illustration. The cutter is set for height by placing a
tooth in the working position and setting the top level with the lathe
center. The cutter is also set square with the work by using an ordinary
square, and it is tilted slightly from the vertical to correspond with
the angle of the thread to be cut, by adjusting frame _F_. At first a
light cut is taken with lever _L_ moved forward and tooth No. 1 on the
stop. After this cut is completed, the lever is reversed which rotates
the cutter one tooth, and the return movement places tooth No. 2 in the
working position. This operation is repeated until the tenth tooth
finishes the thread. It is often necessary, when using a single-point
thread tool, to re-sharpen it before taking the finishing cut, but with
a circular tool this is not necessary, for by using the different teeth
successively, the last tooth, which only takes finishing cuts, is kept
in good condition.
=Cutting Screws to Compensate for Shrinkage.=--Some tool steels are
liable to shrink more or less when they are hardened; consequently if a
very accurate hardened screw is required, it is sometimes cut so that
the pitch is slightly greater than standard, to compensate for the
shrinkage due to the hardening operation. As the amount of contraction
incident to hardening is very little, it is not practicable to use
change gears that will give the exact pitch required. A well-known
method of obtaining this increase of pitch is by the use of a taper
attachment.
For example, suppose a tap having 8 threads per inch is to be threaded,
and, owing to the contraction of the steel, the pitch must be 0.12502
inch instead of 0.125 inch. The lathe is geared to cut 8 threads per
inch or 0.125 inch pitch, and then the taper attachment is set to an
angle _a_, Fig. 28, the cosine of which equals 0.125/0.12502; that is,
the cosine of angle _a_ equals _the pitch required after hardening_,
divided by the _pitch necessary to compensate for shrinkage_. The angle
is then found by referring to a table of cosines. The tap blank is also
set to the same angle a by adjusting the tailstock center, thus locating
the axis of the work parallel with the slide of the taper attachment.
When the carriage moves a distance _x_, the tool point will have moved a
greater distance _y_ along the work, the difference between x and y
depending upon angle _a_; hence the tool will cut a thread of slightly
greater pitch than the lathe is geared to cut.
To illustrate by using the preceding example, cosine of angle _a_ =
0.125/0.12502 = 0.99984. By referring to a table of cosines, we find
that 0.99984 is the cosine of 1 degree, approximately; hence, the taper
attachment slide and the work should be set to this angle. (The angle
_a_ in Fig. 28 has been exaggerated in order to more clearly illustrate
the principle.)
[Illustration: Fig. 28. Diagram Illustrating Method of Cutting a Thread
to Compensate for the Error in Pitch due to Shrinkage in Hardening]
As is well known, it is objectionable to cut a thread with the tailstock
center offset, because the work is not rotated at a uniform velocity,
owing to the fact that the driving dog is at an angle with the
faceplate. For a small angle such as 1 degree, however, the error
resulting from this cause would be very small.
If a thread having a pitch slightly less than standard is needed to fit
a threaded part which has contracted in hardening, the taper attachment
can also be used provided the lathe is equipped with special gears to
cut a little less than the required pitch. Suppose a screw having a
pitch of 0.198 inch is required to fit the thread of a nut the pitch of
which has been reduced from 0.200 inch to 0.198 inch. If gears having 83
and 84 teeth are available, these can be inserted in a compound train,
so as to reduce the 0.200 inch pitch that would be obtained with the
regular gearing, to 83/84 of 0.200 or 0.19762 inch. This pitch, which is
less than the 0.198 inch pitch required, is then increased by using the
taper attachment as previously described. (This method was described by
Mr. G. H. Gardner in MACHINERY, February, 1914.)
=Calculating Change Gears for Thread Cutting.=--As previously mentioned,
the change gears for cutting threads of various pitches are shown by a
table or "index plate" attached to the lathe. The proper gears to be
used can be calculated, but the use of the table saves time and tends to
avoid mistakes. Every machinist, however, should know how to determine
the size of gears used for cutting any number of threads to the inch.
Before referring to any rules, let us first consider why a lathe cuts a
certain number of threads to the inch and how this number is changed by
the use of different gears.
As the carriage _C_ and the tool are moved by the lead-screw _S_ (see
Fig. 2), which is geared to the spindle, the number of threads to the
inch that are cut depends, in every case, upon the number of turns the
work makes while the lead-screw is moving the carriage one inch. If the
lead-screw has six threads per inch, it will make six revolutions while
the carriage and the thread tool travel one inch along the piece to be
threaded. Now if the change gears _a_ and _c_ (see also sketch _A_, Fig.
29) are so proportioned that the spindle makes the same number of
revolutions as the lead-screw, in a given time, it is evident that the
tool will cut six threads per inch. If the spindle revolved twice as
fast as the lead-screw, it would make twelve turns while the tool moved
one inch, and, consequently, twelve threads per inch would be cut; but
to get this difference in speeds it is necessary to use a combination of
gearing that will cause the lead-screw to revolve once while the lathe
spindle and work make two revolutions.
[Illustration: Fig. 29. (A) Lathe with Simple Gearing for Thread
Cutting. (B) Compound Geared Lathe]
Suppose that nine threads to the inch are to be cut and the lead-screw
has six threads per inch. In this case the work must make nine
revolutions while the lead-screw makes six and causes the carriage and
thread tool to move one inch, or in other words, one revolution of the
lead-screw corresponds to one and one-half revolution of the spindle;
therefore, if the lead-screw gear _c_ has 36 teeth, the gear _a_ on the
spindle stud should have 24 teeth. The spindle will then revolve one and
one-half times faster than the lead-screw, provided the stud rotates at
the same rate of speed as the main lathe spindle. The number of teeth in
the change gears that is required for a certain pitch can be found by
multiplying the number of threads per inch of the lead-screw, and the
number of threads per inch to be cut, by the same trial multiplier. The
formula which expresses the relation between threads per inch of
lead-screw, threads per inch to be cut, and the number of teeth in the
change gears, is as follows:
threads per inch of lead-screw teeth in gear on spindle stud
------------------------------ = -----------------------------
threads per inch to be cut teeth in gear on lead-screw
Applying this to the example given, we have 6/9 = 24/36. The values of
36 and 24 are obtained by multiplying 6 and 9, respectively, by 4,
which, of course, does not change the proportion. Any other number could
be used as a multiplier, and if gears having 24 and 36 teeth were not
available, this might be necessary. For example, if there were no gears
of this size, some other multiplier as 5 or 6 might be used.
Suppose the number of teeth in the change gears supplied with the lathe
are 24, 28, 32, 36, etc., increasing by four teeth up to 100, and assume
that the lead-screw has 6 threads per inch and that 10 threads per inch
are to be cut. Then,
6 6 × 4 24
-- = ------ = --
10 10 × 4 40
By multiplying both numerator and denominator by 4, we obtain two
available gears having 24 and 40 teeth, respectively. The 24-tooth gear
goes on the spindle stud and, the 40-tooth gear on the lead-screw. The
number of teeth in the intermediate or "idler" gear _b_, which connects
the stud and lead-screw gears, is not considered as it does not affect
the ratios between gears _a_ and _c_, but is used simply to transmit
motion from one gear to the other.
We have assumed in the foregoing that the spindle stud (on which gear
_a_ is mounted) and the main spindle of the lathe are geared in the
ratio of one to one and make the same number of revolutions. In some
lathes, however, these two members do not rotate at the same speed, so
that if equal gears were placed on the lead-screw and spindle stud, the
spindle would not make the same number of revolutions as the lead-screw.
In that case if the actual number of threads per inch in the lead-screw
were used when calculating the change gears, the result would be
incorrect; hence, to avoid mistakes, the following general rule should
be used as it gives the correct result, regardless of the ratios of the
gears which connect the spindle and spindle stud:
_Rule.--First find the number of threads per inch that is cut when gears
of the same size are placed on the lead-screw and spindle, either by
actual trial or by referring to the index plate. Then place this number
as the numerator of a fraction and the number of threads per inch to be
cut, as the denominator; multiply both numerator and denominator by some
trial number, until numbers are obtained which correspond to numbers of
teeth in gears that are available._ The product of the trial number and
the numerator (or "lathe screw constant") represents the gear _a_ for
the spindle stud, and the product of the trial number and the
denominator, the gear for the lead-screw.
=Lathes with Compound Gearing.=--When gearing is arranged as shown at
_A_, Fig. 29, it is referred to as simple gearing, but sometimes it is
necessary to introduce two gears between the stud and screw as at _B_,
which is termed compound gearing. The method of figuring compound
gearing is practically the same as that for simple gearing. To find the
change gears used in compound gearing, place the "screw constant"
obtained by the foregoing rule, as the numerator, and the number of
threads per inch to be cut as the denominator of a fraction; resolve
both numerator and denominator into two factors each, and multiply each
"pair" of factors by the same number, until values are obtained
representing numbers of teeth in available change gears. (One factor in
the numerator and one in the denominator make a "pair" of factors.)
Suppose the lathe cuts 6 threads per inch when gears of equal size are
used, and that the number of teeth in the gears available are 30, 35, 40
and so on, increasing by 5 up to 100. If 24 threads per inch are to be
cut, the screw constant 6 is placed in the numerator and 24 in the
denominator. The numerator and denominator are then divided into factors
and each pair of factors is multiplied by the same number to find the
gears, thus:
6 2 × 3 (2 × 20) × (3 × 10) 40 × 30
-- = ----- = ------------------- = -------
24 4 × 6 (4 × 20) × (6 × 10) 80 × 60
The last four numbers indicate the gears which should be used. The upper
two having 40 and 30 teeth are the _driving_ gears and the lower two
having 80 and 60 teeth are the _driven_ gears. The driving gears are
gear _a_ on the spindle stud and gear _c_ on the intermediate stud,
meshing with the lead-screw gear, and the driven gears are gears _b_ and
_d_. It makes no difference which of the driving gears is placed on the
spindle stud, or which of the driven is placed on the lead-screw.
=Fractional Threads.=--Sometimes the lead of a thread is given as a
fraction of an inch instead of stating the number of threads per inch.
For example, a thread may be required to be cut, having 3/8-inch lead.
The expression "3/8-inch lead" should first be transformed to "number of
threads per inch." The number of threads per inch (the thread being
single) equals:
1 3 8
--- = 1 ÷ - = - = 2-2/3
3/8 8 3
To find the change gears to cut 2-2/3 threads per inch in a lathe having
a screw constant of 8 and change gears varying from 24 to 100 teeth,
increasing by 4, proceed as follows:
8 2 × 4 (2 × 36) × (4 × 24) 72 × 96
----- = --------- = ----------------------- = -------
2-2/3 1 × 2-2/3 (1 × 36) × (2-2/3 × 24) 36 × 64
As another illustration, suppose we are to cut 1-3/4 thread per inch on
a lathe having a screw constant of 8, and that the gears have 24, 28,
32, 36, 40 teeth, etc., increasing by four up to one hundred. Following
the rule:
8 2 × 4 (2 × 36) × (4 × 16) 72 × 64
----- = --------- = ----------------------- = -------
1-3/4 1 × 1-3/4 (1 × 36) × (1-3/4 × 16) 36 × 28
The gears having 72 and 64 teeth are the _driving_ gears, and those with
36 and 28 teeth are the _driven_ gears.
=Change Gears for Metric Pitches.=--When screws are cut in accordance
with the metric system, it is the usual practice to give the lead of the
thread in millimeters, instead of the number of threads per unit of
measurement. To find the change gears for cutting metric threads, when
using a lathe having an English lead-screw, first determine the number
of threads per inch corresponding to the given lead in millimeters.
Suppose a thread of 3 millimeters lead is to be cut in a lathe having an
English lead-screw and a screw constant of 6. As there are 25.4
millimeters per inch, the number of threads per inch will equal 25.4 ÷
3. Place the screw constant as the numerator, and the number of threads
per inch to be cut as the denominator:
6 25.4 6 × 3
------- = 6 ÷ ---- = -----
25.4 3 25.4
----
3
The numerator and denominator of this fractional expression of the
change-gear ratio are next multiplied by some trial number to determine
the size of the gears. The first whole number by which 25.4 can be
multiplied so as to get a whole number as the result is 5. Thus, 25.4 ×
5 = 127; hence, one gear having 127 teeth is always used when cutting
metric threads with an English lead-screw. The other gear required in
this case has 90 teeth. Thus:
6 × 3 × 5 90
--------- = ---
25.4 × 5 127
Therefore, the following rule can be used to find the change gears for
cutting metric pitches with an English lead-screw:
_Rule.--Place the lathe screw constant multiplied by the lead of the
required thread in millimeters multiplied by 5, as the numerator of the
fraction, and 127 as the denominator. The product of the numbers in the
numerator equals the number of teeth for the spindle-stud gear, and 127
is the number of teeth for the lead-screw gear._
If the lathe has a metric pitch lead-screw, and a screw having a given
number of threads per inch is to be cut, first find the "metric screw
constant" of the lathe or the lead of thread in millimeters that would
be cut with change gears of equal size on the lead-screw and spindle
stud; then the method of determining the change gears is simply the
reverse of the one already explained for cutting a metric thread with an
English lead-screw.
_Rule.--To find the change gears for cutting English threads with a
metric lead-screw, place 127 in the numerator and the threads per inch
to be cut, multiplied by the metric screw constant multiplied by 5, in
the denominator; 127 is the number of teeth on the spindle-stud gear and
the product of the numbers in the denominator equals the number of teeth
in the lead-screw gear._
=Quick Change-gear Type of Lathe.=--A type of lathe that is much used at
the present time is shown in Fig. 30. This is known as the quick
change-gear type, because it has a system of gearing which makes it
unnecessary to remove the change gears and replace them with different
sizes for cutting threads of various pitches. Changes of feed are also
obtained by the same mechanism, but the feeding movement is transmitted
to the carriage by the rod _R_, whereas the screw _S_{1}_ is used for
screw cutting. As previously explained, the idea of using the screw
exclusively for threading is to prevent it from being worn excessively,
as it would be if continually used in place of rod _R_, for feeding the
carriage when turning.
[Illustration: Fig. 30. Lathe having Quick Change-gear Mechanism]
[Illustration: Fig. 31. End and Side Views of Quick Change-gear
Mechanism]
The general construction of this quick change gear mechanism and the
way the changes are made for cutting threads of different pitch, will be
explained in connection with Figs. 30, 31 and 32, which are marked with
the same reference letters for corresponding parts. Referring to Fig.
30, the movement is transmitted from gear _s_ on the spindle stud
through idler gear _I_, which can be moved sidewise to mesh with either
of the three gears _a_, _b_ or _c_, Fig. 31. This cone of three gears
engages gears _d_, _e_ and _f_, any one of which can be locked with
shaft _T_ (Fig. 32) by changing the position of knob _K_. On shaft _T_
there is a gear _S_ which can be moved along the shaft by hand lever _L_
and, owing to the spline or key _t_, both the sliding gear and shaft
rotate together. Shaft _T_, carrying gears _d_, _e_ and _f_ and the
sliding gear _S_, is mounted in a yoke _Y_, which can be turned about
shaft _N_, thus making it possible to lower sliding gear _S_ into mesh
with any one of a cone of eight gears _C_, Fig. 31. The shaft on which
the eight gears are mounted has at the end a small gear _m_ meshing with
gear _n_ on the feed-rod, and the latter, in turn, drives the
lead-screw, unless gear _o_ is shifted to the right out of engagement,
which is its position except when cutting threads.
[Illustration: Fig. 32. Sectional Views of Quick Change-gear Mechanism]
With this mechanism, eight changes for different threads or feeds are
obtained by simply placing gear _S_ into mesh with the various sized
gears in cone _C_. As the speed of shaft _T_ depends on which of the
three gears _d_, _e_ and _f_ are locked to it, the eight changes are
tripled by changing the position of knob _K_, making twenty-four. Now by
shifting idler gear _I_, three speed changes may be obtained for gears
_a_, _b_ and _c_, which rotate together, so that the twenty-four changes
are also tripled, giving a total of seventy-two variations without
removing any gears, and if a different sized gear _s_ were placed on the
spindle stud, an entirely different range could be obtained, but such a
change would rarely be necessary. As shown in Fig. 30, there are eight
hardened steel buttons _B_, or one for each gear of the cone _C_, placed
at different heights in the casing. When lever _L_ is shifted sidewise
to change the position of sliding gear _S_, it is lowered onto one of
these buttons (which enters a pocket on the under side) and in this way
gear _S_ is brought into proper mesh with any gear of the cone _C_. To
shift lever _L_, the handle is pulled outward against the tension of
spring _r_ (Fig. 32), which disengages latch _l_ and enables the lever
to be lifted clear of the button; yoke _Y_ is then raised or lowered, as
the case may be, and lever _L_ with the sliding gear is shifted
laterally to the required position.
[Illustration: Fig. 33. Index Plate showing Position of Control Levers
for Cutting Threads of Different Pitch]
The position of lever _L_ and knob _K_ for cutting threads of different
pitches is shown by an index plate or table attached to the lathe and
arranged as shown in Fig. 33. The upper section _a_ of this table shows
the different numbers of threads to the inch that can be obtained when
idler gear _I_ is in the position shown by the diagram _A_. Section _b_
gives the changes when the idler gear is moved, as shown at _B_, and,
similarly, section _c_ gives the changes for position _C_ of the idler.
The horizontal row of figures from 1 to 8 below the word "stops"
represents the eight positions for lever _L_, which has a plate _p_
(Fig. 30) just beneath it with corresponding numbers, and the column to
the left shows whether knob _K_ should be out, in a central position, or
in.
In order to find what the position of lever _L_ and knob _K_ should be
for cutting any given number of threads to the inch, find what "stop"
number is directly above the number of threads to be cut, which will
indicate the location of lever _L_, and also what position should be
occupied by knob _K_, as shown in the column to the left. For example,
suppose the lathe is to be geared for cutting eight threads to the inch.
By referring to section a we see that lever _L_ should be in position 4
and knob _K_ in the center, provided the idler gear _I_ were in position
_A_, as it would be ordinarily, because all standard numbers of threads
per inch (U. S. standard) from 1/4 inch up to and including 4 inches in
diameter can be cut with the idler gear in that position. As another
illustration, suppose we want to cut twenty-eight threads per inch. This
is listed in section _c_, which shows that lever _L_ must be placed in
position 3 with knob _K_ pushed in and the idler gear shifted to the
left as at _C_.
The simplicity of this method as compared with the time-consuming
operation of removing and changing gears is apparent. The diagram _D_ to
the right shows an arrangement of gearing for cutting nineteen threads
per inch. A 20-tooth gear is placed on the spindle stud (in place of the
regular one having 16 teeth) and one with 95 teeth on the lead-screw,
thus driving the latter direct as with ordinary change gears. Of course
it will be understood that the arrangement of a quick change-gear
mechanism varies somewhat on lathes of different make.
CHAPTER V
TURRET LATHE PRACTICE
Turret lathes are adapted for turning duplicate parts in quantity. The
characteristic feature of a turret lathe is the turret which is mounted
upon a carriage and contains the tools which are successively brought
into the working position by indexing or rotating the turret. In many
instances, all the tools required can be held in the turret, although it
is often necessary to use other tools, held on a cross-slide, for
cutting off the finished part, facing a radial surface, knurling, or for
some other operation. After a turret lathe is equipped with the tools
needed for machining a certain part, it produces the finished work much
more rapidly than would be possible by using an ordinary engine lathe,
principally because each tool is carefully set for turning or boring to
whatever size is required and the turret makes it possible to quickly
place any tool in the working position. Turret lathes also have systems
of stops or gages for controlling the travel of the turret carriage and
cross-slide, in order to regulate the depth of a bored hole, the length
of a cylindrical part or its diameter; hence, turning machines of this
type are much more efficient than ordinary lathes for turning duplicate
parts, unless the quantity is small, in which case, the advantage of the
turret lathe might be much more than offset by the cost of the special
tool equipment and the time required for "setting up" the machine. (See
"Selecting Type of Turning Machine.")
[Illustration: Fig. 1. Bardons & Oliver Turret Lathe of Motor-driven
Geared-head Type]
=General Description of a Turret Lathe.=--The turret lathe shown in Fig.
1 has a hexagonal shaped turret _A_ with a hole in each side in which
the tools are held. This turret is mounted on a slide _B_ which is
carried by a saddle _C_ that can be moved along the bed to locate the
turret slide with reference to the length of the tools in the turret and
the room required for indexing. The turret slide can be moved
longitudinally by turning the pilot wheel or turnstile _D_, or it can
be fed by power. Ordinarily, the hand adjustment is used for quickly
moving the carriage when the tools are not cutting, although sometimes
the hand feed is preferable to a power feed when the tools are at work,
especially if the cuts are short. After a turret tool has finished its
cut, the turnstile is used to return the slide to the starting point,
and at the end of this backward movement the turret is automatically
indexed or turned one-sixth of a revolution, thus bringing the next tool
into the working position. The turret is accurately located in each of
its six positions by a lock bolt which engages notches formed in a large
index ring at the turret base. A binder lever _E_ at the top of the
turret stud is used to clamp the turret rigidly to the slide when the
tools are cutting.
The forward movement of the slide for each position of the turret is
controlled by stops at _F_, which are set to suit the work being turned.
When parts are being turned from bar stock, the latter passes through
the hollow spindle of the headstock and extends just far enough beyond
the end of the spindle to permit turning one of the parts. The bar is
held while the turning tools are at work, by a chuck of the collet type
at _G_. This chuck is opened or closed around the bar by turning
handwheel _H_. After a finished part has been cut off by a tool held in
cross-slide _J_, the chuck is released and further movement of wheel _H_
causes ratchet feed dog _K_, and the bar which passes through it, to be
drawn forward. This forward movement is continued until the end of the
bar comes against a stop gage held in one of the turret holes, to insure
feeding the bar out just the right amount for turning the next piece. On
some turret lathes, the lever which operates the chuck also controls a
power feed for the bar stock, the latter being pushed through the
spindle against the stop.
The machine illustrated has a power feed for the cross-slide as well as
for the turret. The motion is obtained from the same shaft _L_ which
actuates the turret slide, but the feed changes are independent. The
cross-slide feed changes are varied by levers _M_ and those for the
turret by levers _N_. For many turret lathe operations, such as turning
castings, etc., a jawed chuck is screwed onto the spindle and the work
is held the same as when a chuck is used on an engine lathe. Sometimes
chucks are used having special jaws for holding castings of irregular
shape, or special work-holding fixtures which are bolted to the
faceplate. The small handle at _O_ is for moving the cross-slide along
the bed when this is necessary in order to feed a tool sidewise.
This particular machine is driven by a motor at the rear of the
headstock, connection being made with the spindle through gearing. The
necessary speed changes are obtained both by varying the speed of the
motor and by shifting gears in the headstock. The motor is controlled by
the turnstile _P_ and the gears are shifted by the vertical levers
shown.
While many of the features referred to are common to turret lathes in
general, it will be understood that the details such as the control
levers, arrangement of stops, etc., vary on turret lathes of different
make.
[Illustration: Figs. 2 and 3. Diagrams showing Turret Lathe Tool
Equipment for Machining Automobile Hub Casting]
=Example of Turret Lathe Work.=--The diagrams Figs. 2 and 3 show a
turret lathe operation which is typical in many respects. The part to be
turned is a hub casting for an automobile and it is machined in two
series of operations. The first series is shown by the plan view, Fig.
2. The casting _A_ is held in a three-jaw chuck _B_. Tool No. 1 on the
cross-slide is equipped with two cutters and rough faces the flange and
end, while the inner and outer surfaces of the cylindrical part are
rough bored and turned by combination boring and turning tool No. 2.
This tool has, in addition to a regular boring-bar, a bracket or
tool-holder which projects above the work and carries cutters that
operate on the top surface. Tools Nos. 3 and 4 next come into action,
No. 3 finishing the surfaces roughed out by No. 2, and No. 4
finish-facing the flange and end of the hub. The detailed side view of
Tool No. 3 (which is practically the same as No. 2), shows the
arrangement of the cutters _C_ and _D_, one of which turns the
cylindrical surface and the other bevels the end of the hub. The hole in
the hub is next finished by tool No. 5 which is a stepped reamer that
machines the bore and counterbore to the required size within very
close limits. The surfaces machined by the different tools referred to
are indicated by the sectional view _E_ of the hub, which shows by the
numbers what tools are used on each surface.
For the second series of operations, the position of the hub is reversed
and it is held in a spring or collet type of chuck as shown by the plan
view Fig. 3. The finished cylindrical end of the hub is inserted in the
split collet _F_ which is drawn back into the tapering collet ring by
rod _G_ (operated by turnstile _H_, Fig. 1) thus closing the collet
tightly around the casting. The first operation is that of facing the
side of the flange and end of the hub with tool No. 6 on the
cross-slide, which is shown in the working position. A broad cutter _H_
is used for facing the flange and finishing the large fillet, and the
end is faced by a smaller cutter _I_. When these tools are withdrawn,
tool No. 7 is moved up for rough turning the outside of the cylindrical
end (preparatory to cutting a thread) and rough boring the hole. These
same surfaces are then finished by tool No. 8. The arrangement of tools
Nos. 7 and 8 is shown by the detailed view. Tool _J_ turns the part to
be threaded; tool _K_ turns the end beyond the threaded part; and tool
_L_ bevels the corner or edge. The reaming tool No. 9 is next indexed to
the working position for finishing the hole and beveling the outer edge
slightly. At the same time, the form tool No. 10, held at the rear of
the cross-slide, is fed up for beveling the flange to an angle of 60
degrees. The final operation is that of threading the end, which is done
with die No. 11. The boring-bars of tools Nos. 2, 3, 7 and 8 are all
provided with pilots _N_ which enter close fitting bushings held in the
spindle, to steady the bar while taking the cut. This is a common method
of supporting turret lathe tools.
The feed of the turret for both the first and second series of
operations is 1/27 inch per revolution and the speeds 60 revolutions per
minute for the roughing cuts and 90 revolutions per minute for the
finishing cuts. The total time for machining one of these castings
complete is about 7-1/2 minutes, which includes the time required for
placing the work in the chuck.
=Machining Flywheels in Turret Lathe.=--Figs. 4 to 6, inclusive,
illustrate how a gasoline engine flywheel is finished all over in two
cycles of operations. First the flywheel is turned complete on one side,
the hole bored and reamed, and the outside of the rim finished; in the
second cycle the other side of the flywheel is completed.
[Illustration: Fig. 4. First Cycle of Operations in Finishing Gasoline
Engine Flywheels on a Pond Turret Lathe]
During the first operation, the work is held by the inside of the rim by
means of a four-jaw chuck equipped with hard jaws. The side of the rim,
the tapering circumference of the recess, the web, and the hub are first
rough-turned, using tools held in the carriage toolpost. The hole is
then rough-bored by bar _C_, which is supported in a bushing in the
chuck, as shown in Fig. 4. The outside of the wheel rim is rough-turned
at the same time by a cutter held in the extension turret tool-holder
_T_ (Fig. 5), and the taper fit on the inside of the flywheel is turned
by means of cutter _A_ (Fig. 4) held in a tool-holder attached to the
turret.
The outside of the wheel rim is next finish-turned with cutter _V_ (Fig.
5) held in an extension turret tool-holder the same as the roughing
tool _T_. At the same time, the bore is finished by a cutter in
boring-bar _D_ (Fig. 4). The side of the rim and the hub of the wheel
are also finished at this time by two facing cutters _H_ and _K_, held
in tool-holders on the face of the turret. When the finishing cuts on
the rim and hub are being taken, the work is supported by a bushing on
the boring-bar which enters the bore of the wheel, the boring cutter and
facing tools being set in such relation to each other that the final
boring of the hole is completed before the facing cuts are taken.
[Illustration: Fig. 5. Elevation of Turret and Tools for Finishing
Flywheels--First Operation]
The web of the wheel is next finish-faced with the facing cutter held in
the holder _E_, and the taper surface on the inside of the rim is
finished by the tool _L_, at the same time. While these last operations
are performed, the work is supported by a bushing on a supporting arbor
_J_, which enters the bore of the wheel. The bore is finally reamed to
size by a reamer _F_ held in a "floating" reamer-holder. When the
reaming operation is completed, a clearance groove _N_ is cut on the
inside of the rim, using a tool _G_ held in the carriage toolpost. The
first cycle of operations on the flywheel is now completed.
The flywheel is then removed from the chuck, turned around, and held in
"soft" jaws for the second cycle of operations, the jaws fitting the
outside of the wheel rim. (Soft unhardened jaws are used to prevent
marring the finished surface of the rim.) The operations on this side
are very similar to those performed on the other side. First, the side
of the rim, the inside of the rim, the web, and hub are rough-turned,
using tools held in the carriage toolpost. The inside of the rim and the
web are then finished by a cutter held in a tool-holder at _P_, Fig. 6,
which is bolted to the face of the turret. The work is supported during
this operation by a bushing held on a supporting arbor _U_, having a
pilot which enters a bushing in the chuck. Finally, the rim and hub are
finished, by the facing cutters _R_ and _S_, the work being supported by
an arbor, as before.
[Illustration: Fig. 6. Second Cycle of Operations on Flywheel]
These operations illustrate the methods employed in automobile
factories, and other shops where large numbers of engine flywheels,
etc., must be machined.
=Finishing a Flywheel at One Setting in Turret Lathe.=--The plan view
_A_, Fig. 7, shows an arrangement of tools for finishing a flywheel
complete at one setting. The hole for the shaft has to be bored and
reamed and the hub faced on both sides. The sides and periphery of the
rim also have to be finished and all four corners of the rim rounded.
The tools for doing this work consist of boring-bars, a reamer, facing
heads on the main turret, a turret toolpost on the slide rest
(carrying, in this case, three tools) and a special supplementary wing
rest attached to the front of the carriage at the extreme left.
The casting is held by three special hardened jaws _b_ in a universal
chuck. These jaws grip the work on the inner side of the rim, leaving
room for a tool to finish the rear face without striking the chuck body
or jaws. Three rests _c_ are provided between the chuck jaws. The work
is pressed against these rests while being tightened in the chuck, and
they serve to locate it so that the arms will run true so far as
sidewise movement is concerned. These rests also locate the casting with
relation to the stops for the turret and carriage movements. The chuck
carries a bushing _r_ of suitable diameter to support the boring-bars in
the main turret, as will be described.
In the first operation, boring-bar _m_ is brought in line with the
spindle and is entered in bushing _r_ in the chuck. Double-ended cutter
_n_ is then fed through the hub of the pulley to true up the cored hole.
While boring the hole, the scale on the front face of the rim and hub is
removed by tool _j_. Tool _k_ is then brought into action to rough turn
the periphery, after which tool _e_, in the wing rest, is fed down to
clean up the back face of the rim. As soon as the scale is removed, the
hole is bored nearly to size by cutter _n_{1}_ in bar _m_{1}_, and it is
finally finished with reamer _q_ mounted on a floating arbor.
The cutters _f_, _g_ and _h_, in the facing head, are next brought up to
rough face the hub and rim, and round the corners of the rim on the
front side. This operation is all done by broad shaving cuts. The facing
head in which the tools are held is provided with a pilot bar _t_ which
fits the finished hole in the flywheel hub, and steadies the head during
the operation. The cutters _f_, _g_ and _h_ are mounted in holders which
may be so adjusted as to bring them to the proper setting for the
desired dimensions. This completes the roughing operations.
[Illustration: Fig. 7. Turret Lathe Tool Equipment for Machining
Flywheels]
The periphery of the rim is now finished by cutter _l_ in the turret
toolpost which is indexed to the proper position for this operation. The
rear face of the rim is finished by the same tool _e_ with which the
roughing was done. Tool _e_ is then removed and replaced with _d_
which rounds the inner corner of the rim. Tool _d_ is also replaced with
a third tool for rounding the outer corner of the rear side. For
finishing the front faces of the rim and hub and rounding the corners of
the rim, a second facing head, identical with the first one, is
employed. This is shown in position in the illustration. Cutters
_f_{1}_, _g_{1}_ and _h_{1}_ correspond with the cutters _f_, _g_ and
_h_, previously referred to, and perform the same operations.
The remaining operation of finishing the back of the hub is effected by
cutter _p_. This cutter is removed from the bar, which is then inserted
through the bore; the cutter is then replaced in its slot and the rear
end of the hub is faced by feeding the carriage away from the headstock.
This completes the operations, the flywheel being finished at one
setting.
=Finishing a Webbed Flywheel in Two Settings.=--The plan views _B_ and
_C_, Fig. 7, show the arrangement of tools for finishing a webbed
flywheel which has to be machined all over. This, of course, requires
two operations. In the first of these (see sketch _B_) the rough casting
is chucked on the inside of the rim with regular inside hard chuck jaws
_b_. The cored hole is first rough bored with cutter _n_ attached to the
end of boring-bar _m_, and guided by the drill support _d_ pivoted to
the carriage. Next, the boring-bar _m_{1}_ is brought into position, the
drill support being swung back out of the way. This bar is steadied by
its bearing in bushing _r_ in the chuck. Two cutters, _n_{1}_ and
_n_{2}_, are used to roughly shape the hole to the desired taper, the
small end being finished to within 0.002 inch of the required diameter.
While boring with the bar _m_{1}_, the scale is broken on the web and
hub of the casting by the tool _k_ in the turret toolpost. The latter is
then shifted to bring the tool _j_ into position for removing the scale
on the periphery of the wheel. Next, the hole is reamed with taper
reamer _q_, the pilot of which is supported by bushing _r_.
The first of the facing heads is now brought into action. This facing
head carries a guide _t_ which is steadied in a taper bushing _c_,
driven into the taper hole of the hub for that purpose. The top cutter
_f_ turns the periphery, cutter _g_ turns the hub and faces the web,
and cutter _h_ faces the rim. A fourth cutter _e_ on the under side of
the head faces the hub. This casting is now machined approximately to
size.
For finishing, similar cutters, _e_{1}_, _f_{1}_, _g_{1}_ and _h_{1}_,
in the other facing head are used, the latter being supported by the
taper bushing _c_ in the same way. A very light cut is taken for
finishing. Tool _l_ in the carriage turret is used to round the outer
and inner corners of the rim, which completes the work on this face of
the casting.
In the second cycle of operations, shown at _C_, the casting is chucked
on the outside with the soft jaws _b_, which are bored to the exact
diameter of the finished rim. The work is further supported and centered
by sliding bushing _c_, which is tapered to fit the finished hole in the
hub, and has an accurate bearing in bushing _r_ in the chuck. This
bushing is provided with a threaded collar for forcing it into the work
and withdrawing it. The scale on the web and the inside and face of the
rim is first broken with the tool _k_ in the turret toolpost. These
surfaces are then roughed off with cutters _f_, _g_ and _h_, in the
facing head. This latter is steadied by a pilot _t_ which enters the
hole in the sliding bushing _c_ on which the work is supported. A light
cut is next taken with cutters _f_{1}_, _g_{1}_ and _h_{1}_, in the
finishing facing head, which completes the operation.
=Tools for Turret Lathes.=--The operation of a turret lathe after the
tools have been properly arranged is not particularly difficult, but
designing and making the tools, determining what order of operations
will give the most efficient and accurate results, and setting the tools
on the machine, requires both skill and experience. For some classes of
work, especially if of a rather complicated nature, many of the tools
must be specially designed, although there are certain standard types
used on turret lathes which are adapted to general turning operations.
Some of the principal types are referred to in the following.
=Box-tools.=--Tools of this type are used for turning bar stock. There
are many different designs, some of which are shown in Figs. 8, 9 and
10. Box-tools are held in the turret and they have back-rests opposite
the turning tools, for supporting the part being turned. The box-tool
shown at _A_, Fig. 8, is for roughing. The cutter _a_ is a piece of
high-speed steel beveled on the cutting end to produce a keen edge. It
takes a shearing tangent cut on top of the bar and the latter is kept
from springing away by means of the adjustable, hardened tool-steel
back-rest _b_. This tool is considered superior to a hollow mill
whenever a fair amount of stock must be removed. If considerable
smoothness and accuracy are necessary, the finishing box-tool shown at
_B_ should follow the roughing box tool, but in most cases, especially
if the part is to be threaded by a die, a finishing cut is unnecessary.
[Illustration: Fig. 8. Different Types of Box-tools for Turret Lathe]
The finishing box-tool _B_ is also used to follow a hollow mill if
special accuracy or smoothness is desired. This tool is only intended
for light finishing cuts, the allowances varying from 0.005 inch to
0.015 inch in diameter. The cutters are made of square tool steel of
commercial size, and are ground and set to take a scraping end cut. This
particular tool has two tool-holders which permit finishing two
diameters at once. If a larger number of sizes must be turned, extra
tool-holders can be applied.
The single-cutter box-tool shown at _C_ is bolted directly to the face
of the turret instead of being held by a shank in the turret hole, and
it is adapted for heavy cuts such as are necessary when turning
comparatively large bar stock. The tool-holder _a_ swivels on a stud,
thus allowing the cutter to be withdrawn from the work while being
returned, which prevents marring the turned surface. The high-speed
steel cutter is ground to take a side cut on the end of the bar. The
latter is supported by hardened and ground tool-steel rolls _b_ which
revolve on hardened and ground studs. These rolls are mounted on
swinging arms which have a screw adjustment for different diameters.
They can also be adjusted parallel to the bar, thus enabling them to be
set either in advance of or back of the cutter. The opening in the base
allows the stock to pass into the turret when it is not larger than the
turret hole.
The box-tool shown at _D_ is similar to the one just described, except
that it has two or more cutters and roller back-rests, thus enabling
different diameters to be turned simultaneously. The cutters are ground
to take a side cut. Ordinarily this gives a satisfactory finish, but if
special accuracy and smoothness are desired, two tools should be used,
one for roughing and one for finishing, the latter being ground to take
a light scraping end cut.
The taper-turning box-tool shown at _E_ is designed for accurately
turning tapers on brass or cast-iron parts, when there is a small amount
of stock to be removed. The taper is obtained by cross motion imparted
to the cutter slide as the turret advances. The taper-turning box-tool
shown at _F_, instead of having a single-point cutter, is provided with
a wide cutter _a_. This tool is designed to turn tapering parts of
small or medium diameter, requiring the use of a support which cannot be
provided with a straight forming tool and holder mounted on the cut-off
slide. The cutter is backed up by the screws shown, which also provide
adjustment for different tapers within a limited range. The bar is
supported by the three back-rests shown, which also have screw
adjustment.
=Examples of Box-tool Turning.=--Box-tools are not only used for
cylindrical and taper turning on the end of a bar, but for many other
operations. Figs. 9 and 10 show a number of box-tools of different
designs, with examples of the work for which each is intended. While
these tools are designed for some specific part, they can, of course,
with slight modifications be adapted to other work.
[Illustration: Fig. 9. Box-tools and Work for which they are Intended]
A box-tool of the pilot type that is used for finishing, after the
surplus stock has been removed by roughing tools, is shown at _A_, Fig.
9. The work, which is the cone for a ball bearing, is shown at _a_ by
the dotted lines and also by the detail view to the right. The pilot _b_
enters the work before either of the cutters begins to operate on its
respective surface. The inverted cutter _c_, which sizes the flange of
the cone, is held in position by a clamp _d_, which is forced down by a
collar-head screw. The cutter is further secured against a beveled
shoulder at _g_ by the set-screws _f_, and it is adjusted forward by the
screw _e_. By loosening the screws _f_ and the collar-head screw, the
cutter may be removed for sharpening. The cutter _h_ is adjusted to cut
to the proper diameter, by the screws _l_, after which the clamp _k_ is
made level by the screw _j_. The collar-screw _m_ is then used to secure
the tool in place. The cutter is made from drill rod and it is slightly
cupped out on the cutting end to give keenness to the cutting edge. The
adjusting screw _o_, which passes through plate _p_, prevents the cutter
from backing away from the work. This adjusting screw plate has its
screw holes slotted to avoid removing the screws when it becomes
necessary to remove the plate and cutter for sharpening. Pilot _b_ is
held firmly to the tool body by set-screw _r_. The hole _s_ through the
shank makes it easy to remove the pilot, in case this is necessary.
A pilot box-tool for finishing another type of ball bearing cone is
shown at _B_. The shape of the work itself is indicated by the dotted
lines _a_ and by the detail view. This tool is somewhat similar in its
construction to the one just described. The cutters _b_ and _c_ are
inverted and are used to face the flange at _d_ and to turn it to the
proper diameter. These cutters are held by the clamp _f_ and screws _g_
and are adjusted forward by the screw _h_. The cutter _j_, which
operates on top of the stock, rests on a bolster, of the proper angle
and is adjusted up or down by the screws _k_. The clamp _l_, which binds
against this tool, is beveled to correspond with the angle of the tool.
This clamp is secured by the collar-screw shown and it is leveled by
set-screws _s_. The adjusting screw _p_ prevents the cutter from
slipping back. The holes in the adjusting-screw plate are also slotted
in this case so that it will not be necessary to remove any screws when
the cutter has to be taken out of the holder.
A box-tool for finishing a treadle-rod cone for a sewing machine is
shown at _C_. This tool is also of the pilot type. The cutters in it
operate on opposite sides of the cone _a_. The inverted cutter _b_ sizes
the cylindrical part of the cone, while the front cutter _d_ is set at
the proper angle to finish the tapered part. The rear cutter _b_ is held
in place by the clamp _g_ and a collar screw. It is adjusted forward by
the screw _h_ in the plate _i_ which is held by screws as shown. The
pilot is retained by a set-screw, and it is easily removed by inserting
a small rod in the hole _l_ which passes through the shank. The cutter
_d_ is held by clamp _m_ and is adjusted by screw _n_ which passes
through a tapped hole in plate _o_. The screw holes in both the
adjusting plates _i_ and _o_ are slotted to facilitate their removal.
The box-tool illustrated at _A_, Fig. 10, is used for finishing the
bushing of a double-taper cone bearing _a_. The cutters are so arranged
that they all cut on the center; that is, the cutting edges lie in a
horizontal plane. The inverted cutter _b_ at the rear forms the short
angular surface, and the cutter _c_ in front forms the long tapering
part of the bearing. The large diameter is turned, to size by cutter
_d_. The pilot _e_ has a bearing in the bore nearly equal to the length
of the work and it is provided with oil grooves, as shown. The taper
shank of this pilot is tapped for the screw _i_ which extends the whole
length of the shank and is used to draw the pilot back to its seat. It
is not necessary to remove adjusting-screw plate _k_ to take out the
cutter _b_, as the latter can be drawn out from the front after the
collar-screw _m_ is loosened. The cutter _c_ is removed by taking off
the adjusting-screw plate _s_ after loosening the collar-screw _n_. The
cutter _d_ is held in a dove-tailed slot by two headless set-screws _q_.
It is also backed up by an adjusting screw in the plate _s_. These
adjusting screws should all have fine threads, say from 32 to 40 per
inch, and be nicely fitted so they will not loosen after being adjusted.
The box-tools shown at _B_ and _C_, Fig. 10, are for turning the sides
of a loose pulley for a sewing machine. This pulley (shown by the dotted
lines) is finished in two operations. The box-tool for finishing the
side of the pulley on which the hub projects beyond the rim, is shown at
_B_. The inverted cutter _a_, which faces the end of the hub, is held by
a clamp _c_ (clearly shown in the end view) from the under side and it
has no adjustment. The collar-screw _d_ is tapped into this clamp, which
is prevented from getting out of place by the dowel-pin _f_. The pilot
_g_ is made small in the shank, so that tool _a_ can be so placed as to
insure the removal of all burrs around the bore of the hub. The pilot is
held by a set-screw and it is provided with oil grooves. The cutter _j_
sizes the outside of the hub, and the cutter _k_ faces the side of the
pulley rim. These cutters are both held by the clamp _l_ and the
collar-screw _m_. No side plates are used on this tool, and the cutters
are all easily removed.
[Illustration: Fig. 10. Examples of Box-tool Designs]
Sketch _C_ shows the box-tool used for the second operation. As the hub
is flush with the rim on the side for which this tool is intended, it
needs only one cutter to face both. This is done by the wide cutter _a_
which is held in a dove-tailed slot in the front of the tool and is
fastened by the clamp _b_ and collar-screw _c_. The bushing _d_, in
which the end of the work arbor is supported, is held by the
collar-screw _e_, and to obtain the necessary compression, the body of
the tool is slotted as far back as _f_. This bushing is provided with
oil grooves and one side is cut away to clear the cutter _a_. The
pilot end of the arbor on which the work is mounted is 1/16 inch smaller
than the bore of the pulley, which allows the cutter to be set in far
enough to prevent any burr which might form at the edge of the bore. A
disk _i_ is inserted back of bushing _d_, so that the latter may be
easily removed by passing a rod through the hollow shank. The special
chuck used for this second operation on the loose pulley is screwed onto
the spindle, and the work is mounted on a projecting arbor and driven by
the pins engaging holes in the pulley web. The arbor is made a driving
fit for the work, and the end or pilot is a running fit in the bushing
of the box-tool. A counterbore in the arbor hub provides clearance for
the hub of the pulley which projects beyond the rim on one side.
[Illustration: Fig. 11. (A) Hollow Mill and Holder. (B) Spring
Screw-threading Die and Releasing Die-holder]
=Hollow Mills.=--A hollow mill such as is shown at _A_ in Fig. 11 is
sometimes used in place of a box-tool (especially when turning brass)
for short roughing cuts preceding a threading operation. The turning is
done by the cutting edges _e_, and the turned part enters the mill and
is steadied by it. If this type of tool is used for long, straight cuts,
especially on square stock and when making screws with large heads from
the bar, it should always be followed by a finishing box-tool to insure
accurate work. A hollow mill can be sharpened readily by grinding the
ends without materially changing the cutting size. A slight adjustment
can be obtained by means of the clamp collar shown to the left, although
this is not generally used. When making these mills, they should be
reamed out tapering from the rear to give clearance to the cutting
edges. For turning steel, the cutting edge should be about 1/10 of the
diameter ahead of the center, whereas for brass, it should be on the
center-line.
[Illustration: Fig. 12. Geometric Adjustable Hollow Milling Tool]
Hollow mills are also made adjustable. The design shown in Fig. 12 is
especially adapted for brass finishing. It can also be used for taking
light cuts on cast iron or steel but its use in place of roughing or
finishing box-tools for general use is not recommended. With the
exception of the cutters and screws, the complete tool consists of three
parts, _viz._, the holder, cam, and ring. The cam serves to adjust the
cutters for different diameters. The adjustment is made by the two
screws shown, the amount being indicated by a micrometer scale. When
adjusting the cutters for a given diameter, the use of a hardened steel
plug of the required size is advisable, the cutters being adjusted
against the plug.
=Releasing Die and Tap Holders.=--Threads are cut in the turret lathe by
means of dies for external threading, and taps for internal threading,
the die or tap being held in a holder attached to the turret. A simple
form of releasing die holder is shown at _B_, Fig. 11. This holder was
designed for the spring-screw type of threading die shown to the left.
The die is clamped in the holder _a_ by the set-screw shown, and the
shank _b_ of the holder is inserted in the turret hole. Holder _a_ has
an extension _c_ which passes through the hollow shank. When the die is
pressed against the end of the work, holder _a_ and its extension moves
back until lug _d_ on the holder engages lug _e_ on the shank. The die
and holder are then prevented from rotating with the work and the die
begins to cut a thread. It continues to screw itself onto the work with
the turret following, until the thread has been cut to the required
length; the turret is then stopped and as the die and holder _a_ are
drawn forward, lugs _d_ and _e_ disengage so that the die simply rotates
with the work without continuing to advance. The lathe spindle is then
reversed and as the turret is moved back by hand, pin _f_ comes around
and enters notch _g_, thus holding the die stationary; the die then
backs off from the threaded end. Some tap holders are also constructed
the same as this die holder, so far as the releasing mechanism is
concerned. There are also many other designs in use, some of which
operate on this same principle.
[Illustration: Fig. 13. Geometric Self-opening and Adjustable
Screw-cutting Die Head]
=Self-opening Die Heads.=--The type of die holder shown at _B_ in Fig.
11 is objectionable because of the time required for backing the die off
the threaded end; hence, self-opening dies are extensively used in
turret lathe work. As the name implies, this type of die, instead of
being solid, has several chasers which are opened automatically when the
thread has been cut to the required length. The turret can then be
returned without reversing the lathe spindle. The dies are opened by
simply stopping the travel of the turret slide, the stop-rod for the
feed of the turret being adjusted to give the proper amount of travel.
[Illustration: Fig. 14. Geometric Collapsing Tap]
A well-known die head of the self-opening type is shown in Fig. 13. The
dies open automatically as soon as the travel of the head is retarded,
or they can be opened at any point by simply holding back on the
turnstile or lever by which the turret slide is moved. The die is closed
again by means of the small handle seen projecting at right-angles from
the side of the head. The closing may be done by hand or automatically
by screwing a pin into a threaded hole opposite the handle and attaching
a small piece of flat steel to the back edge of the turret slide. The
latter will then engage the pin as the turret revolves, thus closing the
die head. This die head has a roughing and finishing attachment which is
operated by handle _A_. When this handle is moved forward, the dies are
adjusted outward 0.01 inch for the roughing cut, whereas returning the
handle closes and locks the dies for the finishing cut. The die head has
a micrometer scale which is used when making slight adjustments to
compensate for the wear of the chasers or to make either a tight-or a
loose-fitting thread.
=Collapsing Taps.=--The collapsing tap shown in Fig. 14 is one of many
different designs that are manufactured. They are often used in turret
lathe practice in place of solid taps. When using this particular style
of collapsing tap, the adjustable gage _A_ is set for the length of
thread required. When the tap has been fed to this depth, the gage comes
into contact with the end of the work, which causes the chasers to
collapse automatically. The tool is then withdrawn, after which the
chasers are again expanded and locked in position by the handle seen at
the side of the holder. In all threading operations, whether using taps
or dies, a suitable lubricant should be used, as a better thread is
obtained and there is less wear on the tools. Lard oil is a good
lubricant, although cheaper compounds give satisfactory results on many
classes of work.
=Miscellaneous Turret Lathe Tools.=--The chamfering tool shown at _A_,
Fig. 15, is used for pointing the end of a bar before running on a
roughing box-tool. This not only finishes the end of the bar but
provides an even surface for the box-tool to start on. The cutter is
beveled on the end to form a cutting edge and it is held at an angle.
The back-rest consists of a bell-mouthed, hardened tool-steel bushing
which supports the bar while the cut is being taken.
The stop gages _B_ and _C_ are used in the turret to govern the length
of stock that is fed through the spindle. When a finished piece has been
cut off, the rough bar is fed through the spindle and up against the
stop gage, thus locating it for another operation. This gage may be a
plain cylindrical piece of hardened steel, as at _B_, or it may have an
adjusting screw as at _C_; for special work, different forms or shapes
are also required. The stop gages on some machines, instead of being
held in the turret, are attached to a swinging arm or bracket that is
fastened to the turret slide and is swung up in line with the spindle
when the stock is fed forward.
The center drilling tool _D_ is designed to hold a standard combination
center drill and reamer. This type of tool is often used when turning
parts that must be finished afterwards by grinding, to form a center for
the grinding machine. The adjustable turning tool _E_ is used for
turning the outside of gear blanks, pulley hubs or the rims of small
pulleys. The pilot _a_ enters the finished bore to steady the tool, and
cutter _b_ is adjusted to turn to the required diameter.
[Illustration: Fig. 15. Various Types of Tools for the Turret Lathe]
The cutting-off tool-holder _F_ (which is held on the cross-slide of the
turret lathe) is usually more convenient than a regular toolpost, as the
blade can be set closer to the chuck. The blade is held in an inclined
position, as shown, to provide rake for the cutting edge; the inclined
blade can also be adjusted vertically, a limited amount, by moving it in
or out. The multiple cutting-off tool _G_ holds two or more blades and
is used for cutting off several washers, collars, etc., simultaneously.
By changing the distance pieces between the cutters, the latter are
spaced for work of different widths. The flat drill holder _H_ is used
for drilling short holes, and also to form a true "spot" or starting
point for other drills.
Knurling tools are shown at _I_ and _J_. The former is intended for
knurling short lengths and is sometimes clamped on top of the cut-off
tool on the cross-slide, the end being swung back after knurling (as
shown by the dotted lines) to prevent interference with the work when
the cutting-off tool is in operation. The knurling tool _J_ has a shank
and is held in the turret. The two knurls are on opposite sides of the
work so that the pressure of knurling is equalized. By adjusting the
arms which hold the knurls, the tool can be set for different diameters.
Three styles of drill holders are shown at _K_, _L_ and _M_. Holder _K_
is provided with a split collet (seen to the left) which is tightened on
the drill shank by a set-screw in the holder. This holder requires a
separate collet for each size drill. The taper shank drill holder _L_
has a standard taper hole into which the shank of the drill is inserted.
The adjustable type of holder _M_ is extensively used, especially on
small and medium sized machines when several sizes of drills are
necessary. This holder is simply a drill chuck fitted with a special
shank. For large drills the plain style of holder _K_ is recommended,
and if only a few sizes of drills are required, it is more satisfactory
and economical than the adjustable type.
The various types of small turret lathe tools referred to in the
foregoing for turning, threading, tapping, knurling, etc., are a few of
the many different designs of tools used in turret lathe practice.
Naturally, the tool equipment for each particular job must be changed
somewhat to suit the conditions governing each case. The tools referred
to, however, represent in a general way, the principal types used in
ordinary practice. Some of the more special tools are shown in
connection with examples of turret lathe work, which are referred to in
the following.
=Turning Gasoline Engine Pistons in Turret Lathe.=--The making of
pistons for gas engines, especially in automobile factories, is done on
such a large scale that rapid methods of machining them are necessary.
The plan view _A_, Fig. 16, shows the turret lathe tools used in one
shop for doing this work. As is often advisable with work done in large
quantities, the rough castings are made with extra projections so
arranged as to assist in holding them. These projections are, of course,
removed when the piece is completed. In this case the piston casting _a_
has a ring about 1-1/4 inch long and a little less in diameter than the
piston, at the chucking end. The piston is held in suitable chuck jaws
_b_ which are tightened against the inside of this ring. The set-screws
in these special jaws are then tightened, thus clamping the casting
between the points of the screws and the jaws. This method of holding
permits the whole exterior of the piston to be turned, since it projects
beyond the chuck jaws. This is the object in providing the piston with
the projecting ring by which it is held.
[Illustration: Fig. 16. (A) Method of Boring and Turning Pistons in
Gisholt Lathe. (B) Special Chuck and Tools for Turning, Boring and
Cutting Off Eccentric Piston Rings]
The first operation consists in rough-boring the front end of the
piston. The double-ended cutter _n_ is held in boring-bar _m_, which is,
in turn, supported by a drill-holder, clamped to one of the faces of
the turret. This bar is steadied by a bushing in the drill support _c_
which is attached to the carriage, and may be swung into or out of the
operating position, as required. After this cut is completed, the turret
is revolved half way around and the casting is finish-bored in a similar
manner, with double-ended cutter _n_{1}_ held in bar _m_{1}_, the drill
support being used as in the previous case. The support is then turned
back out of the way to allow the turning tools in the turret toolpost to
be used.
The outside of the piston is next rough-turned with tool _k_ in the
turret toolpost, which is revolved to bring this cutter into action. The
toolpost is then turned to the position shown, and the outside is
finish-turned by tool _j_, which takes a broad shaving cut. The turret
tool-holder is again revolved to bring form tool _l_ into position. This
tool cuts the grooves for the piston rings. Suitable positive stops are,
of course, provided for both the longitudinal and cross movements of the
turret toolpost.
In the second operation, the piston _a_ is reversed and held in soft
jaws, which are used in place of the hardened jaws _b_ shown in the
illustration. These jaws are bored to the outside diameter of the
piston, so that when closed, they hold the work true or concentric with
the lathe spindle. In this operation the chucking ring by which the
piston was previously held is cut off, and the end of the piston is
faced true. If the crank-pin hole is to be finished, a third operation
is necessary, a self-centering chuck-plate and boring and reaming tools
being used. (These are not shown in the illustration.)
=Turning Piston Rings in Turret Lathe.=--One method of turning piston
rings is shown at _B_ in Fig. 16. The piston rings are cut from a
cast-iron cylindrical piece which has three lugs _b_ cast on one end and
so arranged that they may be held in a three-jawed chuck. This
cylindrical casting is about 10 inches long, and when the rings are to
have their inside and outside surfaces concentric, the casting is held
by the lugs in the regular jaws furnished with the chuck. (The
arrangement used for turning and boring eccentric rings, which is that
shown in the illustration, will be described later.)
The casting _a_, from which the rings are made, is first rough-bored
with double-ended cutter _n_ in boring-bar _m_, after which it is
finish-bored with cutter _n_{1}_ in bar _m_{1}_. While taking these
cuts, the bars _m_ and _m_{1}_ are supported by their extension ends
which enter bushing _r_ located in the central hole of the chuck. This
furnishes a rigid support so that a heavy cut can be taken.
The outside of the casting is next rough-turned with tool _k_, held in
the turret toolpost. This toolpost is then revolved to bring tool _j_
into position, by which the outside is turned true to size, a broad
shaving chip being taken. The toolpost is again swung around, to bring
the cutting-off tool-holder _l_ into position. This holder contains four
blades set the proper distance apart to give rings of the desired width.
Each blade, from right to left, is set a little back of the preceding
one, so that the rings are cut off one after the other, the outer rings
being supported until they are completely severed. After the first four
rings are cut off, the carriage is moved ahead to a second stop, and
four more rings are severed, this operation being continued until the
casting has been entirely cut up into rings.
When the bore of the ring is to be eccentric with the outside, the
holding arrangement shown in the illustration is used. The casting a is
bolted to a sliding chuck-plate _c_, and the outside is rough-turned
with tool _k_ in the toolpost. Finishing tool _j_ is then brought into
action, and the outside diameter is turned accurately to size. Then the
sliding chuck-plate _c_, carrying the work, is moved over a distance
equal to the eccentricity desired, and the work is bored with cutters
_n_ and _n_{1}_ as in the previous case. The turret toolpost is next
revolved and the tools _l_ are used for cutting off the rings. The
reason for finishing the outside first is to secure smooth rings in
cutting off, as this operation should be done when the work is running
concentric with the bore, rather than with the exterior surface.
It will be evident that this method gives a far greater output of rings
than is possible by finishing them in the more primitive way on engine
lathes. The faces of the rings may be finished in a second operation if
desired, or they may be ground, depending on the method used in the
shop where the work is being done, and the accuracy required.
[Illustration: Fig. 17. Turning Gasoline Engine Pistons in Pratt &
Whitney Turret Lathe]
=Piston Turning in Pratt and Whitney Turret Lathe.=--A turret lathe
equipped with tools for turning, facing and grooving automobile gasoline
engine pistons is shown in Fig. 17. The piston is held on an expanding
pin chuck which is so constructed that all of the pins are forced
outward with equal pressure and automatically conform to any
irregularities on the inside of the piston. Tool _A_ rough-turns the
outside, and just as this tool completes its cut, a center hole is
drilled and reamed in the end of the piston by combination drill and
reamer _B_. The turret is then indexed one-half a revolution and a
finishing cut is taken by tool _C_. After the cylindrical body of the
piston has been turned, tools held in a special holder _E_ attached to
the cut-off slide are used to face the ends of the piston and cut the
packing-ring grooves. While the grooves are being cut, the outer end of
the piston is supported by center _D_. The center hole in the end also
serves to support the piston while being ground to the required diameter
in a cylindrical grinding machine. The edge at the open end of the
piston may also be faced square and the inner corner beveled by a hook
tool mounted on the rear cross-slide, although this is usually done in a
separate operation. (This provides a true surface by which to hold this
end when grinding.)
[Illustration: Fig. 18. Pratt & Whitney Turret Lathe equipped with
Special Attachment for Turning Eccentric Piston Rings]
This illustration (Fig. 17) shows very clearly the stops which
automatically disengage the turret feed. A bracket _F_ is bolted to the
front of the bed and contains six stop-rods _G_ (one for each position
or side of the turret). When one of these stop-rods strikes lever _H_,
the feed is disengaged, the stop being adjusted to throw out the feed
when the tool has completed its cut. Lever _H_ is automatically aligned
with the stop-rods for different sides of the turret by a cam _J_ on the
turret base. A roller _K_ bears against this cam and, through the
connecting shaft and lever shown, causes lever _H_ to move opposite the
stop-rod for whatever turret face is in the working position. Lever _L_
is used for engaging the feed and lever _R_ for disengaging it by hand.
The indexing of the turret at the end of the backward movement of the
slide is controlled by stop _M_ against which rod _N_ strikes, thus
disengaging the lock bolt so that the turret can turn. This stop _M_ is
adjusted along the bed to a position depending upon the length of the
turret tools and the distance the turret must move back to allow the
tools to clear as they swing around.
[Illustration: Fig. 19. Tool Equipment for Machining Worm Gear
Blanks--Davis Turret Lathe]
=Attachment for Turning Piston Rings.=--Fig. 18 shows a special
attachment applied to a Pratt & Whitney turret lathe for turning
eccentric, gas-engine piston rings. The boring of the ring casting,
turning the outside and cutting off the rings, is done simultaneously.
The interior of the casting is turned concentric with the lathe spindle
by a heavy boring-bar, the end of which is rigidly supported by a
bushing in the spindle. The slide which carries the outside turning tool
is mounted on a heavy casting which straddles the turret. The outside of
the ring casting is turned eccentric to the bore as a result of an
in-and-out movement imparted to the tool by a cam on shaft _A_ which is
rotated from the lathe spindle through the gearing shown. For each
revolution of the work, the tool recedes from the center and advances
toward it an amount sufficient to give the required eccentricity. When
the turning and boring tools have fed forward about 2 inches, then the
cutting-off tools which are held in holder _B_ come into action. The end
of each cutting-off tool, from right to left, is set a little farther
away from the work than the preceding tool, so that the end rings are
always severed first as the tools are fed in by the cross-slide. A
number of the completed rings may be seen in the pan of the machine.
[Illustration: Fig. 20. Turning Bevel Gear Blanks in Davis Turret
Lathe--First Operation]
=Turning Worm-gear Blanks in Turret Lathe.=--This is a second operation,
the hub of worm-gear blank _G_ (Fig. 19) having previously been bored,
reamed, and faced on the rear side. The casting is mounted upon a
close-fitting arbor attached to a plate bolted to the faceplate of the
lathe, and is driven by two pins which engage holes on the rear side.
The rim is first rough-turned by a tool _A_ which operates on top, and
the side is rough-faced by a toothed or serrated cutter _B_. A similar
tool-holder having a tool _C_ and a smooth cutter _D_ is then used to
turn the rim to the required diameter and finish the side. The end of
the hub is faced by cutters mounted in the end of bars _E_ and _F_, one
being the roughing cutter and the other the finishing cutter. The work
arbor projects beyond the hub, as will be seen, and forms a pilot that
steadies these cutter bars. The curved rim of the gear is turned to the
required radius (preparatory to gashing and bobbing the worm-wheel
teeth) by a formed tool _H_ held on the cross-slide.
[Illustration: Fig. 21. Second Operation on Bevel Gear Blanks]
=Turning Bevel Gear Blanks.=--Fig. 20 shows a plan view of the tools
used for the first turning operation on bevel gear blanks (these gears
are used for driving drill press spindles). The cored hole is beveled
true at the end by flat drill _A_ to form a true starting surface for
the three-fluted drill _B_ which follows. The hole is bored close to the
required size by a tool (not shown) held in the end of bar _C_, and it
is finished by reamer _D_. The cylindrical end of the gear blank or hub
is rough-and finish-turned by tools held in holders _E_ and _F_,
respectively. (These holders were made to set at an angle of 45 degrees,
instead of being directly over the work, as usual, so that the cutters
would be in view when setting up the machine.) It will be noted that the
chuck is equipped with special jaws which fit the beveled part of the
casting.
[Illustration: Fig. 22. Sectional View of Tapering Mold Shell which is
turned in Hartness Flat Turret Lathe, as illustrated in Figs. 23 to 27,
Inclusive]
The second and final operation on this blank is shown in Fig. 21. The
work _A_ is held by a special driver plate attached to the faceplate of
the machine. This driver plate has two pins which engage holes drilled
in the gear blank and prevent it from rotating. The blank is also held
by a bolt _B_ which forces a bushing against the cylindrical end. First,
the broad beveled side which is to be the toothed part of the gear, is
rough-turned by toothed cutters _C_, and a recess is formed in the end
of the blank, by a turning tool in this same tool-holder. A similar
tool-holder _E_, having finishing cutters, is then used to finish the
bevel face and recess. The other tools seen in the turret are not used
for this second operation. The rear bevel is roughed and finished by
tools and held on the cross-slide.
=Shell Turning Operation in Flat Turret Lathe.=--The "flat turret lathe"
is so named because the turret is a flat circular plate mounted on a low
carriage to secure direct and rigid support from the lathe bed. The
tools, instead of being held by shanks inserted in holes in the turret,
are designed so that they can be clamped firmly onto the low circular
turret plate.
An interesting example of flat turret lathe work is shown in Fig. 22.
This is a steel shell which must be accurately finished to a slight
taper, both inside and out, threaded and plain recesses are required at
the ends, and, in addition, one or two minor operations are necessary.
This work is done in the Hartness flat turret lathe, built by the Jones
& Lamson Machine Co. The shells are turned from cold-drawn seamless
steel tubing, having a carbon content of 0.20 per cent, and they are
finished at the rate of one in nine minutes. The tubing comes to the
machine in 12-foot lengths, and the tube being operated upon is, of
course, fed forward through the hollow spindle as each successive shell
is severed.
[Illustration: Fig. 23. First Operation on Shell Illustrated in Fig.
22--Rough-turning and Boring]
In finishing this shell, five different operations are required. During
the first operation the shell is rough-bored and turned by one passage
of a box-tool, Fig. 23, and the recess _A_, Fig. 22, at the outer end,
is finished to size by a second cutter located in the boring-bar close
to the turret. The turret is then indexed to the second station which
brings the threading attachment _G_ into position, as shown in Fig. 24.
After the thread is finished, the recess _B_, Fig. 22, is turned by a
flat cutter _K_, Fig. 25. The inner and outer surfaces are then finished
to size by a box-tool mounted on the fourth station of the turret and
shown in position in Fig. 26. The final operation, Fig. 27, is performed
by three tools held on an auxiliary turret cross-slide, and consists in
rounding the corners at _b_ and _c_, Fig. 22, and severing the finished
shell.
[Illustration: Fig. 24. Second Operation--Cutting Internal Thread]
One of the interesting features connected with the machining of this
shell is the finishing of the inner and outer tapering surfaces. The
taper on the outside is 3/32 inch Per foot, while the bore has a taper
of only 1/64 inch per foot, and these surfaces are finished
simultaneously. The box-tool employed is of a standard type, with the
exception of an inserted boring-bar, and the taper on the outside is
obtained by the regular attachment which consists of a templet _D_ (Fig.
23) of the required taper, that causes the turning tool to recede at a
uniform rate as it feeds along. To secure the internal taper, the
headstock of the machine is swiveled slightly on its transverse ways by
the use of tapering gibs. By this simple method, the double taper is
finished to the required accuracy without special tools or equipment.
As those familiar with this machine know, the longitudinal movements of
the turret as well as the transverse movements of the headstock are
controlled by positive stops. The headstock of this machine has ten
stops which are mounted in a revolving holder and are brought into
position, as required, by manipulating a lever at the front. The stops
for length, or those controlling the turret travel, are divided into two
general groups, known as "A" and "B". Each of these groups has six stops
so that there are two stops for each of the six positions or stations of
the turret, and, in addition, five extra stops are available for any one
tool, by the engagement of a pin at the rear of the turret. The change
from the "A" to the "B" stops is made by adjusting lever _L_, Fig. 26,
which also has a neutral position.
[Illustration: Fig. 25. Third Operation--Turning Recess at Rear End;
Tool is shown withdrawn]
After the box-tool for the roughing cut, shown at work in Fig. 23, has
reached the end of its travel, further movement is arrested by a stop of
the "A" group. The outside turning tool is then withdrawn by operating
lever _E_ and the turret is run back and indexed to the second station,
thus bringing the threading attachment into position. The surface speed
of 130 feet per minute which is used for turning is reduced to about 30
feet per minute for threading by manipulating levers _H_, Fig. 24. After
the turret is located by another stop of the "A" group, the threading
attachment is made operative by depressing a small plunger _I_, which
connects a vertical driving shaft from the spindle with the splined
transmission shaft _J_. A reciprocating movement is then imparted to the
thread chaser _t_ which advances on the cutting stroke and then
automatically retreats to clear the thread on the return. This movement
is repeated until the thread is cut to the proper depth, as determined
by one of the stops for the headstock. While the thread is being cut,
the carriage is locked to the bed by the lever _N_, Fig. 26. It was
found necessary to perform the threading operation before taking the
outside finishing cut, owing to a slight distortion of the shell wall,
caused by the threading operation.
[Illustration: Fig. 26. Fourth Operation--Finishing the Bore and
Outside]
After the thread is finished, the turret is turned to the third station
as shown in Fig. 25, and tool _K_ for the inner recess _B_, Fig. 22, is
brought into position and fed to the proper depth, as determined by
another cross-stop. The turret is also locked in position for this
operation. The finishing cuts for the bore and the outside are next
taken by a box-tool which is shown near the end of its cut in Fig. 26.
This box-tool is similar to the one used for roughing, but it is
equipped with differently shaped cutters to obtain the required finish.
The outside turning tool has a straight cutting edge set tangent to the
cylindrical surface and at an angle, while the boring tool has a cutting
edge of large radius. An end view of this box-tool is shown in Fig. 27.
A reduced feed is employed for the finishing cut, and the speed is
increased to 130 feet per minute, which is the same as that used for
roughing.
[Illustration: Fig. 27. Fifth Operation--Rounding Ends, Scoring Large
End, and Cutting Off]
During the next and final operation, the turret, after being indexed to
the position shown in Fig. 27, is first located by a stop of the "A"
group so that the cutting-off tool _R_ in front can be used for rounding
the corner _b_, Fig. 22. The stop lever _L_ is then shifted and the
turret is moved to a second stop of the "B" group. The corner _c_ is
then rounded and the shell is scored at _d_ by two inverted tools _S_
and _T_ at the rear, after which the finished work is severed by the
cut-off tool at the front. The cross-movement of these three tools is
controlled by positive stops on the cross-slide, and the latter is moved
to and fro by hand lever _O_. After the shell is cut off, the stop _M_,
mounted on the turret, Fig. 26, is swung into position, and the tube is
automatically fed forward to the swinging stop by the roll feed, as soon
as the chuck is released by operating lever _Q_. This completes the
cycle of operations. A copious supply of lubricant is, of course,
furnished to the tools during these operations, and the two boring-tool
shanks are hollow so that lubricant can be forced through them and be
made to play directly upon the cutters.
=Chuck Work in Flat Turret Lathe.=--Two examples of chuck work on the
Acme combination flat turret lathe are shown in Figs. 28 and 29. Fig. 28
shows the tool equipment for turning a cylindrical part _A_ which is
held in a three-jaw universal chuck. The front flange is first
rough-turned by a bent turning tool _B_. The diameter is regulated by
one of the cross-stops at _D_ which has been previously set and controls
the movement of the turret cross-slide. The longitudinal feed is
disengaged when the flange has been turned, by an independent stop. This
machine has twelve longitudinal stops, there being one for each turret
face and six auxiliary stops, in addition to the stops for the
cross-slide.
[Illustration: Fig. 28. Tool Equipment for Turning Scroll Gear Blank on
Acme Flat Turret Lathe]
After roughing the flange, the turret carriage is locked or clamped
rigidly to the bed to prevent any lengthwise movement, and the back face
of the front flange is rough-turned by tool _B_ in to the diameter of
the hub which is indicated by a micrometer dial on the cross-feed screw.
The carriage is then unlocked and auxiliary stop No. 7 is engaged (by
turning a knob at the front of the slide) and the cylindrical hub is
turned back to the rear flange, the feed being disengaged by the
auxiliary stop just as the tool reaches the flange. The cross-slide is
now moved outward, longitudinal auxiliary stop No. 8 is engaged, the
turret slide is moved against the stop, the carriage is locked and the
front sides of both the front and rear flanges are rough-faced by tools
_B_ and _C_. The turret is next indexed and the hole rough-bored by
cutter _E_. After again indexing the turret, the hub and flanges are
finish-turned and faced by tools _F_ and _G_, as described for the
rough-turning operation. The final operation is that of finishing the
bore by cutter _H_.
[Illustration: Fig. 29. Acme Flat Turret Lathe Arranged for Turning
Roller Feed Body]
The operation shown in Fig. 29 is that of turning the body of a roller
feed mechanism for a turret lathe. The casting is held in a three-jaw
universal chuck and it is first rough-bored by tool _A_. The turret is
then indexed and the side of the body and end of the hub are rough-faced
by tools at _B_. The turret is again indexed for rough-turning the
outside of the hub and body, by tools _C_ and _D_. Similar tools _E_
and _F_ are then used to finish these same surfaces, after which the end
of the hub and side of the body are finished by tools _G_ and _H_
similar to those located at _B_. The final operation is that of
finishing the bore by tool _J_ and cutting a groove in the outside of
the hub by the bent tool _K_.
[Illustration: Fig. 30. Turret and Head of Jones & Lamson Double-spindle
Flat Turret Lathe]
=Double-spindle Flat Turret Lathe.=--The extent to which modern turning
machines have been developed, especially for turning duplicate parts in
quantity, is illustrated by the design of turret lathe the turret and
head of which is shown in Fig. 30. This machine has two spindles and a
large flat turret which holds a double set of tools, so that two
duplicate castings or forgings can be turned at the same time. It was
designed primarily for chuck work and can be used as a single-spindle
machine if desirable. When two spindles are employed for machining two
duplicate parts simultaneously, considerably more time is required for
setting up the machine than is necessary for the regular single-spindle
type, but it is claimed that the increased rate of production obtained
with the two-spindle design more than offsets this initial handicap.
The manufacturers consider the single-spindle machine the best type for
ordinary machine building operations, regardless of whether the work is
turned from the bar or is of the chucking variety. On the other hand,
the double-spindle type is preferred when work is to be produced in such
quantities that the time for setting up the machine becomes a secondary
consideration.
[Illustration: Fig. 31. Diagram showing Tool Equipment and Successive
Steps in Machining Sprocket Blanks on Double-spindle Flat Turret Lathe]
When the double-spindle machine is used as a single-spindle type, a
chuck 17 inches in diameter is used, and when both spindles are in
operation, two 9-inch chucks are employed. The general outline of the
turret is square, and the tools are rigidly held, with a minimum amount
of overhang, by means of tool-blocks and binding screws connected with
the clamping plates. Two duplicate sets of tools are clamped to each
side of the turret and these operate simultaneously on the two pieces
held in the chucks or on faceplates. Primarily the turret is used in
but four positions, but when a 17-inch chuck or faceplate is employed,
corner blocks may be held by the clamping plates in which tools are
supported, giving, if necessary, four additional operations by indexing
the turret to eight positions.
A typical job to demonstrate the application of the double-spindle flat
turret lathe is illustrated in Fig. 31. The parts to be turned are
sprocket wheels which are held in the two 9-inch chucks. At the first
position of the turret (which is the one illustrated), the inside is
rough-bored by tools _A_. At the second position of the turret, tools
_B_ rough-face the inner sides of the flanges; tools _C_ face the outer
sides of the flanges, while tools _D_ turn the faces of the flanges. At
the third position of the turret, tools _E_ finish-turn the inside of
the flanges; tools _F_ finish-turn the outside of the flanges, while
tools _G_ finish the faces of the flanges. At the fourth position of the
turret, tools _H_ finish-bore the sprockets; tools _I_ complete the
turning on the outside of the flanges, while tools _J_ accurately size
the interior of the flanges.
With the double-spindle flat turret lathe, each operation is a double
operation, and the speeds are varied according to the nature of the cut;
thus, if at one position of the turret, the tools are required to rough
out the work, this may be done rapidly, for it has no bearing on the
other operations that are subsequently performed. Furthermore, if the
following operation has to be performed with great care, this may be
done without reducing the speed of the less exacting operations.
[Illustration: Fig. 32. Potter & Johnston Automatic Chucking and Turning
Machine]
=Automatic Chucking and Turning Machine.=--The chucking and turning
machine shown in Fig. 32 is automatic in its operation, the feeding of
the tools, indexing of the turret, etc., being done automatically after
the machine is properly arranged, and the work is placed in the chuck.
This machine is adapted to turning and boring a great variety of
castings, forgings or parts from bar stock, and it is often used in
preference to the hand-operated turret lathe, especially when a great
many duplicate parts are required. It is provided with mechanism for
operating the cross-slide, feeding the turret slide forward, returning
it rapidly, rotating the turret to a new position, and feeding it
forward quickly for taking a new cut. The cross-slide and turret-slide
movements are effected by cams mounted on the large drum _E_ seen
beneath the turret, while the various speed and feed changes are
effected by dogs and pins carried on disk _D_ which is keyed to the same
shaft that the cam drum is mounted upon. This shaft with the cam drum
and governing disk _D_, makes one revolution for each piece of work
completed. The cams for operating the turret slide are mounted upon the
periphery of drum _E_. The roll which engages the angular faces of these
cams and imparts movement to the turret is carried by an intermediate
slide which has rack teeth engaging a pinion on the square shaft _C_. By
turning this shaft with a crank, the position of the turret-slide, with
relation to the cam, may be adjusted for long or short work and long or
short tools, as may be required.
[Illustration: Fig. 33. Rear View of Machine showing the Cross-slide
Mechanism, Driving Gearing, etc.]
The cams which operate the cross-slide are mounted on the right-hand end
of drum _E_ and actuate the yoke _A_ (see Fig. 33) which extends
diagonally upward. The rear end of this yoke has rack teeth meshing with
the teeth of a segmental pinion, which is fastened to rock-shaft _B_.
At the headstock end, this rock-shaft carries another segmental pinion
meshing with rack teeth formed on the cross-slide. The movement imparted
to the yoke by the cams is thus transmitted through the pinions and
rock-shaft to the cross-slide.
[Illustration: Fig. 34. The Automatic Controlling Mechanism for Feeds
and Speeds]
The cam drum _E_ is driven by a pinion meshing with a gear attached to
its front side. This pinion is driven through a train of gearing from
pulley _L_ (see Fig. 34) which is belted to the spindle. The feeds are
thus always dependent on the spindle speed. By means of epicyclic
gearing and suitable clutches, the motion thus derived from the spindle
may be made rapid for returning the turret to be indexed and then
advancing it to the cutting position again, or very slow for the forward
feed when the tools are at work. These changes from slow to fast or
_vice versa_ are controlled by disk _D_. This disk carries pins which
strike a star wheel located back of the disk at the top, and as this
star wheel is turned, the speeds are changed by operation of the gearing
and clutches referred to. The first pin _M_ that strikes the star wheel
advances it one-sixth of a rotation, changing the feed from fast to
slow; the next pin that strikes it advances it another sixth of a
rotation, changing the feed from slow to fast and so on. By adjusting
the pins for each piece of work, the feed changes are made to take place
at the proper time. Handwheel _E_ is geared with the cam-shaft on which
the star wheel is mounted, so that the feeds may be changed by hand if
desired.
In addition to these feed-changing pins, disk _D_ has a dog which
operates a lever by which the feed movement is stopped when the work has
been completed. Four rates of feed are provided by quick change gearing
of the sliding gear type, operated by handle _K_. With this handle set
in the central position, the feed is disengaged. On the periphery of
disk _D_ are also clamped dogs or cams _N_, which operate a horizontal
swinging lever _P_ connected by a link with vertical lever _J_, which
controls the two spindle speeds with which the machine is provided.
Either one of these speeds can be automatically engaged at any time, by
adjusting the cams _N_ on disk _D_.
Lever _H_ connects or disconnects the driving pulley from the shaft on
which it is mounted, thus starting or stopping the machine. The square
shaft _G_ serves to operate the drums by hand and is turned with a
crank. The rotation of the turret, which takes place at the rear of its
travel, is, of course, effected automatically. A dog, which may be seen
in Fig. 32 at the side of the bed, is set to trip the turret revolving
mechanism at the proper point in the travel, to avoid interference
between the tools and the work. The turret is provided with an automatic
clamping device. The mechanism first withdraws the locking pin, unclamps
the turret, revolves it, then throws in the locking pin and clamps the
turret again.
=Example of Work on Automatic Turning Machine.=--The piece selected for
illustrating the "setting up" and operation of the automatic chucking
and turning machine is shown in Fig. 35. This is a second operation, and
a very simple one which will clearly illustrate the principles involved.
In the first operation, the hole was drilled, bored and reamed, the
small end of the bushing faced, and the outside diameter finished, as
indicated by the sketch to the left. (The enlarged diameter at the end
was used for holding the work in the chuck.) In the second operation
(illustrated to the right), the enlarged chucking end is cut off and, in
order to prevent wasting this piece, it is made into a collar for
another part of the machine for which the bushing is intended; hence,
the outside diameter is turned and the outside end faced, before cutting
off the collar. In addition, the bushing is recessed in the second
operation, and the outer end faced. In order to have the surfaces
finished in the second operation, concentric with those machined in the
first operation, the chuck is equipped with a set of soft "false jaws"
which have been carefully bored to exactly the diameter of the work to
be held.
[Illustration: Fig. 35. Simple Example of Work done in Automatic
Chucking and Turning Machine]
The first thing to determine when setting up a machine of this type is
the order of operations. In this particular case, the order is as
follows: At the first position of the turret, the outside collar is
rough-turned and the outer end rough-faced. At the second position, the
collar is turned to the required diameter and the outer face is
finished. The third face of the turret is not equipped with tools, this
part of the cycle being taken up in cutting off the collar with a
cut-off tool on the rear cross-slide. The fourth operation is that of
recessing the bushing, and the fifth operation, facing the end to remove
the rough surface left by the cutting-off tool.
The tools _A_ and _B_, Fig. 36, used for turning the outside of the
flange, are held in brackets _C_ bolted to the face of the turret.
These brackets are each provided with three holes for carrying turning
tool-holders. This arrangement provides for turning a number of
diameters at different positions, simultaneously, but for this
particular operation, a single cutting tool for each tool-holder is all
that is necessary. A special device is used for recessing and will be
described later.
[Illustration: Fig. 36. Front View of Machine set up for the Finishing
Operation on the Recessed Bushing and Collar shown in the Foreground and
in Fig. 35]
=Determining Speed and Feed Changes.=--As previously mentioned, the
particular machine illustrated in Fig. 32 can be arranged for two
automatic changes of speed to suit different diameters on the work. The
change gears that will give the required spindle speeds should first be
selected. These change gears for different speeds are listed on a speed
and feed plate attached to the headstock of the machine (see Fig. 37).
It is possible to use one speed from the list given for the fast train
of gears, and one from the list for the slow train, so long as the same
gears are not used in each case. The diameter of the collar on the work
shown in Fig. 35 is 2-1/2 inches, and the diameter of the body is 2
inches. Assuming that the surface speed for this job should be about 40
feet per minute, a little calculation shows that the 66 revolutions per
minute, given by the fast train of gears, is equivalent to a surface
speed of 43 feet per minute on a diameter of 2-1/2 inches. Moreover, the
78 revolutions per minute obtained from the slow train of gearing, gives
about 41 feet per minute on a diameter of 2 inches. The spindle gearing
indicated for these speeds is, therefore, placed in position on the
proper studs at the back of the machine.
[Illustration: Fig. 37. Plate on the Headstock of Machine Illustrated in
Fig. 32 giving the Speeds and Feeds]
Next we have to determine on which faces of the turret to place the
different tools. Each turret face is numbered to agree with the
corresponding feed cam on the drum. The speed and feed plate (Fig. 37)
gives the various feeds obtainable per revolution of the spindle. As
will be seen, the different cams give different feeds. Cam No. 1 has a
coarse feed suitable for roughing; cam No. 2 a finer feed adapted to
finishing, and so on. Since the first operation consists in
rough-turning, cam No. 1 is used. Cam No. 2, which gives a finer feed,
is used for the finish-turning operation. Cam No. 4, which is ordinarily
used for reaming, could, in this case, be used for recessing, as this
recess is for clearance only and may be bored with a coarse feed.
The final operation, which is that of facing, can be done with any cam
and cam No. 5 may be used. It will be understood that for facing
operations, the feeds given do not apply. As the roll passes over the
point of the feed cam at the extreme end of the movement, the feed of
the turret slide is gradually slowed down to zero; since the facing
takes place in the last eighth or sixteenth inch of this movement, it is
done at a feed which is gradually reduced to zero. This is, of course,
as it should be, and it is not necessary to pay any attention to the
tabulated feeds in facing operations.
=Setting the Turret Slide.=--The next adjustment is that of setting the
turret slide. In making this adjustment the turret is set in such
relation to the work that the tools will have but a small amount of
overhang, the cam-shaft being revolved by hand until the cam-roll is at
the extreme top of the forward feeding cam, so that the turret slide is
at the extreme of its forward movement. When this adjustment has been
made by the means provided, set the turret index tripping dog so as to
revolve the turret at the proper point. After a turning tool-holder and
tool is attached to the face of the turret, cam No. 1 is placed in its
operating position and is revolved by hand until the roll is on the
point of the cam and the turret at the forward extreme of its motion. At
this point the tool-holder is set so that the cutter will be far enough
forward to complete its turning operation. The feed cam is then turned
backward, thus returning the turret slide, and the cutter is set to turn
the flange to the proper diameter for the roughing cut. The turret slide
is fed forward and back while the cutter is adjusted, and when it is
properly set, the flange is turned, the cam-drum being fed by hand. This
is the first trial cut on the piece.
A facing tool, shown in the working position in Fig. 36, is placed at
this station of the turret, being held in the turret hole. This tool has
a pilot bar and a holder which contains a facing blade. Feeding by hand,
as before, the tool is adjusted lengthwise so as to rough-face the work
to the dimension desired. In a similar way the finish-turning and
facing tools for the second position of the turret are set, the
cam-shaft being revolved by hand to bring this second face and second
cam into the working position. (The finish-facing tool is not shown in
place in Fig. 36.)
[Illustration: Fig. 38. Diagram of Cross-slide Cams and Feeding
Mechanism]
=Setting the Cross-slide Cam.=--As previously mentioned, the third
turret face has no tool, the cutting off of the collar being done during
this part of the cycle of operations. It has been taken for granted that
in setting the turret slide, room has been left between it and the chuck
for the cross-slide. The cross-slide is clamped in a longitudinal
position on the bed, convenient for the cutting-off operation, which is
done with a tool _D_ (Fig. 36) in the rear toolpost, thus leaving the
front unobstructed for the operator. When both forming and cutting off
are to be done, the forming tool is generally held at the front and the
cutting-off tool at the back because heavier and more accurate forming
can be done with the work revolving downward toward a tool in the front
toolpost, than with the tool at the rear where it is subjected to a
lifting action.
The arrangement of the cross-slide cams is shown in Fig. 38, which is an
end view of the large drum _E_, Fig. 32. The rear feed cam is the one to
be used, and since this cutting-off operation is a short one, it may be
done during the return of the turret for position No. 3. The cam drum
is, therefore, rotated by hand until the turret face No. 3 has begun to
return. The cross-slide cams are then loosened and the rear feed cam is
swung around to just touch the roller _R_ which operates arm _A_, the
cross-slide having been adjusted out to nearly the limit of its forward
travel, leaving approximately enough movement for cutting off the
collar. The rear feed cam is then clamped in this position.
A cutting-off tool is next placed in the rear toolpost at the proper
height. The rear toolpost slide is then adjusted to bring the point of
the cutting-off tool up to the work, and the cam drum is revolved by
hand until the piece is cut off. The cross-slide tool is, of course, set
in the proper position to make a collar of the required thickness.
Feeding by hand is discontinued when the roll is on the point of the
cam; the cutting-off tool slide is then permanently set on the
cross-slide so that the point of the cutting-off tool enters the bore
just far enough to completely sever the collar from the bushing. The
motion of the cam drum is continued, by hand, until the roll is over the
point of the feed cam. The cross-slide is then pushed back, by hand,
until the cam and roll are again in contact, when the return cam is
brought up and clamped in position, so that there is just room for the
roll between the feed cam and the return cam. The rear return cam (as
the hand feed of the cam drum is continued) brings the cross-slide back
to its central position. Since there is no front tool used for this
series of operations (although a tool is shown in the front toolpost,
Fig. 36), the first feed and return cams are allowed to remain wherever
they happen to be. These cam adjustments can all be made from the front
of the machine.
=Setting the Boring Tool for Recessing.=--The feeding of the turret
slide is now continued to make sure that the cutting-off tool is
returned to its normal position before the facing tool in the next face
of the turret begins to work. The facing of the bushing, so far as the
setting of the tool is concerned, is merely a repetition of the facing
operation at the first position of the turret. The recessing tool is
next set. This tool, which is shown diagrammatically in Fig. 39, is very
simple as compared with the somewhat complex operation it has to
perform. This recess is for clearance only, and accurate dimensions and
fine finish are not necessary. The recessing tool consists simply of a
slender boring-bar held in the turret and carrying a cutter suitably
located about midway the bar. The forward end of the bar is small enough
to enter a bell-mouthed bushing held in the chuck. The boring-bar is
bent to one side far enough so that the cutter clears the hole as the
bar enters, but is forced into the work as the rounded hole of the
bushing engages the end of the bar and deflects it into the working
position. The upper diagram shows the position of the bar as it enters
the hole, and the lower one the position after it has entered the
bushing and is engaged in turning the recess. This bar is set in the
turret so that at the extreme forward travel of the turret slide, the
recess will be bored to the required length. The cutter must also be
adjusted to bore to the desired diameter. This completes the setting of
the cutting tools.
[Illustration: Fig. 39. Flexible Boring Tool used for Recessing a
Bushing in Automatic Chucking and Turning Machine]
=Adjustments for Automatic Feed and Speed Changes.=--The machine must
now be set to perform automatically the desired changes of spindle speed
and the fast and slow cam movements for the tools. After placing a new
piece of work in the machine (the first one having been completed in the
setting-up operation), the cam-shaft is revolved by hand until the
turning tool in turret face No. 1 is just about to begin its cut. The
control wheel _D_, Fig. 34, is rotated in its normal direction until the
next graduation marked "slow" is in line with an index mark on the base
of the machine. Then the nearest pin _M_ is moved up until it bears
against a tooth of the star wheel (previously referred to) and is
clamped in this position. The pin should now be in the proper location,
but to test its position, rotate the cam shaft backward by hand and
throw in the automatic feed; then watch the cut to see if the drum slows
down just before the tool begins to work. If it does not, the pin should
be adjusted a little, one way or the other, as may be required. (In
going over a piece of work for the first time, it is best to have the
feed set to the smallest rate, feed change handle _K_ being in position
No. 1.)
After the cut has been completed and the turret feed cam-roll is on the
high part of the cam, the power feed should again be stopped and the
handwheel revolved until the next graduation marked "fast" is opposite
the index mark. The next stop pin is then moved up until it just touches
the star wheel, where it is clamped in position. The feed being again
thrown in, the turret will be returned rapidly, indexed, and moved
forward for the second operation. After stopping the automatic movement,
the pins are set for this face, and so on for all the operations,
including that in which the cross-slide is used for cutting off the
finished collar.
As the first, second, and third operations are on comparatively large
diameters, they should be done at the slow speed, handle _J_, Fig. 34,
being set to give that speed. While the turret slide is being returned
between operations 3 and 4, one of the spindle speed-changing dogs _N_
should be clamped to the rim of disk _D_ so as to change the spindle
speed to the fast movement. This speed is continued until the last
operation is completed, when a second dog is clamped in place to again
throw in the slow movement. The feed knock-off dog should also be
clamped in place on the disk to stop the machine at the completion of
the fifth operation, when the turret is in its rear position. This
completes the setting up of the machine. If the feed is finer than is
necessary, the feed change handle _K_ may now be moved to a position
which will give the maximum feed that can be used.
It has taken considerable time to describe the setting up of the machine
for this simple operation, but in the hands of a competent man it can be
done quite rapidly. While a simple operation has been referred to in the
foregoing, it will be understood that a great variety of work can be
done on a machine of this type. It is not unusual to see as many as ten
cutting tools operating simultaneously on a piece of work, the tools
being carried by the turret, cross-slide and back facing attachment. The
latter is operated from a separate cam applied to the cam-shaft and
acting through levers on a back facing bar which passes through a hole
in the spindle. In this back facing bar may be mounted drills, cutters,
facing tools, etc. for machining the rear face of a casting held in the
chuck jaws. Where extreme accuracy is required, a double back facing
attachment may be used, arranged with cutters for taking both roughing
and finishing cuts. The use of this attachment often saves a second
operation. This automatic chucking and turning machine is also adapted
for bar work, especially in diameters varying from 3 to 6 inches.
=Turning Flywheel in Automatic Chucking and Turning Machine.=--A typical
operation on the Potter & Johnston automatic chucking and turning
machine is illustrated in Fig. 40, which shows the machine arranged for
turning the cast-iron flywheel for the engine of a motor truck. The rim
is turned and faced on both sides and the hub is bored, reamed and faced
on both sides. The flywheel casting is held in a chuck by three special
jaws which grip the inside of the rim. The order of the operations is as
follows:
The rear end of the hub is faced by the back facing bar; the cored hole
is started by a four-lipped drill in the turret and the front end of the
hub is rough-faced. (These tools are on the rear side of the turret
when the latter is in the position shown in the illustration.) After the
turret indexes, the hole is rough-bored by tool _A_ and while this is
being done, the outside of the rim is rough-turned by tool _B_ held in a
special bracket attached to the turret. Both sides of the rim are also
rough-faced by tools _C_ and _D_ held at the front of the cross-slide,
this operation taking place at the same time that the rim is turned and
the hole is being bored.
[Illustration: Fig. 40. Machining Flywheels in Potter & Johnston
Automatic Chucking and Turning Machine]
The turret again automatically recedes and indexes, thus locating bar
_E_ and turning tool _G_ in the working position. The hole is then
finish-bored by tool _E_ and the hub is finish-faced by blade _F_; at
the same time the rim is finish-turned by tool _G_ and the sides are
finish-faced to the proper width by two tools held at the rear of the
cross-slide. The turret automatically recedes and indexes a third time,
thus locating the flat-cutter reamer-bar _H_ in the working position and
then the hole is reamed to the required diameter. This completes the
cycle of operations. The total time for machining this flywheel is forty
minutes.
=Automatic Multiple-spindle Chucking Machine.=--An example of the
specialized machines now used for producing duplicate parts, is shown in
Fig. 41. This is a "New Britain" automatic multiple-spindle chucking
machine of the single-head type and it is especially adapted for boring,
reaming and facing operations on castings or forgings which can readily
be held in chuck jaws. This particular machine has five spindles, which
carry and revolve the tools. The work being machined is held stationary
in the multiple chuck turret _A_ which holds each part in line with one
of the spindles and automatically indexes, so that the work passes from
one spindle to another until it is finished. The turret then indexes the
finished piece to a sixth or "loading position" which is not opposite a
spindle, where the part is removed and replaced with a rough casting.
Each pair of chuck jaws is operated independently of the others by the
use of a chuck wrench. These jaws are made to suit the shape of the
work.
[Illustration: Fig. 41. New Britain Multiple-spindle Automatic Chucking
Machine of Single-head Type]
When a single-head machine is in operation, the turret advances and
feeds the work against the revolving tools so that a number of pieces
are operated upon at the same time. The turret is fed by a cam drum _B_.
Cam strips are bolted to the outside of this drum and act directly
against a roller attached to the yoke _C_ which can be clamped in
different positions on the spindle _D_, the position depending upon the
length of the work. On the opposite end of the turret spindle is the
indexing mechanism _E_. An automatically spring-operated latch _F_
engages notches in the rim of the dividing wheel, thus accurately
locating the turret. The turret is locked by a steadyrest _G_, which,
for each working position, automatically slides into engagement with one
of the notches in the turret. This relieves the indexing mechanism of
all strain.
[Illustration: Fig. 42. Detail View of New Britain Double-head
Eight-spindle Machine, Boring, Reaming and Facing Castings]
This type of machine is also built with two spindle heads, the
double-head design being used for work requiring operations on both
ends. When the double-head machine is in operation, the revolving
spindles and tools advance on both sides of the chuck turret, the latter
remaining stationary except when indexing. The feed drums on the
double-head machine are located directly beneath each group of spindles.
Fig. 42 shows an example of work on a machine of the double-head design.
This is an eight-spindle machine, there being two groups of four
spindles on each side of the turret. The castings _E_ are for the wheel
hubs of automobiles. The order of the operations on one of the castings,
as it indexes around, is as follows: The hole in the hub is first
rough-reamed by taper reamer _A_ and the opposite end of the hub is
rough-faced and counterbored by a tool in spindle _A_{1}_. When the
turret indexes, this same casting is reamed close to the finished size
by reamer _B_ and the left end of the hub is rough-faced by cutter _F_,
while a tool in the opposite spindle _B_{1}_ finishes the counterboring
and facing operation. At the third position, reamer _C_ finishes the
hole accurately to size, and when the work is indexed to the fourth
position, the hub on the left side is finish-faced by a tool in spindle
_D_. (The third and fourth spindles of the right-hand group are not used
for this particular operation.) When the turret again indexes, the
finished casting is removed and replaced with a rough one. While the
successive operations on a single casting have just been described, it
will be understood that all of the tools operate simultaneously and that
a finished casting arrives at the unloading and loading position each
time the turret indexes. Three hundred of these malleable castings are
machined in nine hours.
=Selecting Type of Turning Machine.=--The variety of machine tools now
in use is very extensive, and as different types can often be employed
for the same kind of work, the selection of the best and most efficient
machine is often a rather difficult problem. To illustrate, there are
many different types and designs of turning machines, such as the
ordinary engine lathe, the hand-operated turret lathe, the
semi-automatic turning machine, and the fully automatic type, which,
after it is "set up" and started, is entirely independent. Hence, when a
certain part must be turned, the question is, what kind of machine
should be used, assuming that it would be possible to employ several
different machines? The answer to this question usually depends
principally upon the number of parts that must be turned.
For example, a certain casting or forging might be turned in a lathe,
which could be finished in some form of automatic or semi-automatic
turning machine much more quickly. It does not necessarily follow,
however, that the automatic is the best machine to use, because the
lathe is designed for general work and the part referred to could
doubtless be turned with the regular lathe equipment, whereas the
automatic machine would require special tools and it would also need to
be carefully adjusted. Therefore, if only a few parts were needed, the
lathe might be the best tool to use, but if a large number were
required, the automatic or semi-automatic machine would doubtless be
preferable, because the saving in time effected by the latter type would
more than offset the extra expense for tool equipment and setting the
machine. It is also necessary, in connection with some work, to consider
the degree of accuracy required, as well as the rate of production, and
it is because of these varying conditions that work of the same general
class is often done in machines of different types, in order to secure
the most efficient results.
CHAPTER VI
VERTICAL BORING MILL PRACTICE
All the different types of turning machines now in use originated from
the lathe. Many of these tools, however, do not resemble the lathe
because, in the process of evolution, there have been many changes made
in order to develop turning machines for handling certain classes of
work to the best advantage. The machine illustrated in Fig. 1 belongs to
the lathe family and is known as a vertical boring and turning mill.
This type, as the name implies, is used for boring and turning
operations, and it is very efficient for work within its range. The part
to be machined is held to the table _B_ either by clamps or in chuck
jaws attached to the table. When the machine is in operation, the table
revolves and the turning or boring tools (which are held in tool-blocks
_T_) remain stationary, except for the feeding movement. Very often more
than one tool is used at a time, as will be shown later by examples of
vertical boring mill work. The tool-blocks _T_ are inserted in tool-bars
_T_{1}_ carried by saddles _S_ which are mounted on cross-rail _C_. Each
tool-head (consisting of a saddle and tool-bar) can be moved
horizontally along cross-rail _C_, and the tool-bars _T_{1}_ have a
vertical movement. These movements can be effected either by hand or
power.
When a surface is being turned parallel to the work table, the entire
tool-head moves horizontally along the cross-rail, but when a
cylindrical surface is being turned, the tool-bar moves vertically. The
tool-heads are moved horizontally by the screws _H_ and _H_{1}_, and the
vertical feed for the tool-bars is obtained from the splined shafts _V_
and _V_{1}_, there being a separate screw and shaft for each head so
that the feeding movements are independent. These feed shafts are
rotated for the power feed by vertical shafts _A_ and _A_{1}_ on each
side of the machine.
These vertical shafts connect with the feed shafts through bevel and
spur gears located at the ends of the cross-rail. On most boring mills,
connection is made with one of the splined shafts _V_ or screw _H_, by a
movable gear, which is placed on whichever shaft will give the desired
direction of feed. The particular machine illustrated is so arranged
that either the right or left screw or feed shaft can be engaged by
simply shifting levers _D_{1}_ or _D_.
[Illustration: Fig. 1. Gisholt Vertical Boring and Turning Mill]
The amount of feed per revolution of the table is varied for each
tool-head by feed-changing mechanisms _F_ on each side of the machine.
These feed boxes contain gears of different sizes, and by changing the
combinations of these gears, the amount of feed is varied. Five feed
changes are obtained on this machine by shifting lever _E_, and this
number is doubled by shifting lever _G_. By having two feed boxes, the
feeding movement of each head can be varied independently. The direction
of either the horizontal or vertical feed can be reversed by lever _R_,
which is also used for engaging or disengaging the feeds. This machine
is equipped with the dials _I_ and _I_{1}_ which can be set to
automatically disengage the feed at any predetermined point. There are
also micrometer dials graduated to thousandths of an inch and used for
adjusting the tools without the use of measuring instruments.
The work table _B_ is driven indirectly from a belt pulley at the rear,
which transmits the power through gearing. The speed of the table can be
varied for turning large or small parts, by levers _J_ and _K_ and the
table can be started, stopped or rotated part of a revolution by lever
_L_ which connects with a friction clutch. There are corresponding feed
and speed levers on the opposite side, so that the machine can be
controlled from either position.
The heads can be adjusted along the cross-rail for setting the tools by
hand-cranks _N_, and the tool slides can be moved vertically by turning
shafts _V_ with the same cranks. With this machine, however, these
adjustments do not have to be made by hand, ordinarily, as there are
rapid power movements controlled by levers _M_. These levers
automatically disengage the feeds and enable the tool-heads to be
rapidly shifted to the required position, the direction of the movement
depending upon the position of the feed reverse lever _R_ and lever _D_.
This rapid traverse, which is a feature applied to modern boring mills
of medium and large size, saves time and the labor connected with hand
adjustments. The cross-rail _C_ has a vertical adjustment on the faces
of the right and left housings which support it, in order to locate the
tool-heads at the right height for the work. This adjustment is effected
by power and is controlled by levers at the sides of the housings.
Normally, the cross-rail is bolted to the housings, and these bolts must
be loosened before making the adjustment, and must always be tightened
afterwards.
The function of these different levers has been explained to show, in a
general way, how a vertical boring machine is operated. It should be
understood, however, that the arrangement differs considerably on
machines of other makes. The construction also varies considerably on
machines of the same make but of different size.
[Illustration: Fig. 2. Small Boring and Turning Mill with Single
Turret-head]
All modern vertical boring mills of medium and large sizes are equipped
with two tool-heads, as shown in Fig. 1, because a great deal of work
done on a machine of this type can have two surfaces machined
simultaneously. On the other hand, small mills of the type illustrated
in Fig. 2 have a single head. The toolslide of this machine, instead of
having a single tool-block, carries a five-sided turret _T_ in which
different tools can be mounted. These tools are shifted to the working
position as they are needed, by loosening binder lever _L_ and turning
or "indexing" the turret. The turret is located and locked in any of its
five positions by lever _I_, which controls a plunger that engages
notches at the rear. Frequently, all the tools for machining a part can
be held in the turret, so that little time is required for changing from
one tool to the next. Some large machines having two tool-heads are also
equipped with a turret on one head.
=Boring and Turning in a Vertical Boring Mill.=--The vertical boring
mill is, in many respects, like a lathe placed in a vertical position,
the table of the mill corresponding to the faceplate or chuck of the
lathe and the tool-head to the lathe carriage. Much of the work done by
a vertical mill could also be machined in a lathe, but the former is
much more efficient for work within its range. To begin with, it is more
convenient to clamp work to a horizontal table than to the vertical
surface of a lathe faceplate, or, as someone has aptly said, "It is
easier to lay a piece down than to hang it up." This is especially true
of the heavy parts for which the boring mill is principally used. Very
deep roughing cuts can also be taken with a vertical mill. This type of
machine mill is designed for turning and boring work which, generally
speaking, is quite large in diameter in proportion to the width or
height. The work varies greatly, especially in regard to its diameter,
so that boring mills are built in a large range of sizes. The small and
medium sizes will swing work varying from about 30 inches to 6 or 7 feet
in diameter, whereas large machines, such as are used for turning very
large flywheels, sheaves, etc., have a swing of 16 or 20 feet, and
larger sizes are used in some shops. The size of a vertical mill, like
any other machine tool, should be somewhat in proportion to the size of
the work for which it is intended, as a very large machine is unwieldy,
and, therefore, inefficient for machining comparatively small parts.
=Holding and Setting Work on Boring Mill Table.=--There are three
general methods of holding work to the table of a boring mill; namely,
by the use of chucks, by ordinary bolts and clamps, or in special
fixtures. Chucks which are built into the table (as illustrated in Fig.
2) and have both universal and independent adjustments for the jaws can
be used to advantage for holding castings that are either round or
irregular in shape. The universal adjustment is used for cylindrical
parts, such as disks, flywheels, gear blanks, etc., and the independent
adjustment, for castings of irregular shape. Chucks which have either an
independent or universal movement for the jaws are known as a
"combination" type and usually have three jaws. There is also a four-jaw
type which has the independent adjustment only. This style is preferable
for work that is not cylindrical and which must be held very securely.
Chuck jaws that do not form a part of the machine table, but are bolted
to it in the required position, are also employed extensively,
especially on comparatively large machines.
Most of the work done in a vertical mill is held in a chuck.
Occasionally, however, it is preferable to clamp a part directly to the
table. This may be desirable because of the shape and size of the work,
or because it is necessary to hold a previously machined surface
directly against the table in order to secure greater accuracy.
Sometimes a casting is held in the chuck for turning one side, and then
the finished side is clamped against the table for turning the opposite
side. Parts which are to be machined in large quantities are often held
in special fixtures. This method is employed when it enables the work to
be set up more quickly than would be possible if regular clamps or chuck
jaws were used.
Work that is to be turned or bored should first be set so that the part
to be machined is about central with the table. For example, the rim of
a flywheel should be set to run true so that it can be finished by
removing about the same amount of metal around the entire rim; in other
words, the rim should be set concentric with the table, as shown in Fig.
3, and the sides of the rim should also be parallel to the table.
[Illustration: Fig. 3. Plan View showing Flywheel Casting Chucked for
Turning]
A simple tool that is very useful for testing the position of any
cylindrical casting consists of a wooden shank into which is inserted a
piece of wire, having one end bent. This tool is clamped in the toolpost
and as the work revolves the wire is adjusted close to the cylindrical
surface being tested. The movement of the work with relation to the
stationary wire point will, of course, show whether or not the part runs
true. The advantage of using a piece of wire for testing, instead of a
rigid tool, is that the wire, owing to its flexibility, will simply be
bent backward if it is moved too close to a surface which is
considerably out of true. The upper surface of a casting can be tested
for parallelism with the table by using this same wire gage, or by
comparing the surface, as the table is revolved slowly, with a tool held
in the toolpost. An ordinary surface gage is also used for this purpose.
The proper surface to set true, in any case, depends upon the
requirements. A plain cylindrical disk would be set so that the outside
ran true and the top surface was parallel with the table. When setting a
flywheel, if the inside of the rim is to remain rough, the casting
should be set by this surface rather than by the outside, so that the
rim, when finished, will be uniform in thickness.
As far as possible, chucks should be used for holding cylindrical parts,
owing to their convenience. The jaws should be set against an interior
cylindrical surface whenever this is feasible. To illustrate, the
flywheel in Fig. 3 is gripped by the inside of the rim which permits the
outside to be turned at this setting of the work. It is also advisable
to set a flywheel casting in the chuck so that a spoke rests against one
of the jaws as at _d_, if this is possible. This jaw will then act as a
driver and prevent the casting from slipping or turning in the chuck
jaws, owing to the tangential pressure of the turning tool. When a cut
is being taken, the table and work rotate as shown by arrow _a_, and the
thrust of the cut (taken by tool _t_) tends to move the wheel backward
against the direction of rotation, as shown by arrow _b_. If one of the
chuck jaws bears against one of the spokes, this movement is prevented.
It is not always feasible to use a chuck jaw as a driver and then a
special driver having the form of a small angle-plate or block is
sometimes bolted directly to the table. Another method of driving is to
set a brace between a spoke or projection on the work and a chuck jaw or
strip attached to the table. Drivers are not only used when turning
flywheels, but in connection with any large casting, especially when
heavy cuts have to be taken. Of course, some castings are so shaped that
drivers cannot be employed.
=Turning in a Boring Mill.=--The vertical type of boring mill is used
more for turning cylindrical surfaces than for actual boring, although a
large part of the work requires both turning and boring. We shall first
consider, in a general way, how surfaces are turned and then refer to
some boring operations. The diagram _A_, Fig. 4, illustrates how a
horizontal surface would be turned. The tool _t_ is clamped in
tool-block _t_{1}_, in a vertical position, and it is fed horizontally
as the table and work rotate. The tool is first adjusted by hand for the
proper depth of cut and the automatic horizontal feed is then engaged.
When a cylindrical surface is to be turned, the tool (provided a
straight tool is used) is clamped in a horizontal position and is fed
downward as indicated at _B_. The amount that the tool should feed per
revolution of the work, depends upon the kind of material being turned,
the diameter of the turned part and the depth of the cut.
[Illustration: Fig. 4. (A) Turning a Flat Surface. (B) Turning a
Cylindrical Surface]
Most of the parts machined in a vertical boring mill are made of cast
iron and, ordinarily, at least one roughing and one finishing cut is
taken. The number of roughing cuts required in any case depends, of
course, upon the amount of metal to be removed. An ordinary roughing cut
in soft cast iron might vary in depth from 1/8 or 3/16 inch to 3/8 or
1/2 inch and the tool would probably have a feed per revolution of from
1/16 to 1/8 inch, although deeper cuts and coarser feeds are sometimes
taken. These figures are merely given to show, in a general way, what
cuts and feeds are practicable. The tool used for roughing usually has a
rounded end which leaves a ridged or rough surface. To obtain a smooth
finish, broad flat tools are used. The flat cutting edge is set parallel
to the tool's travel and a coarse feed is used in order to reduce the
time required for taking the cut. The finishing feeds for cast iron vary
from 1/4 to 3/4 inch on ordinary work. The different tools used on the
vertical mill will be referred to more in detail later.
All medium and large sized vertical boring mills are equipped with two
tool-heads and two tools are frequently used at the same time,
especially on large work. Fig. 9 illustrates the use of two tools
simultaneously. The casting shown is a flywheel, and the tool on the
right side turns the upper side of the rim, while the tool on the left
side turns the outside or cylindrical surface. As a boring mill table
rotates in a counter-clockwise direction, the left-hand tool is reversed
to bring the cutting edge at the rear. By turning two surfaces at once,
the total time for machining the casting is, of course, greatly reduced.
The turning of flywheels is a common vertical boring mill operation, and
this work will be referred to in detail later on.
[Illustration: Fig. 5. Tools for Boring and Reaming Holes]
=Boring Operations.=--There are several methods of machining holes when
using a vertical boring mill. Ordinarily, small holes are cored in
castings and it is simply necessary to finish the rough surface to the
required diameter. Some of the tools used for boring and finishing
comparatively small holes are shown in Fig. 5. Sketch _A_ shows a boring
tool consisting of a cutter _c_ inserted in a shank, which, in turn, is
held in the tool slide, or in a turret attached to the tool slide. With
a tool of this type, a hole is bored by taking one or more cuts down
through it. The tool shown at _B_ is a four-lipped drill which is used
for drilling cored holes preparatory to finishing by a cutter or reamer.
This drill would probably finish a hole to within about 1/32 inch of the
finish diameter, thus leaving a small amount of metal for the reamer to
remove. The tool illustrated at _C_ has a double-ended flat cutter _c_,
which cuts on both sides. These cutters are often made in sets for
boring duplicate parts. Ordinarily, there are two cutters in a set, one
being used for roughing and the other for finishing. The cutter passes
through a rectangular slot in the bar and this particular style is
centrally located by shoulders _s_, and is held by a taper pin _p_. Some
cutter bars have an extension end, or "pilot" as it is called, which
passes through a close-fitting bushing in the table to steady the bar.
Sketch _D_ shows a finishing reamer. This tool takes a very light cut
and is intended to finish holes that have been previously bored close to
the required size. Sometimes a flat cutter _C_ is used for roughing and
a reamer for finishing. The reamer is especially desirable for
interchangeable work, when all holes must have a smooth finish and be of
the same diameter. When a reamer is held rigidly to a turret or
toolslide, it is liable to produce a hole that is either tapering or
larger than the reamer diameter. To prevent this, the reamer should be
held in a "floating" holder which, by means of a slight adjustment,
allows the reamer to align itself with the hole. There are several
methods of securing this "floating" movement. (See "Floating Reamer
Holders.")
[Illustration: Fig. 6. Boring with Regular Turning Tools]
Large holes or interior cylindrical surfaces are bored by tools held in
the regular tool-head. The tool is sometimes clamped in a horizontal
position as shown at _A_, Fig. 6, or a bent type is used as at _B_. Cast
iron is usually finished by a broad flat tool as at _C_, the same as
when turning exterior surfaces. Obviously a hole that is bored in this
way must be large enough to admit the tool-block.
[Illustration: Fig. 7. Set of Boring Mill Tools]
=Turning Tools for the Vertical Boring Mill.=--A set of turning tools
for the vertical boring mill is shown in Fig. 7. These tools can be used
for a wide variety of ordinary turning operations. When a great many
duplicate parts are to be machined, special tool equipment can often be
used to advantage, but as the form of this equipment depends upon the
character of the work, only standard tools have been shown in this
illustration. The tool shown at _A_ is a right-hand, roughing tool, and
a left-hand tool of the same type is shown at _B_. Tool _C_ is an offset
or bent, left-hand round nose for roughing, and _D_ is a right-hand
offset roughing tool. A straight round nose is shown at _E_. Tool _F_
has a flat, broad cutting edge and is used for finishing. Left-and
right-hand finishing tools of the offset type are shown at _G_ and _H_,
respectively. Tool _I_ has a square end and is used for cutting grooves.
Right-and left-hand parting tools are shown at _J_ and _K_, and tool _L_
is a form frequently used for rounding corners.
[Illustration: Fig. 8. Diagrams Illustrating Use of Different Forms of
Tools]
The diagrams in Fig. 8 show, in a general way, how each of the tools
illustrated in Fig. 7 are used, and corresponding tools are marked by
the same reference letters in both of these illustrations. The right-and
left-hand roughing tools _A_ and _B_ are especially adapted for taking
deep roughing cuts. One feeds away from the center of the table, or to
the right (when held in the right-hand tool-block) and the other tool is
ground to feed in the opposite direction. Ordinarily, when turning plain
flat surfaces, the cut is started at the outside and the tool feeds
toward the center, as at _B_, although it is sometimes more convenient
to feed in the opposite direction, as at _A_, especially when there is a
rim or other projecting part at the outside edge. The tool shown at _A_
could also be used for turning cylindrical surfaces, by clamping it in a
horizontal position across the bottom of the tool-block. The feeding
movement would then be downward or at right-angles to the work table.
The offset round-nose tools _C_ and _D_ are for turning exterior or
interior cylinder surfaces. The shank of this tool is clamped in the
tool-block in a vertical position and as the bent end extends below the
tool-block, it can be fed down close to a shoulder. The straight type
shown at _E_ is commonly used for turning steel or iron, and when the
point is drawn out narrower, it is also used for brass, although the
front is then ground without slope. Tool _F_ is for light finishing cuts
and broad feeds. The amount of feed per revolution of the work should
always be less than the width of the cutting edge as otherwise ridges
will be left on the turned surface. The offset tools _G_ and _H_ are for
finishing exterior and interior cylindrical surfaces. These tools also
have both vertical and horizontal cutting edges and are sometimes used
for first finishing a cylindrical and then a horizontal surface, or
_vice versa_. Tool _I_ is adapted to such work as cutting packing-ring
grooves in engine pistons, forming square or rectangular grooves, and
similar work. The parting tools _J_ and _K_ can also be used for forming
narrow grooves or for cutting off rings, etc. The sketch _K_ (Fig. 8)
indicates how a tool of this kind might be used for squaring a corner
under a shoulder. Tool _L_ is frequently used on boring mills for
rounding the corners of flywheel rims, in order to give them a more
finished appearance. It has two cutting edges so that either side can be
used as when rounding the inner and outer corners of a rim.
The turning tools of a vertical boring mill are similar, in many
respects, to those used in a lathe, although the shanks of the former
are shorter and more stocky than those of lathe tools. The cutting edges
of some of the tools also differ somewhat in form, but the principles
which govern the grinding of lathe and boring mill tools are identical,
and those who are not familiar with tool grinding are referred to
Chapter II, in which this subject is treated.
=Turning a Flywheel on a Vertical Mill.=--The turning of a flywheel is a
good example of the kind of work for which a vertical boring mill is
adapted. A flywheel should preferably be machined on a double-head mill
so that one side and the periphery of the rim can be turned at the same
time. A common method of holding a flywheel is shown in Fig. 9. The rim
is gripped by four chuck jaws _D_ which, if practicable, should be on
the inside where they will not interfere with the movement of the tool.
Two of the jaws, in this case, are set against the spokes on opposite
sides of the wheel, to act as drivers and prevent any backward shifting
of work when a heavy cut is being taken. The illustration shows the tool
to the right rough turning the side of the rim, while the left-hand tool
turns the periphery. Finishing cuts are also taken over the rim, at this
setting, and the hub is turned on the outside, faced on top, and the
hole bored.
[Illustration: Fig. 9. Turning the Rim of a Flywheel]
The three tools _A_, _B_ and _C_, for finishing the hole, are mounted in
the turret. Bar _A_, which carries a cutter at its end, first rough
bores the hole. The sizing cutter _B_ is then used to straighten it
before inserting the finishing reamer _C_. Fig. 10 shows the turret
moved over to a central position and the sizing cutter _B_ set for
boring. The head is centrally located (on this particular machine) by a
positive center-stop. The turret is indexed for bringing the different
tools into the working position, by loosening the clamping lever _L_ and
pulling down lever _I_ which disengages the turret lock-pin. When all
the flywheels in a lot have been machined as described, the opposite
side is finished.
[Illustration: Fig. 10. Tool B set for Boring the Hub]
[Illustration: Fig. 11. Diagrams showing Method of Turning and Boring a
Flywheel on a Double-head Mill having one Turret Head]
In order to show more clearly the method of handling work of this class,
the machining of a flywheel will be explained more in detail in
connection with Fig. 11, which illustrates practically the same
equipment as is shown in Figs. 9 and 10. The successive order in which
the various operations are performed is as follows: Tool _a_ (see sketch
_A_) rough turns the side of the rim, while tool _b_, which is set with
its cutting edge toward the rear, rough turns the outside. The direction
of the feeding movement for each tool is indicated by the arrows. When
tool _a_ has crossed the rim, it is moved over for facing the hub, as
shown by the dotted lines. The side and periphery of the rim are next
finished by the broad-nose finishing tools _c_ and _d_ (see sketch _B_).
The feed should be increased for finishing, so that each tool will have
a movement of say 1/4 or 3/8 inch per revolution of the work, and the
cuts should, at least, be deep enough to remove the marks made by the
roughing tools. Tool _c_ is also used for finishing the hub as indicated
by the dotted lines. After these cuts are taken, the outside of the hub
and inner surface of the rim are usually turned down as far as the
spokes, by using offset tools similar to the ones shown at _C_ and _D_
in Fig. 7. The corners of the rim and hub are also rounded to give the
work a more finished appearance, by using a tool _L_.
The next operation is that of finishing the hole through the hub. The
hard scale is first removed by a roughing cutter _r_ (sketch _C_), which
is followed by a "sizing" cutter _s_. The hole is then finished smooth
and to the right diameter by reamer _f_. The bars carrying cutters _r_
and _s_ have extensions or "pilots" which enter a close-fitting bushing
in the table, in order to steady the bar and hold it in alignment.
When the hole is finished, the wheel is turned over, so that the lower
side of the rim and hub can be faced. The method of holding the casting
for the final operation is shown at _D_. The chuck jaws are removed, and
the finished side of the rim is clamped against parallels _p_ resting on
the table. The wheel is centrally located for turning this side by a
plug _e_ which is inserted in a hole in the table and fits the bore of
the hub. The wheel is held by clamps which bear against the spokes.
Roughing and finishing cuts are next taken over the top surface of the
rim and hub and the corners are rounded, which completes the machining
operations. If the rim needs to be a certain width, about the same
amount of metal should be removed from each side, unless sandy spots or
"blow-holes" in the casting make it necessary to take more from one side
than from the other. That side of the rim which was up in the mold when
the casting was made should be turned first, because the porous, spongy
spots usually form on the "cope" or top side of a casting.
=Convex Turning Attachment for Boring Mills.=--Fig. 12 shows a vertical
boring mill arranged for turning pulleys having convex rims; that is,
the rim, instead of being cylindrical, is rounded somewhat so that it
slopes from the center toward either side. (The reason for turning a
pulley rim convex is to prevent the belt from running off at one side,
as it sometimes tends to do when a cylindrical pulley is used.) The
convex surface is produced by a special attachment which causes the
turning tool to gradually move outward as it feeds down, until the
center of the rim is reached, after which the movement is inward.
[Illustration: Fig. 12. Gisholt Mill equipped with Convex Turning
Attachment]
The particular attachment shown in Fig. 12 consists of a special
box-shaped tool-head _F_ containing a sliding holder _G_, in which the
tool is clamped by set-screws passing through elongated slots in the
front of the tool-head. In addition, there is a radius link _L_ which
swivels on a stud at the rear of the tool-head and is attached to
vertical link _H_. Link _L_ is so connected to the sliding tool-block
that any downward movement of the tool-bar _I_ causes the tool to move
outward until the link is in a horizontal position, after which the
movement is reversed. When the attachment is first set up, the turning
tool is placed at the center of the rim and then link _L_ is clamped to
the vertical link while in a horizontal position. The cut is started at
the top edge of the rim, and the tool is fed downward by power, the
same as when turning a cylindrical surface. The amount of curvature or
convexity of a rim can be varied by inserting the clamp bolt _J_ in
different holes in link _L_.
[Illustration: Fig. 13. Turning a Taper or Conical Surface]
The tools for machining the hub and sides of the rim are held in a
turret mounted on the left-hand head, as shown. The special tool-holder
_A_ contains two bent tools for turning the upper and lower edges of the
pulley rim at the same time as the tool-head is fed horizontally.
Roughing and finishing tools _B_ are for facing the hub, and the tools
_C_, _D_, and _E_ rough bore, finish bore, and ream the hole for the
shaft.
=Turning Taper or Conical Surfaces.=--Conical or taper surfaces are
turned in a vertical boring mill by swiveling the tool-bar to the proper
angle as shown in Fig. 13. When the taper is given in degrees, the
tool-bar can be set by graduations on the edge of the circular base _B_,
which show the angle _a_ to which the bar is swiveled from a vertical
position. The base turns on a central stud and is secured to the saddle
_S_ by the bolts shown, which should be tightened after the tool-bar is
set. The vertical power feed can be used for taper turning the same as
for cylindrical work.
[Illustration: Fig. 14. Turning a Conical Surface by using the Combined
Vertical and Horizontal Feeds]
Occasionally it is necessary to machine a conical surface which has such
a large included angle that the tool-bar cannot be swiveled far enough
around to permit turning by the method illustrated in Fig. 13. Another
method, which is sometimes resorted to for work of this class, is to use
the combined vertical and horizontal feeds. Suppose we want to turn the
conical casting _W_ (Fig. 14), to an angle of 30 degrees, as shown, and
that the tool-head of the boring mill moves horizontally 1/4 inch per
turn of the feed-screw and has a vertical movement of 3/16 inch per turn
of the upper feed-shaft. If the two feeds are used simultaneously, the
tool will move a distance _h_ of say 8 inches, while it moves downward a
distance _v_ of 6 inches, thus turning the surface to an angle _y_. This
angle is greater (as measured from a horizontal plane) than the angle
required, but, if the tool-bar is swiveled to an angle _x_, the tool, as
it moves downward, will also be advanced horizontally, in addition to
the regular horizontal movement. The result is that the angle _y_ is
diminished and if the tool-bar is set over the right amount, the
conical surface can be turned to an angle _a_ of 30 degrees. The
problem, then, is to determine what the angle _x_ should be for turning
to a given angle _a_.
[Illustration: Fig. 15. Diagram showing Method of Obtaining Angular
Position of Tool-head when Turning Conical Surfaces by using Vertical
and Horizontal Feeding Movements]
The way angle _x_ is calculated will be explained in connection with the
enlarged diagram, Fig. 15, which shows one-half of the casting. The sine
of the known angle _a_ is first found in a table of natural sines. Then
the sine of angle _b_, between the taper surface and center-line of the
tool-head, is determined as follows: sin_b_ = (sin_a_ × _h_) ÷ _v_, in
which _h_ represents the rate of horizontal feed and _v_ the rate of
vertical feed. The angle corresponding to sine _b_ is next found in a
table of sines. We now have angles _b_ and _a_, and by subtracting the
sum of these angles from 90 degrees, the desired angle _x_ is obtained.
To illustrate: The sine of 30 degrees is 0.5; then sin _b_ = (0.5 × 1/4)
÷ 3/16 = 0.6666; hence angle _b_ = 41 degrees 49 minutes, and _x_ =
90°-(30° + 41° 49') = 18 degrees 11 minutes. Hence to turn the casting
to angle _a_ in a boring mill having the horizontal and vertical feeds
given, the tool-head would be set over from the vertical 18 degrees and
11 minutes which is equivalent to about 18-1/6 degrees.
If the required angle _a_ were greater than angle _y_ obtained from the
combined feeds with the tool-bar in a vertical position, it would then
be necessary to swing the lower end of the bar to the left rather than
to the right of a vertical plane. When the required angle _a_ exceeds
angle _y_, the sum of angles _a_ and _b_ is greater than 90 degrees so
that angle _x_ for the tool-head = (_a_ + _b_) - 90 degrees.
=Turret-lathe Type of Vertical Boring Mill.=--The machine illustrated in
Fig. 16 was designed to combine the advantages of the horizontal turret
lathe and the vertical boring mill. It is known as a "vertical turret
lathe," but resembles, in many respects, a vertical boring mill. This
machine has a turret on the cross-rail the same as many vertical boring
mills, and, in addition, a side-head _S_. The side-head has a vertical
feeding movement, and the tool-bar _T_ can be fed horizontally. The
tool-bar is also equipped with a four-sided turret for holding turning
tools. This arrangement of the tool-heads makes it possible to use two
tools simultaneously upon comparatively small work. When both heads are
mounted on the cross-rail, as with a double-head boring mill, it is
often impossible to machine certain parts to advantage, because one head
interferes with the other.
The drive to the table (for the particular machine illustrated) is from
a belt pulley at the rear, and fifteen speed changes are available. Five
changes are obtained by turning the pilot-wheel _A_ and this series of
five speeds is compounded three times by turning lever _B_. Each spoke
of pilot-wheel _A_ indicates a speed which is engaged only when the
spoke is in a vertical position, and the three positions for _B_ are
indicated, by slots in the disk shown. The number of table revolutions
per minute for different positions of pilot-wheel _A_ and lever _B_ are
shown by figures seen through whichever slot is at _C_. There are five
rows of figures corresponding to the five spokes of the pilot-wheel and
three figures in a row, and the speed is shown by arrows on the sides of
the slots. The segment disk containing these figures also serves as an
interlocking device which prevents moving more than one speed
controlling lever at a time, in order to avoid damaging the driving
mechanism.
[Illustration: Fig. 16. Bullard Vertical Turret Lathe]
The feeding movement for each head is independent. Lever _D_ controls
the engagement or disengagement of the vertical or cross feeds for the
head on the cross-rail. The feed for the side-head is controlled by
lever _E_. When this lever is pushed inward, the entire head feeds
vertically, but when it is pulled out, the tool-bar feeds horizontally.
These two feeds can be disengaged by placing the lever in a neutral
position. The direction of the feeding movement for either head can be
reversed by lever _R_. The amount of feed is varied by feed-wheel _F_
and clutch-rod _G_. When lever _E_ is in the neutral position, the
side-head or tool-bar can be adjusted by the hand-cranks _H_ and _I_,
respectively. The cross-rail head and its turret slide have rapid power
traverse movements for making quick adjustments. This rapid traverse is
controlled by the key-handles _J_.
The feed-screws for the vertical head have micrometer dials _K_ for
making accurate adjustments. There are also large dials at _L_ which
indicate vertical movements of the side head and horizontal movements of
the tool slide. All of these dials have small adjustable clips _c_ which
are numbered to correspond to numbers on the faces of the respective
turrets. These clips or "observation stops" are used in the production
of duplicate parts. For example, suppose a tool in face No. 1 for the
main turret is set for a given diameter and height of shoulder on a part
which is to be duplicated. To obtain the same setting of the tools for
the next piece, clips No. 1, on both the vertical feed rod and screw
dials, are placed opposite the graduations which are intersected by
stationary pointers secured to the cross-rail. The clips are set in this
way after the first part has been machined to the required size and
before disturbing the final position of the tools. For turning a
duplicate part, the tools are simply brought to the same position by
turning the feed screws until the clips and stationary pointers again
coincide. For setting tools on other faces of either turret, this
operation is repeated, except that clips are used bearing numbers
corresponding to the turret face in use.
The main turret of this machine has five holes in which are inserted the
necessary boring and turning tools, drills or reamers, as may be
required. By having all the tools mounted in the turret, they can be
quickly and accurately set in the working position. When the turret is
indexed from one face to the next, binder lever _N_ is first loosened.
The turret then moves forward, away from its seat, thus disengaging the
indexing and registering pins which accurately locate it in any one of
the five positions. The turret is revolved by turning crank _M_, one
turn of this handle moving the turret 1/5 revolution or from one hole to
the next. The side-head turret is turned by loosening lever _O_. The
turret slide can be locked rigidly in any position by lever _P_ and its
saddle is clamped to the cross-rail by lever _Q_. The binder levers for
the saddle and toolslide of the side-head are located at _U_ and _V_,
respectively. A slide that does not require feeding movements is locked
in order to obtain greater rigidity. To illustrate, if the main tool
slide were to feed vertically and not horizontally, it might be
advisable to lock the saddle to the cross-rail, while taking the
vertical cut.
[Illustration: Fig. 17. Turning a Gear Blank on a Vertical Turret Lathe]
The vertical slide can be set at an angle for taper turning, and the
turret is accurately located over the center of the table for boring or
reaming, by a positive center stop. The machine is provided with a brake
for stopping the work table quickly, which is operated by lifting the
shaft of pilot-wheel _A_. The side-and cross-rails are a unit and are
adjusted together to accommodate work of different heights. This
adjustment is effected by power on the particular machine illustrated,
and it is controlled by a lever near the left end of the cross-rail.
Before making this adjustment, all binder bolts which normally hold the
rails rigidly to the machine column must be released, and care should be
taken to tighten them after the adjustment is made.
[Illustration: Fig. 18. Turning Gasoline Engine Flywheel on Vertical
Turret Lathe--First Position]
=Examples of Vertical Turret Lathe Work.=--In order to illustrate how a
vertical turret lathe is used, one or two examples of work will be
referred to in detail. These examples also indicate, in a general way,
the class of work for which this type of machine is adapted. Fig. 17
shows how a cast-iron gear blank is machined. The work is gripped on the
inside of the rim by three chuck jaws, and all of the tools required for
the various operations are mounted in the main and side turrets. The
illustration shows the first operation which is that of rough turning
the hub, the top side of the blank and its periphery. The tools _A_ for
facing the hub and upper surface are both held in one tool-block on the
main turret, and tool _A_{1}_ for roughing the periphery is in the side
turret. With this arrangement, the three surfaces can be turned
simultaneously.
[Illustration: Fig. 19. Turning Gasoline Engine Flywheel--Second
Position]
[Illustration: Fig. 20. Diagrams showing How Successive Operations are
Performed by Different Tools in the Turret]
The main turret is next indexed one-sixth of a revolution which brings
the broad finishing tools _B_ into position, and the side turret is also
turned to locate finishing tool _B_{1}_ at the front. (The indexing of
the main turret on this particular machine is effected by loosening
binder lever n and raising the turret lock-pin by means of lever _p_.)
The hub, side and periphery of the blank are then finished. When tools
_B_ are clamped in the tool-blocks, they are, of course, set for
turning the hub to the required height. The third operation is performed
by the tools at _C_, one of which "breaks" or chamfers the corner of the
cored hole in the hub, to provide a starting surface for drill _D_, and
the other turns the outside of the hub, after the chamfering tool is
removed. The four-lipped shell-drill _D_ is next used to drill the cored
hole and then this hole is bored close to the finished size and
concentric with the circumference of the blank by boring tool _E_, which
is followed by the finishing reamer _F_. When the drill, boring tool and
reamer are being used, the turret is set over the center or axis of the
table, by means of a positive center stop on the left-side of the turret
saddle. If it is necessary to move the turret beyond the central
position, this stop can be swung out of the way.
Figs. 18 and 19 illustrate the turning of an automobile flywheel, which
is another typical example of work for a machine of this type. The
flywheel is finished in two settings. Its position for the first series
of operations is shown in Fig. 18, and the successive order of the four
operations for the first setting is shown by the diagrams, Fig. 20. The
first operation requires four tools which act simultaneously. The three
held in tool-block _A_ of the turret, face the hub, the web and the rim
of the flywheel, while tool _a_ in the side-head rough turns the outside
diameter. The outside diameter is also finished by broad-nosed tool _b_
which is given a coarse feed. In the second operation, the under face of
the rim is finished by tool _c_, the outer corners are rounded by tool
_d_ and the inner surface of the rim is rough turned by a bent tool _B_,
which is moved into position by indexing the main turret. In the third
operation, the side-head is moved out of the way and the inside of the
rim is finished by another bent tool _B_{1}_. The final operation at
this setting is the boring of the central hole, which is done with a bar
_C_ having interchangeable cutters which make it possible to finish the
hole at one setting of the turret.
The remaining operations are performed on the opposite side of the work
which is held in "soft" jaws _J_ accurately bored to fit the finished
outside diameter as indicated in Fig. 19. The tool in the main turret
turns the inside of the rim, and the side-head is equipped with two
tools for facing the web and hub simultaneously. As the tool in the main
turret operates on the left side of the rim, it is set with the cutting
edge toward the rear. In order to move the turret to this position,
which is beyond the center of the table, the center stop previously
referred to is swung out of the way.
=Floating Reamer Holders.=--If a reamer is held rigidly in the turret of
a boring mill or turret lathe, it is liable to produce a hole which
tapers slightly or is too large. When a hole is bored with a
single-point boring tool, it is concentric with the axis of rotation,
and if a reamer that is aligned exactly with the bored hole is fed into
the work, the finished hole should be cylindrical and the correct size.
It is very difficult, however, to locate a reamer exactly in line with a
bored hole, because of slight variations in the indexing of the turret,
or errors resulting from wear of the guiding ways or other important
parts of the machine.
To prevent inaccuracies due to this cause, reamers are often held in
what is known as a "floating" holder. This type of holder is so arranged
that the reamer, instead of being held rigidly, is allowed a slight free
or floating movement so that it can follow a hole which has been bored
true, without restraint. In this way the hole is reamed straight and to
practically the same size as the reamer.
[Illustration: Fig. 21. Two Types of Floating Reamer Holders]
There are many different designs of floating holders but the general
principle upon which they are based is illustrated by the two types
shown in Fig. 21. The reamer and holder shown to the left has a
ball-shank _A_ which bears against a backing-up screw _B_ inserted in
the end of holder _C_ through which the driving pin passes. The lower
end of the reamer shank is also spherical-shaped at _D_, and screw-pin
_E_ secures the shell reamer to this end. It will be noted that the hole
in the shank for pin _E_ is "bell-mouthed" on each side of the center
and that there is clearance at _F_ between the shank and reamer shell;
hence the reamer has a free floating action in any direction. This
holder has given very satisfactory results.
[Illustration: Fig. 22. Multiple-spindle Cylinder Boring Machine]
The holder shown to the right is attached to the face of the turret by
four fillister-head screws. Sleeve _C_ is held in plate _A_ by means of
two steel pins _B_ which are tight in plate _A_ and made to fit freely
in bayonet grooves _D_. Reamer holder _E_ floats on sleeve _C_, the
floating motion being obtained through the four steel pins _G_ extending
into driving ring _F_. Two of the pins are tight in the holder _E_ and
two in sleeve _C_. The faces of sleeve _C_, driving ring _F_, and reamer
holder _E_ are held tightly against each other by means of spring _H_
which insures the reamer being held perfectly true. Spring _H_ is
adjusted by means of nut _I_ which is turned with a spanner wrench
furnished with each holder. The reamer is so held that its axis is
always maintained parallel to the center of the hole, and, at the same
time, it has a slight self-adjusting tendency radially, so that the hole
and reamer will automatically keep in perfect alignment with each
other.
=Multiple Cylinder Boring Machine.=--In automobile and other factories
where a great many gasoline engine cylinders are required,
multiple-spindle boring machines of the vertical type are commonly used.
The machine shown in Fig. 22 is a special design for boring four
cylinders which are cast _en bloc_ or in one solid casting. The work is
held in a box jig which has a top plate equipped with guide bearings for
holding the spindles rigidly while boring. The lower end of each spindle
has attached to it a cutter-head and the boring is done by feeding the
table and casting vertically. This feeding movement is effected by power
and it is disengaged automatically when the cutters have bored to the
required depth. The particular machine illustrated is used for rough
boring only, the cylinders being finished by reaming in another similar
machine. The cylinders are bored to a diameter of 3-5/8 inches, and
about 3/8 inch of metal is removed by the roughing cut. The spindles
have fixed center-to-center distances as the machine is intended for
constant use on cylinders of one size, so that adjustment is not
necessary. Of course, a special machine of this kind is only used in
shops where large numbers of cylinders of one design are required
continually. Some cylinder boring machines of the vertical type have
spindles which can be adjusted for different center-to-center distances
if this should be necessary in order to accommodate a cylinder of
another size.
CHAPTER VII
HORIZONTAL BORING MACHINES
A boring machine of the horizontal type is shown in Fig. 1. The
construction and operation of this machine is very different from that
of a vertical boring mill and it is also used for an entirely different
class of work. The horizontal machine is employed principally for
boring, drilling or milling, whereas the vertical design is especially
adapted to turning and boring. The horizontal type is also used for
turning or facing flanges or similar surfaces when such an operation can
be performed to advantage in connection with other machine work on the
same part.
The type of machine illustrated in Fig. 1 has a heavy base or bed to
which is bolted the column _C_ having vertical ways on which the
spindle-head _H_ is mounted. This head contains a sleeve or quill in
which the spindle _S_ slides longitudinally. The spindle carries cutters
for boring, whereas milling cutters or the auxiliary facing arm are
bolted to the end _A_ of the spindle sleeve. The work itself is attached
either directly or indirectly to the table or platen _P_. When the
machine is in operation, the cutter or tool revolves with the spindle
sleeve or spindle and either the cutter or the part being machined is
given a feeding movement, depending on the character of the work. The
spindle can be moved in or out by hand for adjustment, or by power for
feeding the cutter, as when boring or drilling.
[Illustration: Fig. 1. Lucas Horizontal Boring, Drilling and Milling
Machine]
The entire spindle-head _H_ can also be moved vertically on the face of
the column _C_, by hand, for setting the spindle to the proper height,
or by power for feeding a milling cutter in a vertical direction. When
the vertical position of the spindle-head is changed, the outboard
bearing block _B_ also moves up or down a corresponding amount, the two
parts being connected by shafts and gearing. Block _B_ steadies the
outer end of the boring-bar and the back-rest in which this block is
mounted can be shifted along the bed to suit the length of the work, by
turning the squared end of shaft _D_ with a crank. The platen _P_ has a
cross-feed, and the saddle _E_ on which it is mounted can be traversed
lengthwise on the bed; both of these movements can also be effected by
hand or power. There is a series of power feeding movements for the
cutters and, in addition, rapid power movements _in a reverse direction
from the feed_ for returning a cutter quickly to its starting position,
when this is desirable.
This machine is driven by a belt connecting pulley _G_ with an overhead
shaft. When the machine is in operation, this pulley is engaged with the
main driving shaft by a friction clutch _F_ controlled by lever _L_.
This main shaft drives through gearing a vertical shaft _I_, which by
means of other gears in the spindle-head imparts a rotary movement to
the spindle. As a machine of this type is used for boring holes of
various diameters and for a variety of other work, it is necessary to
have a number of speed changes for the spindle. Nine speeds are obtained
by changing the position of the sliding gears controlled by levers _R_
and this number is doubled by back-gears in the spindle-head and
controlled by lever _J_.
The amount of feed for the spindle, spindle-head, platen or saddle is
varied by two levers _K_ and _K_{1}_ which control the position of
sliding gears through which the feeding movements are transmitted. The
direction of the feed can be reversed by shifting lever _O_. With this
particular machine, nine feed changes are available for each position of
the spindle back-gears, making a total of eighteen changes. The feeding
movement is transmitted to the spindle-head, spindle, platen or saddle,
as required, by the three distributing levers _T_, _U_ and _V_, which
control clutches connecting with the transmission shafts or feed screws.
When lever _T_ is turned to the left, the longitudinal power feed for
the spindle is engaged, whereas turning it to the right throws in the
vertical feed for the spindle-head. Lever _U_ engages the cross-feed for
platen _P_ and lever _V_, the longitudinal feed for saddle _E_. These
levers have a simple but ingenious interlocking device which makes it
impossible to engage more than one feed at a time. For example, if lever
_T_ is set for feeding the spindle, levers _U_ and _V_ are locked
against movement.
The feeds are started and stopped by lever _M_ which also engages the
rapid power traverse when thrown in the opposite direction. This rapid
traverse operates for whatever feed is engaged by the distributing
levers and, as before stated, in a reverse direction. For example, if
the reverse lever _O_ is set for feeding the spindle to the right, the
rapid traverse would be to the left, and _vice versa_. The cross-feed
for the platen can be automatically tripped at any point by setting an
adjustable stop in the proper position and the feed can also be tripped
by a hand lever at the side of the platen.
All the different feeding movements can be effected by hand as well as
by power. By means of handwheel _N_, the spindle can be moved in or out
slowly, for feeding a cutter by hand. When the friction clamp _Q_ is
loosened, the turnstile _W_ can be used for traversing the spindle, in
case a hand adjustment is desirable. The spindle-head can be adjusted
vertically by turning squared shaft _X_ with a crank, and the saddle can
be shifted along the bed by turning shaft _Y_. The hand adjustment of
the platen is effected by shaft _Z_. The spindle-head, platen and saddle
can also be adjusted from the end of the machine, when this is more
convenient. Shafts _X_, _Y_ and _Z_ are equipped with micrometer dials
which are graduated to show movements of one-thousandth inch. These
dials are used for accurately adjusting the spindle or work and for
boring holes or milling surfaces that must be an exact distance apart.
=Horizontal Boring Machine with Vertical Table Adjustment.=--Another
horizontal boring machine is partly shown in Fig. 2. This machine is of
the same type as that illustrated in Fig. 1, but its construction is
quite different, as will be seen. The spindle cannot be adjusted
vertically as with the first design described, but it is mounted and
driven very much like the spindle of a lathe, and adjustment for height
is obtained by raising or lowering the work table. The design is just
the reverse, in this respect, of the machine shown in Fig. 1, which has
a vertical adjustment for the spindle, and a work table that remains in
the same horizontal plane. The raising or lowering of the table is
effected by shaft _E_, which rotates large nuts engaging the screws _S_.
Shaft _E_ is turned either by hand or power.
[Illustration: Fig. 2. Horizontal Boring and Drilling Machine with
Vertical Table Adjustment]
The main spindle is driven by a cone pulley _P_, either directly, or
indirectly through the back-gears shown. This arrangement gives six
spindle speeds, and double this number is obtained by using a two-speed
countershaft overhead. The motion for feeding the spindle longitudinally
is transmitted through a cone of gears, which gives the required
changes, to a pinion meshing with a rack which traverses the spindle.
The large handwheel _H_ and a corresponding wheel on the opposite side
are used for adjusting the spindle rapidly by hand. The yoke or outboard
bearing _B_ for the boring-bars can be clamped in any position along the
bed for supporting the bar as close to the work as possible.
Horizontal boring machines are built in many other designs, but they all
have the same general arrangement as the machines illustrated and
operate on the same principle, with the exception of special types
intended for handling certain classes of work exclusively. The
horizontal boring, drilling and milling machine is very efficient for
certain classes of work because it enables all the machining operations
on some parts to be completed at one setting. To illustrate, a casting
which requires drilling, boring and milling at different places, can
often be finished without disturbing its position on the platen after it
is clamped in place. Frequently a comparatively small surface needs to
be milled after a part has been bored. If this milling operation can be
performed while the work is set up for boring, accurate results will be
obtained (provided the machine is in good condition) and the time saved
that would otherwise be required for re-setting the part on another
machine. Some examples of work on which different operations are
performed at the same setting will be referred to later. The horizontal
boring machine also makes it possible to machine duplicate parts without
the use of jigs, which is important, especially on large work, owing to
the cost of jigs.
=Drilling and Boring--Cutters Used.=--Holes are drilled in a horizontal
machine by simply inserting a drill of required size either directly in
the spindle _S_ (see Fig. 1), or in a reducing socket, and then feeding
the spindle outward either by hand or power. When a hole is to be bored,
a boring-bar _B_{1}_ is inserted in the spindle and the cutter is
attached to this bar. The latter is then fed through the hole as the
cutter revolves. The distinction made by machinists between drilling and
boring is as follows: A hole is said to be drilled when it is formed by
sinking a drill into solid metal, whereas boring means the enlargement
of a drilled or cored hole either by the use of a single boring tool, a
double-ended cutter which operates on both sides of the hole, or a
cutter-head having several tools.
There are various methods of attaching cutters to boring-bars and the
cutters used vary for different classes of work. A simple style of
cutter which is used widely for boring small holes is shown at _A_ in
Fig. 3. The cutter _c_ is made from flat stock and the cutting is done
by the front edges _e_ and _e_{1}_, which are beveled in opposite
directions. The cutter is held in the bar by a taper wedge _w_ and it
is centered by shoulders at _s_, so that the diameter of the hole will
equal the length across the cutter. The outer corners at the front
should be slightly rounded, as a sharp corner would be dulled quickly.
These cutters are made in different sizes and also in sets for roughing
and finishing. The roughing cutter bores holes to within about 1/32 inch
of the finish size and it is then replaced by the finishing cutter. A
cutter having rounded ends, as shown by the detail sketch _a_, is
sometimes used for light finishing cuts. These rounded ends form the
cutting edges and give a smooth finish.
[Illustration: Fig. 3. Boring-cutters of Different Types]
Another method of holding a flat cutter is shown at _B_. The conical end
of a screw bears against a conical seat in, the cutter, thus binding the
latter in its slot. The conical seat also centers the cutter. A very
simple and inexpensive form of cutter is shown at _C_. This is made from
a piece of round steel, and it is held in the bar by a taper pin which
bears against a circular recess in the side of the cutter. This form
has the advantage of only requiring a hole through the boring-bar,
whereas it is necessary to cut a rectangular slot for the flat cutter.
[Illustration: Fig. 4. Boring with a Flat Double-ended Cutter]
Fig. 4 shows how a hole is bored by cutters of the type referred to. The
bar rotates as indicated by the arrow _a_ and at the same time feeds
longitudinally as shown by arrow _b_. The speed of rotation depends upon
the diameter of the hole and the kind of material being bored, and the
feed per revolution must also be varied to suit conditions. No definite
rule can be given for speed or feed. On some classes of work a long
boring-bar is used, which passes through the hole to be bored and is
steadied at its outer end by the back-rest _B_, Figs, 1 and 2. On other
work, a short bar is inserted in the spindle having a cutter at the
outer end. An inexpensive method of holding a cutter at the end of a bar
is shown at _D_, Fig. 3. The cutter passes through a slot and is clamped
by a bolt as shown. When it is necessary to bore holes that are "blind"
or closed at the bottom, a long boring-bar which passes through the work
cannot, of course, be used.
Sometimes it is necessary to have a cutter mounted at the extreme end of
a bar in order to bore close to a shoulder or the bottom of a hole. One
method of holding a cutter so that it projects beyond the end of a bar
is indicated at _E_. A screw similar to the one shown at _B_ is used,
and the conical end bears in a conical hole in the cutter. This hole
should be slightly offset so that the cutter will be forced back
against its seat. The tool shown at _F_ has adjustable cutters. The
inner end of each cutter is tapering and bears against a conical-headed
screw _b_ which gives the required outward adjustment. The cutters are
held against the central bolt by fillister-head screws _f_ and they are
clamped by the screws _c_. Boring tools are made in many different
designs and the number and form of the cutters is varied somewhat for
different kinds of work.
[Illustration: Fig. 5. Cutter-heads for Boring Large Holes]
=Cutter-heads for Boring Large Holes.=--When large holes are to be
bored, the cutters are usually held in a cast-iron head which is mounted
on the boring-bar. One type of cutter-head is shown in Fig. 5. This
particular head is double-ended and carries two cutters _c_. The
cutter-head is bored to fit the bar closely and it is prevented from
turning by a key against which a set-screw is tightened. By referring to
the end view, it will be seen that each cutter is offset with relation
to the center of the bar, in order to locate the front of the tool on a
radial line. The number of cutters used in a cutter-head varies. By
having several cutters, the work of removing a given amount of metal in
boring is distributed, and holes can be bored more quickly with a
multiple cutter-head, although more power is required to drive the
boring-bar. The boring-bar is also steadied by a multiple cutter-head,
because the tendency of any one cutter to deflect the bar is
counteracted by the cutters on the opposite side.
A disk-shaped head having four cutters is illustrated in Fig. 6. The
cutters are inserted in slots or grooves in the face of the disk and
they are held by slotted clamping posts. The shape of these posts is
shown by the sectional view. The tool passes through an elongated slot
and it is tightly clamped against the disk by tightening nut _n_. This
head is also driven by a key which engages a keyway in the boring-bar.
[Illustration: Fig. 6. Cutter-head with Four Boring Tools]
Two other designs of cutter-heads are shown in Fig. 7. The one
illustrated at _A_ has three equally spaced cutters which are held in an
inclined position. The cutters are clamped by screws _c_ and they can be
adjusted within certain limits by screws _s_. The cutters are placed at
an angle so that they will extend beyond the front of the head, thus
permitting the latter to be moved up close to a shoulder. The
cutter-heads shown in Figs. 5 and 6 can also be moved up close to a
shoulder if bent cutters are used as shown in the right-hand view, Fig.
5. The idea in bending the cutters is to bring the cutting edges in
advance of the clamping posts so that they will reach a shoulder before
the binding posts strike it. The arrangement of cutter-head _B_ (Fig. 7)
is clearly shown by the illustration.
Cutter-heads are often provided with two sets of cutters, one set being
used for roughing and the other for finishing. It is a good plan to make
these cutters so that the ends _e_ (Fig. 6) will rest against the bar or
bottom of the slot, when the cutting edge is set to the required radius.
The cutters can then be easily set for boring duplicate work. One method
of making cutters in sets is to clamp the annealed stock in the
cutter-head and then turn the ends to the required radius by placing the
head in the lathe. After both sets of cutters have been turned in this
way, they are ground to shape and then hardened.
[Illustration: Fig. 7. Cutter-heads equipped with Adjustable Tools]
Boring cutters intended for roughing and finishing cuts are shown in the
detail view Fig. 8 at _A_ and _B_, respectively. The side of the
roughing cutter _A_ is ground to a slight angle _c_ to provide clearance
for the cutting edge, and the front has a backward slope _s_ to give the
tool keenness. This tool is a good form to use for roughing cuts in cast
iron. The finishing tool at _B_ has a broad flat edge _e_ and it is
intended for coarse feeds and light cuts in cast iron. If a round
cutting edge is used for finishing, a comparatively fine feed is
required in order to obtain a smooth surface. The corners of tool _B_
are rounded and they should be ground to slope inward as shown in the
plan view. The top or ends _d_ of both of these tools are "backed off"
slightly to provide clearance. This clearance should be just enough to
prevent the surface back of the cutting edge from dragging over the
work. Excessive end clearance not only weakens the cutting edge, but
tends to cause chattering. As a finishing tool cuts on the upper end
instead of on the side, the front should slope backward as shown in the
side view, rather than sidewise as with a roughing cutter. The angle of
the slope should be somewhat greater for steel than cast iron, unless
the steel is quite hard, thus requiring a strong blunt tool.
[Illustration: Fig. 8. Boring Tools for Roughing and Finishing Cuts]
=Cylinder Boring.=--Fig. 9 illustrates the use of a cutter-head for
cylinder boring. After the cylinder casting is set on the platen of the
machine, the boring-bar with the cutter-head mounted on it is inserted
in the spindle. The bar _B_ has a taper shank and a driving tang similar
to a drill shank, which fits a taper hole in the end of the spindle. The
cutter-head _C_ is fastened to the bar so that it will be in the
position shown when the spindle is shifted to the right, as the feeding
movement (with this particular machine) is to be in the opposite
direction. The casting _A_ should be set central with the bar by
adjusting the work-table vertically and laterally, if necessary, and the
outer support _F_ should be moved close to the work, to make the bar as
rigid as possible.
The cylinder is now ready to be bored. Ordinarily, one or two roughing
cuts and one finishing cut would be sufficient, unless the rough bore
were considerably below the finish diameter. As previously explained,
the speed and feed must be governed by the kind of material being bored
and the diameter of the cut. The power and rigidity of the boring
machine and the quality of the steel used for making the cutters also
affect the cutting speed and feed. As the finishing cut is very light, a
tool having a flat cutting edge set parallel to the bar is ordinarily
used when boring cast iron. The coarse feed enables the cut to be taken
in a comparatively short time and the broad-nosed tool gives a smooth
finish if properly ground.
[Illustration: Fig. 9. Cylinder mounted on Horizontal Machine for
Boring]
The coarse finishing feed is not always practicable, especially if the
boring machine is in poor condition, owing to the chattering of the
tool, which results in a rough surface. The last or finishing cut should
invariably be a continuous one, for if the machine is stopped before the
cut is completed, there will be a ridge in the bore at the point where
the tool temporarily left off cutting. This ridge is caused by the
cooling and resulting contraction and shortening of the tool during the
time that it is stationary. For this reason independent drives are
desirable for boring machines.
Facing arms are attached to the bar on either side of the cylinder for
facing the flanges after the boring operation. The turning tool of a
facing arm is fastened to a slide which is fed outward a short distance
each revolution, by a star-wheel that is caused to turn as it strikes
against a stationary pin. By facing the flanges in this way, they are
finished square with the bore.
When setting a cylinder which is to be bored it should, when the design
will permit, be set true by the outside of the flange, or what is even
better, by the outside of the cylinder itself, rather than by the rough
bore, in order that the walls of the finished cylinder will have a
uniform thickness. The position of very large cylinders, while they are
being bored, is an important consideration. Such cylinders should be
bored in the position which they will subsequently occupy when
assembled. For example, the cylinder for a large horizontal engine
should be bored while in a horizontal position, as the bore is liable to
spring to a slight oval shape when the cylinder is placed horizontal
after being bored while standing in a vertical position. If, however,
the cylinder is bored while in the position in which it will be placed
in the assembled engine, this trouble is practically eliminated.
There is a difference of opinion among machinists as to the proper shape
of the cutting point of a boring tool for finishing cuts, some
contending that a wide cutting edge is to be preferred, while others
advocate the use of a comparatively narrow edge with a reduced feed. It
is claimed, that the narrow tool produces a more perfect bore, as it is
not so easily affected by hard spots in the iron, and it is also pointed
out that the minute ridges left by the narrow tool are an advantage
rather than a disadvantage, as they form pockets for oil and aid in
lubricating the cylinder. It is the modern practice, however, to use a
broad tool and a coarse feed for the light finishing cut, provided the
tool does not chatter.
The type of machine tool used for boring cylinders, and also the method
of procedure is determined largely by the size of the work and the
quantity which is to be machined. The turret lathe, as well as
horizontal and vertical boring mills, is used for this work, and in
automobile factories or other shops where a great many cylinders are
bored, special machines and fixtures are often employed.
[Illustration: Fig. 10. Boring a Duplex Cylinder on a Horizontal
Machine]
=Boring a Duplex Gasoline Engine Cylinder.=--The method of holding work
on a horizontal boring machine depends on its shape. A cylinder or other
casting having a flat base can be clamped directly to the platen, but
pieces of irregular shape are usually held in special fixtures. Fig. 10
shows how the cylinder casting of a gasoline engine is set up for the
boring operation. The casting _W_ is placed in a fixture _F_ which is
clamped to the machine table. One end of the casting rests on the
adjustable screws _S_ and it is clamped by set-screws located in the top
and sides of the fixture. There are two cylinders cast integral and
these are bored by a short stiff bar mounted in the end of the spindle
and having cutters at the outer end. A long bar of the type which passes
through the work and is supported by the outboard bearing _B_, could not
be used for this work, because the top of each cylinder is closed.
When one cylinder is finished the other is set in line with the spindle
by adjusting the work-table laterally. This adjustment is effected by
screw _C_, and the required center-to-center distance between the two
cylinders can be gaged by the micrometer dial _M_ on the cross-feed
screw, although positive stops are often used in preference. After the
first cylinder is bored, the dial is set to the zero position by
loosening the small knurled screw shown, and turning the dial around.
The feed screw is then rotated until the dial shows that the required
lateral adjustment is made, which locates the casting for boring the
second cylinder. The end of the casting is also faced true by a milling
cutter. Ordinarily, milling cutters are bolted directly to the spindle
sleeve _A_ on this particular machine, which gives a rigid support for
the cutter and a powerful drive.
[Illustration: Fig. 11. Cylinder turned around for Machining Valve
Seats]
The next operation is that of boring and milling the opposite end of the
cylinder. This end is turned toward the spindle (as shown in Fig. 11)
without unclamping the work or fixture, by simply turning the circular
table _T_ half way around. This table is an attachment which is clamped
to the main table for holding work that must be turned to different
positions for machining the various parts. Its position is easily
changed, and as the work remains fixed with relation to the table, the
alignment between different holes or surfaces is assured, if the table
is turned the right amount. In this case, the casting needs to be
rotated one-half a revolution or 180 degrees, and this is done by means
of angular graduations on the base of the table. The illustration shows
the casting set for boring the inlet and exhaust valve chambers. The
different cutters required for boring are mounted on one bar as shown,
and the casting is adjusted crosswise to bring each valve chamber in
position, by using the micrometer dial. The single-ended cutter _c_
forms a shallow circular recess or seat in the raised pad which
surrounds the opening. The cover joint directly back of the cylinders is
finished by milling.
[Illustration: Fig. 12. Boring Differential Gear Casing]
=Examples of Boring, Radial Facing and Milling.=--Another example of
boring, in which the circular table is used, is shown in Fig. 12. The
work _W_ is a casing for the differential gears of an automobile. It is
mounted in a fixture _F_ which is bolted to the table. The casting has
round ends, which are clamped in V-blocks, thus aligning the work. This
fixture has a guide-bushing _G_ which is centered with the bar and
cutter in order to properly locate the casting. There is a bearing at
each end of the casing, and two larger ones in the center. These are
bored by flat cutters similar to the style illustrated at _A_ in Fig. 3.
The cutter for the inner bearings is shown at _c_.
[Illustration: Fig. 13. Facing and Turning Flange of Differential Gear
Casing]
After the bearings are bored, the circular table is turned 90 degrees
and the work is moved closer to the spindle (as shown in Fig. 13) for
facing flange _F_ at right angles to the bearings. Circular flanges of
this kind are faced in a horizontal boring machine by a special
facing-arm or head _H_. For this particular job this head is clamped
directly to the spindle sleeve, but it can also be clamped to the
spindle if necessary. The turning tool is held in a slotted toolpost,
and it is fed radially for turning the side or face of the flange, by
the well-known star feed at _S_. When this feed is in operation the bent
finger _E_ is turned downward so that it strikes one of the star wheel
arms for each revolution; this turns the wheel slightly, and the
movement is transmitted to the tool-block by a feed-screw. The
illustration shows the tool set for turning the outside or periphery of
the flange. This is done by setting the tool to the proper radius and
then feeding the work horizontally by shifting the work-table along the
bed. By referring to Fig. 12 it will be seen that the facing head does
not need to be removed for boring, as it is attached to the spindle
driving quill and does not interfere with the longitudinal adjustment of
the spindle. This facing head is also used frequently for truing the
flanges of cylinders which are to be bored, and for similar work.
[Illustration: Fig. 14. Example of Work requiring Boring and Milling]
Fig. 14 shows another example of work which requires boring and milling.
This casting is mounted on a fixture which is bolted to the main table.
In this case the circular table is not necessary, because the work can
be finished without swiveling it around. After the boring is completed
the edge _E_ is trued by the large-face milling cutter _M_ bolted to the
spindle sleeve. The irregular outline of the edge is followed by moving
the table crosswise and the spindle vertically, as required.
=Fixture for Cylinder Lining or Bushing.=--A method of holding a
cylinder lining or bushing while it is being bored is shown in Fig. 15.
The lining _L_ is mounted in two cast-iron ring-shaped fixtures _F_.
These fixtures are circular in shape and have flat bases which are
bolted to the table of the machine. On the inside of each fixture, there
are four equally spaced wedges _W_ which fit into grooves as shown in
the end view. These wedges are drawn in against the work by bolts, and
they prevent the lining from rotating when a cut is being taken. This
form of fixture is especially adapted for holding thin bronze linings,
such as are used in pump cylinders, because only a light pressure
against the wedges is required, and thin work can be held without
distorting it. If a very thin lining is being bored, it is well to
loosen the wedges slightly before taking the finishing cut, so that the
work can spring back to its normal shape.
[Illustration: Fig. 15. Cylinder Lining mounted in Fixture for Boring]
[Illustration: Fig. 16. Detrick & Harvey Horizontal Boring Machine of
the Floor Type Boring Engine Bed Casting]
=Horizontal Boring Machine of Floor Type.=--The type of horizontal
boring, drilling and milling machine, shown in Fig. 16, is intended for
boring heavy parts such as the cylinders of large engines or pumps, the
bearings of heavy machine beds and similar work. This machine can also
be used for drilling and milling, although it is intended primarily for
boring, and the other operations are usually secondary. This design is
ordinarily referred to as the "floor type," because the work-table is
low for accommodating large heavy castings. The spindle _S_ which drives
the boring-bar, and the spindle feeding mechanism, are carried by a
saddle. This saddle is free to move vertically on the face of column
_C_ which is mounted on transverse ways extending across the right-hand
end of the main bed. This construction permits the spindle to move
vertically or laterally (by traversing the column) either for adjusting
it to the required position or for milling operations. The spindle also
has a longitudinal movement for boring. There is an outer bearing _B_
for supporting the boring-bar, which also has lateral and vertical
adjustments, so that it can be aligned with the bar.
The work done on a machine of this type is either clamped directly to
the large bed-plate _A_ (which has a number of T-slots for receiving the
heads of the clamping bolts) or, in some cases, a special fixture may be
used or an auxiliary table. Boring machines of this same general
construction are built in many different sizes. The main spindle of the
machine illustrated is driven by a motor located at the rear of the
vertical column _C_, the motion being transmitted to the spindle through
shafts and gearing. The casting _D_, shown in this particular
illustration, is for a steam engine of the horizontal type, and the
operation is that of boring the cylindrical guides or bearings for the
crosshead. These bearings have a diameter of 15-3/4 inches and are
37-3/4 inches long. In boring them, two roughing cuts and one finishing
cut are taken. The end of the casting, which in the assembled engine
bears against the cylinder, is then faced by means of a regular facing
arm.
After removing the boring-bar the table _E_ of the special fixture on
which the casting is mounted is turned one quarter of a revolution. A
large milling cutter 24 inches in diameter is next mounted on the
spindle of the machine, and one side of the main bearing, as well as the
pads for the valve-rod guide-bar brackets, are milled. The table is then
revolved and the opposite side of the main bearing is milled in the same
way, the table being accurately located in the different positions by an
index plunger _F_ which engages holes on the under side. The spindle is
now moved upward to allow the table to be turned so as to locate the
bearing end of the frame next to the headstock of the machine. The
milling cutter is then used to machine the inside and top surfaces of
the main bearing. By turning the fixture and not changing the position
of the casting after it is bolted into place, the various surfaces are
machined in the correct relation to one another without difficulty. This
is a good example of the work done on horizontal boring machines of the
floor type.
INDEX
PAGE
Acme flat turret lathe, examples of chuck work 219
Acme standard thread and tool for cutting 159
Acme standard thread gage 157
Acme thread tool, measuring width with vernier caliper 157, 158
Accumulation of errors 105, 106
Aligning lathe centers for cylindrical turning 16
Allowances, average, for forced fits 130
for different classes of fits 131
for driving fits 131
for forced fits of given pressure 133
for push fits 131
for running fits 131
for shrinkage fits 133
Aluminum, lubricant for machining 53
shape of tools for turning 53
speed and feed for machining 53
Angle-plate applied to lathe faceplate 48
Angles, gage for accurate measurement of 97
Apron of lathe 4, 5
Arbor or mandrel press 22
Arbors or mandrels for lathe work, types of 19
use of 17
Attachment, application of Hendey relieving 125
convex turning for vertical boring mill 259
for coarse threading in lathe 160
for spherical turning 113
for taper turning in lathe 88
Hendey relieving 123
Automatic chucking and turning machine, Potter & Johnston 223
Potter & Johnston, method of "setting-up" 227
Potter & Johnston, turning flywheel in 236
Back-gears of lathe 3, 4
Bardons & Oliver turret lathe, general description 178
Bored holes, measuring diameter of 41
Boring and reaming tools for vertical mill 251
Boring and turning mill, vertical, general description 242
vertical, holding and setting work 247
vertical, turning in 249
Boring and turning mill, vertical, turning tools for 253
Boring-bar cutters and methods of holding 280
Boring cutters for roughing and finishing cuts 285
Boring cylinders on horizontal machine 286
Boring holes to given center distance in lathe 51
Boring in lathe, example of 39
Boring large castings in lathe 49
Boring large holes, cutter-heads used for 283
Boring machine, horizontal 275
horizontal, examples of work on 289-297
horizontal, floor type 294
vertical, multiple-spindle type 274
Boring tool, lathe 40
Box-tools, different designs and examples of work 193
for general turret lathe work 190
Bradford belt-driven lathe, general description 1
Bradford quick change-gear type of lathe 173
Brass, speed for turning 52
tool for turning in lathe 52
"Bridle" or "hold-back" for lathe 26, 27
Bullard vertical turret lathe 264
examples of work 268
Button method of locating work 101
Caliper tool for taper turning 85
Calipers, methods of setting 10, 11
"Cat-head," application in lathe work 25
Center holes, incorrect and correct forms 32
Center indicator, use of 100
Centered stock, methods of facing ends 34
Centers, lathe, aligning for cylindrical turning 16
lathe, grinder for truing 34
Centering machine 30
Centering parts to be turned 28
Centering, precaution for tool steel 33
Change gears, calculating for thread cutting 167
compound, for thread cutting 170
for cutting fractional threads 171
for cutting metric pitches 171
for thread cutting 135
Chasing dial for "catching threads" when screw cutting 141
Chuck, inaccuracy from pressure of jaws 42
lathe, application of 37
setting work in 42
universal, independent and combination 36
Chucking and turning machine, Potter & Johnston automatic 223
Potter & Johnston automatic, method of "setting-up" 227
Potter & Johnston automatic, turning flywheel in 236
Chucking machine, New Britain, multiple-spindle type 238
Clearance angle for turning tools 66
Clearance of turning tools, meaning of 62, 63
Coarse threading attachment for lathe 160
Collapsing tap, Geometric 202
Combination chuck for lathe 36
Compound rest, applied to screw or thread cutting 143
applied to taper turning 95
Convex turning attachment for vertical boring mills 259
Copper, tool for turning in lathe 52
Crankshaft lathe, description of R. K. LeBlond special 108
operation of R. K. LeBlond 110
Crankshaft turning in engine lathe 107
Cross-slide stop for threading 155
Cuts, average depth for turning 75
roughing and finishing in lathe 12, 75, 76
Cutter-heads, for boring, equipped with adjustable tools 284, 285
for horizontal boring machine 283
Cutters, boring, roughing and finishing types 285
for boring-bars 280
Cutting lubricants for turning tools 77
Cutting speeds, average for turning 72
based on Taylor's experiments 71
effect of lubricant on 76
factors which limit speeds for turning 72
rules for calculating 74
Cylinder boring machine, multiple-spindle type 274
Cylinder boring on horizontal machine 286
Cylinder lining, fixture for holding when boring 293
Cylindrical turning, simple example of 6
Davis turret lathe, turning bevel gear blanks 212
turning worm-gear blanks 211
Depth of cut for turning, average 75
Detrick & Harvey horizontal boring machine, floor type 294
Dial for "catching threads" when screw cutting 141
Dial gage, testing concentricity of button with 103, 104
Die and tap holders, releasing 199
Die-heads, self-opening type 200
Disk gage, for angles and tapers 97
rules for setting 98, 99
Dogs or drivers, lathe, application of 16
Drill, flat, for lathe 44
Drilling and reaming in lathe 43
Drivers or dogs, lathe, application of 16
Driving fits, allowances for 131
Eccentric turning in lathe 106
Engine lathe, general description 1
Errors, accumulation of 105, 106
Faceplate, indexing for multiple-thread cutting 153
lathe, application of angle-plate to 48
lathe, holding work on 45
Facing ends of centered stock, different methods 34
Feed and depth of cut for turning, average 75
Feeds and speeds for turning based on Taylor's experiments 71
Filing and polishing in lathe 13
Finishing and roughing cuts in lathe 75, 76
Fits, allowances for different classes 131
different classes used in machine construction 129
driving, allowances for 131
forced, allowances for given pressure 133
forced, average allowance for 130
forced, pressure for 132
push, allowances for 131
running, allowances for 131
shrinkage, allowances for 133
Fixture for holding thin lining when boring 293
Flat drill and holder for lathe 44
Flat turret lathe, Acme, examples of chuck work 219
Hartness, example of turning 213
Jones & Lamson double-spindle type 221
Floating reamer holders 271
Flywheel, finishing in one setting in turret lathe 186
finishing in two settings in turret lathe 189
machining in turret lathe 184
turning in Potter & Johnston automatic 236
turning in vertical boring mill 255
Follow-rest for lathe 27
Forced fits, allowances for given pressure 133
average allowance for 130
pressure generally used in assembling 132
Fractional threads, change gears for cutting 171
Gage, disk, for angles and tapers 97
disk, rules for setting 98, 99
for testing V-thread tool 138
standard plug, for holes 42
thread, Acme standard 157
Geometric collapsing tap 202
Geometric self-opening die-head 200
Gisholt convex attachment for vertical mill 259
Gisholt vertical boring mill, general description 242
Grinder for truing lathe centers 34
Grinding lathe tools 62
Hartness flat turret lathe, example of turning 213
Hendey relieving attachment 123
application of, for relieving taps, cutters and hobs 125
"Hold-back" or "bridle" for lathe 26, 27
Hollow mills for turret lathe 198
Horizontal boring machine 275
Detrick & Harvey floor type 294
examples of work 289-297
Independent chuck for lathe 36
Index plate, change gear, for lathe 137
Indicator, center, use on lathe 100
for "catching threads" when screw cutting 141
test, truing buttons with 102, 103
thread, for lathe apron, principle of 142
Inserted cutter turning tools for lathe 58
Internal threading 154
Jones & Lamson double-spindle flat turret lathe 221
Knurling in lathe and tool used 122
Lard oil as a cutting lubricant 78
Lathe, boring holes to given center distance in 51
boring large castings in 49
boring small hole with 104, 105
cutting threads in 135
drilling small hole with 104
general description of Bradford 1
LeBlond crankshaft, operation of 110
Lo-swing, general description 115
method of handling when cutting threads 138
quick change-gear type 173
R. K. LeBlond special crankshaft 108
turret type, general description 178
Lathe centers, grinder for truing 34
Lathe chucks, application of 37
universal, independent and combination 36
Lathe faceplate, holding work on 45
Lathe follow-rest 27
Lathe steadyrest 23
application of, when boring 25
Lathe taper attachment 88
practical application of 90
Lathe tool grinding 62
Lathe tools, angle of clearance 66
angle of keenness 67
application of various types 56
slope of cutting edge 66, 67
Lathe turning tools, inserted-cutter type 58
set of tools for general work 54
Lead of thread, definition of 146
LeBlond, R. K., lathe for crankshaft turning 108
Left-hand thread, method of cutting 148
Lining, fixture for holding when boring 293
Lo-swing lathe, general description 115
example of multiple-turning 117
Lubricant, effect on cutting speed 76
for cooling turning tools 77
for machining aluminum 53
lard oil as a cutting 78
Lucas horizontal boring machine 275
Mandrel or arbor press 22
Mandrels or arbors for lathe work, types of 19
for lathe work, use of 17
Metric pitches, change gears for cutting 171
Micrometer for measuring threads 162
Mills, hollow, for turret lathe 198
Multiple-spindle chucking machine, New Britain 238
Multiple-thread cutting, indexing faceplate for 153
Multiple threads 146
method of cutting 150
setting tool when cutting 152
Multiple-turning in Lo-swing lathe 117
New Britain multiple-spindle chucking machine 238
Newall Engineering Co's fit allowances 131
Pistons, gasoline engine, turning in turret lathe 204
Piston rings, attachment for turning in turret lathe 210
turning in turret lathe 206
Piston turning in Pratt & Whitney turret lathe 208
Pitch, metric, change gears for cutting 171
Pitch of thread, definition of 146
Plug gage, standard 42
Polishing and filing in lathe 13
Potter & Johnston automatic chucking and turning machine 223
method of "setting-up" 227
turning flywheel in 236
Pratt & Whitney turret lathe, arranged for piston turning 208
equipped with piston ring turning attachment 210
Press for arbors or mandrels 22
Pressure generally used in assembling forced fits 132
Push fits, allowances for 131
Quick change-gear type of lathe 173
Reamer holders, floating type 271
Reaming and drilling in lathe 43
Releasing die and tap holders 199
Relieving attachment, Hendey 123
Relieving attachment, Hendey, application of 125
Relieving hobs or taps having spiral flutes 128
Rivett-Dock threading tool 164
Roughing and finishing cuts in lathe 75, 76
Running fits, allowances for 131
Screw cutting, calculating change gears for 167
compound gearing for 170
in engine lathe 135
method of handling lathe 138
selecting change gears for 135
with compound rest 143
Screws, cutting to compensate for shrinkage 165
metric, change gears for cutting 171
testing size of 161
Selecting type of turning machine 240
Shrinkage, cutting screws to compensate for 165
Shrinkage fits, allowances for 133
Side-tool, facing with 7
Speeds for turning, average 72
based on Taylor's experiments 71
effect of lubricant 76
factors which limit 72
rules for calculating 74
Spherical turning 111
attachments for 113
"Spider" for supporting bushing while turning 48, 49
Spiral flutes, method of relieving hobs or taps with 128
Square thread and method of cutting 149, 159
Steadyrest, application of when boring 25
for engine lathe 23
Stop for lathe cross-slide when threading 155
Tap and die holders, releasing type 199
Taper attachment for lathe 88
practical application of 90
Taper boring with taper attachment 90
Taper threading, position of tool for 154
Taper turning, adjustment of tailstock center for 82
by offset-center method 80
examples of 83
height of tool for 94
in vertical boring mill 261
in vertical mill with horizontal and vertical feeds 262
setting tailstock center with caliper tool 85
setting tailstock center with square 87
with compound rest 95
with taper attachment 92, 93
Tapers, gage for accurate measurement of 97
Tapers, rules for figuring 97
Test indicator, truing buttons with 102, 103
Test or center indicator for use on lathe 100
Thread cutting, calculating change gears for 167
compound gearing for 170
cross-slide stop used for 155
indexing faceplate for multiple threads 153
in engine lathe 135
internal 154
method of handling lathe 138
selecting change gears for 135
taper, position of tool for 154
with compound rest 143
Thread gage, Acme standard 157
Thread indicator for lathe apron 141, 142
Thread micrometer 162
Thread tool, Acme, measuring width with vernier caliper 157, 158
for cutting V-thread 138
Thread tools for standard threads 159
Threads, Acme standard, and tool for cutting 159
change gears for fractional 171
cutting to compensate for shrinkage 165
different forms of 144
left-hand, method of cutting 148
metric, change gears for cutting 171
multiple 146
multiple, method of cutting 150
multiple, setting tool when cutting 152
sharp V, and tool for cutting 159
square, and method of cutting 149, 159
testing size of 161
three-wire system for measuring 163
U. S. standard, and tool for cutting 146, 159
Whitworth standard, and tool for cutting 158, 159
worm, and tool for cutting 159, 160
Threading attachment, lathe, for coarse threads 160
Threading tool, Rivett-Dock 164
Tool grinding 62
Tools for lathe, set for general turning 54
Tools for turning, angle of clearance 66
angle of keenness 67
inserted-cutter type 58
slope of cutting edge 66, 67
Tools for turret lathe 190
Tools, lathe, application of various types 56
Turning, cylindrical, simple example of 6
eccentric 106
multiple, in Lo-swing lathe 117
with front and rear tools 114
Turning speeds, average for lathe 72
based on Taylor's experiments 71
factors which limit 72
rules for calculating 74
Turning tools, angle of clearance 66
angle of keenness 67
for aluminum 53
for brass 52
for copper 52
for lathe, position of 60
for lathe, set of, for general work 54
inserted-cutter type for lathe 58
slope of cutting edge 66, 67
Turret lathe, Bardons & Oliver, general description 178
examples of chuck work in Acme flat 219
Hartness flat, example of turning 213
Jones & Lamson double-spindle type 221
machining flywheels in 184
Pratt & Whitney arranged for piston turning 208
piston ring turning attachment for 210
tools for general work 190
turning bevel gear blanks in Davis 212
turning gasoline engine pistons in 204
turning piston rings in 206
turning worm-gear blanks in Davis 211
typical example of turret lathe work 181
Turret lathe tools, miscellaneous types 202
Turret lathe type of vertical boring mill 264
Type of turning machine, factors which govern selection 240
U. S. standard thread 159
method of cutting 146
Universal chuck for lathe 36
V-thread and tool for cutting 159
Vertical boring mill, Bullard turret lathe type 264
convex turning attachment 259
general description 242
holding and setting work 247
taper turning in 261
taper turning with horizontal and vertical feeds 262
tools for boring and reaming 251
turning flywheel in 255
turning tools for 253
Vertical turret lathe, Bullard, examples of work 268
Whitworth standard thread and tool for cutting 158, 159
Wire system for measuring threads 163
Worm thread and tool for cutting 159, 160
Transcriber's notes on changes made to text:
Left as in original:
use of degree, deg. and °; use of minute, min. and '.
Standardised to the most commonly used in the book:
backgear to back-gear; camshaft to cam-shaft; crankpin to
crank-pin; face-plate to faceplate; out-board to outboard;
over-hang to overhang; setscrew to set-screw; steady-rest
to steadyrest; subdivision(s) to sub-division(s); tail-stock
to tailstock; thumbscrew to thumb-screw; tool-post to toolpost;
tool-slide to toolslide; hand-wheel to handwheel; U.S. to U. S.
Page 64 had a blotched (illegible) word, this has been replaced by
(large and rigid) work.
Table of Contents: largely re-compiled to create one-to-one links
with named paragraphs and sections in text.
End of the Project Gutenberg EBook of Turning and Boring, by Franklin D. Jones
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