TRANSCRIBER’S NOTE
Italic text is denoted by _underscores_.
Bold text is denoted by =equal signs=.
Some minor changes to the text are noted at the end of the book.
Elementary Lathe Practice
AS ADAPTED TO THE TEACHING OF
MACHINE SHOP PRACTICE
IN TECHNICAL SCHOOLS.
BY T. J. PALMATEER
INSTRUCTOR IN MACHINE WORK
Leland Stanford Junior University
Copyright 1917, by T. J. Palmateer
FIRST EDITION
1917
Press of Nolte Bros. [Illustration: Union Mark] San Jose, California
PREFACE
The object of this instruction book is to help beginners to acquire
some familiarity with the more common lathe operations in the shortest
practicable period of time. For this purpose three exercises have
been designed with the view of giving the student the maximum amount
of information in the small amount of time usually allowed for this
purpose. The repetition of operations has therefore been avoided
wherever it was considered advisable and the time lost in simply
cutting off metal has been reduced as much as possible.
It is assumed that beginners will receive oral instruction on the
manipulation of the lathe, as in shifting the belt, the feed control,
etc. It will also be necessary for the instructor to give a practical
demonstration of most of the operations.
The lathe speeds for the different operations as indicated in this book
are only approximately correct since the actual cutting speed of the
tool in feet per minute varies with the size and kind of lathe used.
The instructor is expected to designate the proper speeds although
the belt connections given herein will generally be close enough for
beginners.
In case it is considered advisable to devote to the elementary lathe
operations less time than would be necessary to complete the three
exercises presented herein, very good results can be obtained if the
student will read all of the instructions carefully and then do only
Exercise No. 1 and piece B of Exercise No. 3.
The instructions here given are not intended as fixed rules for it is
recognized that some of the operations may be done by other methods
with equally good results.
T. J. PALMATEER.
Stanford University, Cal.
January 1917.
EXERCISE No. 1.
=FIT SHAFT TO COLLAR—RUNNING FIT=
[Illustration]
Cut off with a power hack-saw a piece of steel 6¹⁄₁₆ inches long from a
bar 1 inch in diameter. This will allow ¹⁄₁₆ of an inch for finishing
the ends and ³⁄₁₆ of an inch for turning the diameter.
An experienced lathe operator would use a piece of steel ⅝ of an inch
in diameter, but for beginners it is better to use larger stock to
allow for practice turning.
CENTERING
Center both ends in the centering machine. The size of the center in
this shaft should be from ³⁄₁₆ to ¼ of an inch in diameter. Larger work
should have deeper centers.
[Illustration: Fig. 1]
[Illustration: Fig. 2]
[Illustration: Fig. 3]
[Illustration: Fig. 4]
If a centering machine is not available, the work may be centered by
first locating the center with a pair of dividers and center punch and
then using a combination drill and countersink in the lathe as shown
in Fig. 1. In this case the work is held by hand to prevent it from
turning. As this work is to be turned, it is necessary to center it
only approximately true.
=Accurate Centering.=—When the work is to be centered accurately, it
may be done by putting one end in the lathe chuck and the other in a
steady rest. A pointed tool is then used in the tool post as shown in
Fig. 2. The point of this tool has an angle of 60 degrees, the same as
the lathe centers, and is ground like a flat drill so that it cuts on
both sides.
After the shaft is centered with this tool, a center hole about ⅛ of an
inch in diameter should be drilled. This is done by holding the drill
in the tail-stock of the lathe with a drill-chuck, as shown in Fig. 3.
The object of this center hole is to give the center of the shaft a
bearing on the lathe center a short distance back from the point, as at
A in Fig. 4.
PLACING WORK IN LATHE
The work is made to rotate on the lathe centers by fastening a lathe
dog to the shaft at the head-stock end, as shown at A in Fig. 5.
[Illustration: Fig. 5]
The tail-stock center is adjusted so that the shaft will rotate freely,
yet be tight enough to allow no slack, or lost motion. Since the shaft
rotates on this center, it should be kept well lubricated by using
machine oil, or a mixture of graphite and oil.
To get the best results in turning this sort of work, it is necessary
to face both ends before turning and to rough turn the whole piece to
within about 0.03, or 0.04 of an inch of the finished size before any
part of it is finished. However, it is not always necessary to do this.
The object of first rough turning the shaft all over is to remove the
internal strains of the steel and to wear the centers down to a good
bearing before any finishing cuts are taken. The purpose of facing the
ends is to get them square, or true, and smooth.
FINISHING END OF SHAFT
To face the ends, use a regular turning tool starting to cut from the
outside and feeding by hand towards the center with the cross feed.
Such a tool will leave a ridge near the center, as shown in Fig. 6.
This ridge is cut off with a sharp pointed, side cutting tool, as shown
in Fig. 7, which is also used for taking the finishing cut across the
whole end of the bar. When taking this finishing cut, lard oil, or some
other lubricant, should be used.
[Illustration: Fig. 6]
[Illustration: Fig. 7]
After the finishing cut has been taken, any small ridge, or fin that
remains at the edge of the center is removed by slightly changing the
angle of the tool in the tool post and allowing about ¹⁄₆₄ of an inch
play between the centers. Having the work loose like this when the
lathe is running, allows the extreme point of the side tool to extend
beyond the edge of the center and cut a smooth end.
The lathe should run slow for the finishing cut and fast when the
regular turning tool is used.
TURNING THE SHAFT
The first, or roughing cut, is taken with a high-speed steel tool, or
bit, fastened in a tool holder. The tool holder is clamped in the tool
post of the lathe so that the point of the tool is at, or a little
above, the center, or axis, of the lathe, as in Fig. 8.
If the point of the bit is too high, it is easy to see that, as the
shaft rotates, the tool will not cut at all, Fig. 9. In case the tool
is set below the center, the cutting action is very poor so that
turning tools are never set as in Fig. 10.
[Illustration: Fig. 8]
[Illustration: Fig. 9]
[Illustration: Fig. 10]
[Illustration: Fig. 11]
=Speed of the Lathe.=—In taking the heavy roughing cuts, the belt
may be placed on the second largest step of the cone, while for the
finishing cuts the lathe should run a little faster, say with the belt
in the next smaller step.
=Grinding Turning Tool.=—The front, or point, and the sides of the tool
are ground at an angle, which is called the clearance. If the tool has
too little clearance, it will not cut freely, while if it has too much
clearance, the point will be so thin that it will break off or become
dull quickly.
The top of the tool is also ground at an angle. This is called the
rake. If the tool has too little rake, it will not cut freely and if it
has too much, the edge will soon break down.
It requires some practice for a beginner to learn the proper rake and
clearance that should be given to a tool. Fig. 11 shows a tool ground
with clearance and rake that will give very good results.
=Direction Tool Should Travel.=—The depth of the first cut should be
about ¹⁄₁₆ of an inch and the travel of the tool should always be from
the tail-stock end towards the head-stock. If the travel is in the
opposite direction, the pressure on the tail-stock center is increased,
causing it to heat quickly.
The length of the cut should be as great as possible without the lathe
dog striking the tool, or cross-rest.
=Adjusting the Lathe to Turn Straight.=—After the first cut, the work
should be calipered and if it is not the same diameter at both ends
the tail-stock should be adjusted so that the lathe will turn straight.
The tail-stock adjustment is made by loosening the main clamping nut B
and one of the screws C and then tightening the other screw C on the
opposite side of the tail-stock, Fig. 5.
If the shaft is larger at the tail-stock end, the tail-stock should be
moved towards the front of the lathe one half the difference between
the diameters of the shaft at the two ends.
In doing close work, the tail-stock should be adjusted as closely as
possible, but in this case if it is off center only a little, say 0.002
or 0.003 of an inch, it will be close enough providing it is set so
that the shaft will be turned larger at the head-stock end. If the
tail-stock is set so that the shaft is turned larger at the tail-stock
end, the shaft will be too small at the other end after the finishing
cut is taken.
=Fitting Shaft to the Collar.=—After the roughing cut is taken and the
lathe has been adjusted so that it turns approximately straight, the
end of the shaft is turned for about ¼ of an inch so that it will just
fit the hole in the collar, shown in the drawing of Exercise 1. To
measure this: first set the inside calipers to the diameter of the hole
in the collar, then set the outside calipers to the inside calipers and
caliper the shaft as accurately as possible. For a final test of this
diameter, remove the work from the lathe and try it with the collar
itself.
The advantage of turning but ¼ of an inch at the end of the shaft is
this; if the finishing cut were set too deep, only ¼ of an inch of
the shaft would be too small, while if this cut were taken the whole
length, the entire shaft would be too small.
After the shaft has been turned at the end so that it fits the collar,
the rest of the shaft should be turned a little larger, say 0.002 or
0.003 of an inch, in diameter. This will leave enough to finish with a
file.
=Filing.=—The object of filing is to take out the tool marks, but it
is also found to be much easier to make a close fit by filing off the
last 0.002 or 0.003 of an inch than to take so small a cut with a tool.
The amount of allowance for filing depends upon the character of the
finishing cut. Since the less filing required the better, the finishing
cut should be made as smooth as possible.
The tool used for the roughing cut may also be used for finishing, but
it is usually necessary to re-sharpen it. After it is reset in the tool
post, the point should be flattened a little wider than the pitch of
the feed, say about ¹⁄₃₂ of an inch, and parallel with the work. This
is done with an oilstone.
For filing work on a lathe, a single cut file is used. This is called a
lathe, or mill file.
The stroke of the file should be slow, steady, and straight across
the shaft. The lathe should run a little faster for filing than for
turning, the object being to have the work make several revolutions for
a single stroke of the file. If the lathe runs too slow and the stroke
of the file is too fast, the shaft, instead of being filed round, will
have a series of flat places on the surface.
After the work is finished as close to the dog as possible, reverse it
in the lathe and finish that part where the dog was fastened.
EXERCISE No. 2.
[Illustration]
The finished shaft in Exercise No. 1 may be used for Exercise No. 2.
Place the shaft in the bench vise and with a rule and scriber lay off
the dimensions: 1¾ in., 3 in., and 1¼ in. Then center punch the lines
just deep enough so that they can be easily seen when the work is in
the lathe.
Turn the large end first.
When it is necessary to turn a fixed distance, or to a line as in this
case, it is well to disconnect the feed when the tool is within about ⅛
of an inch from the end of the cut and to feed the tool the rest of the
distance by hand. If this is not done, the tool may travel farther than
it is intended to.
It is better to turn the portions to be threaded a little under rather
than over size. For if they are over size, the threads will not fit the
standard size nut, but if under size the threads do not need to be cut
so deep in order to fit the nut.
For measuring the diameters of this piece set the calipers as
accurately as possible by measuring from the end of the rule, as shown
in Fig. 12.
[Illustration: Fig. 12]
[Illustration: Fig. 13]
=Cutting Recess.=—The surface at the end as well as the recesses
between the threads and the taper are cut with a square-nose, or
cutting-off tool, Fig. 13.
This tool should have a sharp smooth edge, the point being set level
with the center of the lathe.
To produce a smooth finished surface lard oil should be used with a
slow feed and lathe speed.
After the end is turned to size, reverse the work in the lathe and turn
the other end and the taper before cutting the threads.
=Turning Taper.=—The drawing calls for a taper of 1 inch per foot. This
is cut by using a taper attachment, or by setting the tail-stock off
center. As most lathes are not provided with a taper attachment, the
latter method will be used.
If the work was 12 inches long, the tail-stock would be moved off
center ½ inch to turn a taper of 1 inch per foot. It being only 6
inches long, the tail-stock is set off center but half that amount, or
¼ inch.
Before taking the finishing cut, caliper both ends to prove that the
lathe is cutting the correct taper.
THREAD CUTTING
The threads are cut to fit ½ inch and ⅝ inch nuts having United States
Standard threads. These threads are flattened at the top and bottom to
the amount of ⅛ of the pitch instead of being sharp pointed as in the
case of Standard V-threads.
=Pitch.=—The pitch of the thread is the distance from the center of one
thread to the center of the one adjoining. On the end of the exercise
having 13 threads per inch the pitch is ¹⁄₁₃ of an inch so that the
width of the flat at the top and bottom of this thread should be ⅛ of
¹⁄₁₃ of an inch, or about .009 of an inch.
=Lead.=—The lead of the thread is the distance a nut on the screw will
travel in making one complete turn. For single threads the pitch and
lead are the same, but for double threads the lead is twice the pitch.
=Grinding Tool.=—The sides of U. S. S. threads form an angle of 60
degrees. To cut this thread in a lathe, a tool the same shape as the
threads is used. A gauge for grinding this tool accurately is shown in
Fig. 14.
[Illustration: Fig. 14]
[Illustration: Fig. 15]
[Illustration: Fig. 16]
If a U. S. S. thread gauge is not available, the tool can be ground
with the aid of a regular thread and center gauge, shown in Fig. 15.
With such a gauge the angle can be ground accurately, but it will be
necessary to measure the flat point with a rule.
The top of the tool should be ground so that it will be approximately
in a horizontal plane when set in the lathe.
Where the thread to be cut is as fine as 13 per inch the flat surface
at the point of the tool is so small that the extreme point can be
oil-stoned off instead of being taken off with the grinding wheel. The
flat point should never be wider than the standard size, but if it is a
little too narrow it will make very little difference in ordinary lathe
work.
=Setting Tool.=—To set the tool so that both sides of the thread will
have the same angle, the thread gauge is used as shown in Fig. 16. The
tool should be set on a level with the center of the lathe.
=How Lathe is Geared.=—To cut 13 threads per inch the work must make
13 revolutions while the carriage, which carries the tool, travels one
inch. For this purpose the lathe spindle is connected to the lead
screw with the proper size gears and the lead screw to the carriage by
a split nut. This split nut is back of the carriage apron and is opened
and closed by the lever E, Fig. 17.
[Illustration: Fig. 17
A. Index Plate
B. Stud Gear
C. Screw Gear
D. Intermediate or Idle Gear
E. Lever for connecting Carriage to Lead Screw
J. Lever for Disconnecting and Reversing Feed
K. Adjustable Stop for Thread Cutting
]
[Illustration: Fig. 18]
If the lead screw of the lathe has 6 threads per inch, the gearing to
cut 13 threads per inch must have the same ratio as 6 is to 13. To cut
16 threads the ratio would be 6 to 16.
It is not necessary to figure the size of gears for the different
threads as all lathes are provided with an index plate that designates
the proper size gears to be placed on the stud B and screw C, Fig. 17,
for the desired thread.
=To Set Change Gear.=—To change these gears, first loosen the nuts
holding the stud and screw gears B and C. Next loosen the nut G. This
will allow the intermediate gear to drop away from the stud gear B.
Then loosen the nut H so that the intermediate gear can be drawn back
away from the gear on the lead screw C.
When the gears are put together, they should be set so that there will
be a little slack, or lost motion, between the different gears. If they
are set too close together, they will make a great deal of noise when
running and there is also danger of breaking the teeth.
While all lathes are not designed alike the method of changing the
gears is very much the same on all machines except those having the
quick change-gear device. With a lathe having such a device, instead of
changing the gears on the stud and screw the same result is obtained by
shifting a combination of levers.
=Why Feed Should Be Disconnected.=—The mechanism that controls the
feed, or travel, of the tool when cutting threads is independent of
that used for the feed when doing plain turning. The two feeds usually
run at different speeds so that if they are both in action at the same
time the gears in the carriage will break. For this reason all lathes
are provided with some means of disconnecting the feed used for plain
turning when cutting threads.
To disconnect the feed on the lathe shown in Fig. 17, move the lever J
to the central, or neutral, position. This should always be done before
starting to cut the threads.
=Speed of Lathe.=—The lathe should run slower for cutting threads than
for plain turning. With most lathes if the belt is on the largest step
of the cone it will give about the right speed for cutting the threads
in this exercise.
The object of running the lathe slow is to give the operator time to
draw back the tool at the end of the cut and to obtain a smoother cut.
If the speed of the lathe is too fast, the cutting action will be so
quick that the tool, instead of cutting clean and smooth, will tear out
the metal leaving a rough surface.
The slower the lathe runs the easier it is to cut the threads, but it
will also take longer to do the job. It therefore requires practical
experience to determine the proper speed to be used for cutting the
different size threads.
=Chamfering.=—After the lathe and tool are properly set, chamfer off
the sharp corners where the threads begin and end with the side of the
thread tool. The depth of this cut should be about the same as that
of the threads when finished. If the corners are not chamfered, the
threads, when cut, will form a very thin edge, or fin, at the ends.
=Use of Adjustable Stop.=—To regulate the depth of each cut an
adjustable stop is used as shown at K. First move the tool so that the
point just touches the work, then adjust the screw on the attachment
K so that the cross-rest will not go in any farther. Now move the
carriage by hand until the point of the tool is a little past the
tail-stock end of the work; close the split nut on the lead screw with
the lever E; and turn the screw on the attachment K so that the tool
can be moved in just enough to take a very light cut.
Start the lathe and when the tool has reached the end of the cut
back it out and reverse the lathe. By reversing the lathe the tool
is returned to the starting point without disconnecting any of the
gearing. The object of drawing the tool back is to prevent it from
dragging on the work during its return.
The tool will never travel over the same path on the reverse as on the
forward movement of the lathe on account of the slack, or lost motion,
in the gears.
This first cut is taken to prove that the lathe is properly geared, so
the work should be measured with a rule, or screw pitch gauge.
Adjust the screw at K until the tool can be moved in deeper for the
next cut and repeat the operation until the thread is nearly finished.
Then the tool should be reset so that it will cut on only one side at a
time.
=Finishing Side of Thread.=—When roughing out the threads, the tool
cuts on both sides of the point since it is fed straight into the work.
It is much easier, though, to finish the threads smooth if the tool
cuts on one side only. This is done by rapping the end of the tool
holder so that it is turned in the tool post just enough to change the
position of the point of the tool about .01, or .02 of an inch.
To prove that the tool is set over the proper amount, turn the lathe
forward by hand a few revolutions, to take out all the slack, or lost,
motion in the gears, then move the tool into the groove of the thread
until one side just touches the side of the thread. The other side of
the tool should then be about .01, or .02 of an inch away from the side
of the thread.
After the tool is properly adjusted, set the stop K. The tool is then
drawn back and the lathe reversed until the tool is at the end of the
work ready for a cut. It usually requires several finishing cuts to
take out all the rough marks left by the roughing cuts.
When this side of the thread is finished, the other side is finished in
the same manner.
If the lathe is provided with a compound rest, a somewhat different
procedure is usually followed since the rest can be set at an angle of
30 degrees with the work, as in Fig. 18.
In this case the tool is moved in by turning the small hand-crank M
until the side at O has been cut to the proper depth. While making
these first cuts, the stop K is merely used to bring the cross-rest to
the same position each time. The tool is then drawn back slightly with
the hand-crank M and the stop K adjusted so that the tool can be moved
straight in by means of the hand-crank Q. This will finish the other
side of the thread at P.
To determine when the thread is cut to the proper size the work is
removed from the lathe and tested with a standard nut having U. S. S.
threads.
After the threads are cut on this end of the exercise, it is reversed
in the lathe and the other end threaded in a similar manner.
To prevent the screw of the dog from marring the portion already
threaded two nuts should be screwed on and the dog fastened to the nuts.
=How to Reset the Tool.=—When cutting threads of this size and larger,
the tool usually becomes dull from taking the heavy roughing cuts. It
is then necessary to resharpen it before taking the fine finishing cuts.
To reset the tool in the lathe first get the angles correct, as shown
in Fig. 16. Then revolve the lathe forward by hand to take up the slack
in the gears and move the tool in close to the threads. If the tool is
in a position so that it will cut too much off one side of the thread,
it may be changed by disengaging the reversing gears with the lever R
and turning the lathe by hand. When the tool is in the proper position
relative to the groove of the thread, the reverse gear lever R is reset.
In a case where the tool is off the desired position only a very
little, it may be corrected by the rapping process.
If the lathe has a compound rest the tool may be brought to the correct
position by turning the hand-crank M.
It would be well for beginners to practice thread cutting on a piece of
scrap steel before trying to cut them on the exercise.
EXERCISE No. 3.
CAST IRON FINISHED ALL OVER.
[Illustration]
=Sequence of Operations=:
1. Finish the inside of Piece A.
2. Drill and Ream the hole in Piece B.
3. Mount B on mandrel and finish outside.
4. Screw A on B and finish the outside of A.
[Illustration: Piece A.
10 Thrds. per 1″ U. S. S.
Fig. 19 Rough Casting]
[Illustration: Fig. 20 Finished Casting]
USE OF 4-JAW CHUCK.
To machine the inside of piece A it is necessary to hold it in the
lathe by means of an independent four-jaw chuck, as shown in Fig. 21.
Work of this kind is usually chucked so that the outside surfaces will
be within ¹⁄₃₂ of an inch of running true.
[Illustration: Fig. 21]
The process of chucking the work is as follows:
=Centering Work in the Chuck.=—Place the work in the chuck and adjust
the jaws until they are all at approximately equal distances from the
circles on the face of the chuck. Then put a cutting-off tool loosely
in the tool post and move it close to the work and as near as possible
to the end of the chuck jaws. Revolve the lathe by hand to prove if
the work is centered. If it is not centered to within ¹⁄₃₂ of an inch,
readjust the jaws until it is. Now move the cutting-off tool to the end
of the work and turn the lathe by hand. If the end runs out of true,
rap it with a hammer at such points as will correct its position.
=Advantage of Proper Chucking.=—Fig. 21 shows the work held by the
middle step of the cone. One reason for holding it in this way is to
permit the rough turning of the larger step while in the chuck. If the
work were held by the small end, it would be apt to work loose when
taking the heavy roughing cuts on account of the distance that the work
projects out and the small diameter on which the chuck grips compared
with that of the large end which is to be turned.
ROUGH TURNING AND BORING.
After the work has been properly chucked, rough turn the end and the
largest diameter to within ¹⁄₃₂ of an inch of the finished size.
All cast iron has a hard surface, or scale, from ¹⁄₆₄ to ¹⁄₃₂ of an
inch deep so that it is necessary to run the lathe slower for the first
cut than for those made after the scale has been removed. In taking
this first cut the tool should be set deep enough to permit the point
to cut under the scale.
=Speed of Lathe.=—The speed of the lathe in taking the roughing cut on
work of this size should be about right if the belt is on the smallest
step of the cone and the back gears are used. After the scale is
removed, the lathe may be run faster.
A beginner will require experience before being able to determine the
proper speeds and feeds for the different kinds of lathe work.
=Advantage of Roughing Inside.=—As the inside of piece A must fit the
outside of the piece B, the 1⅛ inch hole, the threads, and the taper
must be machine true with each other, or else A will not fit into B
properly. Now if the taper should be finished and the work moved in the
chuck before the threads and the 1⅛ inch hole are finished, they would
not be true with each other. For this reason it would be well to rough
bore the inside to within ¹⁄₃₂ of an inch of the finished size before
any of these three parts are finished.
=Roughing Inside.=—To rough bore the taper use a regular turning tool.
Set the compound rest to the correct angle and feed the tool in at that
angle.
If the lathe is not provided with a compound rest, the taper may be
rough bored by turning both feeds by hand and following the cored
surface as closely as possible.
The cored hole in the rough casting, Fig. 19, is ¹⁵⁄₁₆ of an inch in
diameter which allows ³⁄₁₆ of an inch for finishing the 1⅛ inch hole
and ⁵⁄₁₆ for the portion where the threads are to be cut.
=Use of Flat Drill.=—To rough bore the hole a 1¹⁄₁₆ flat, or lathe,
drill is used as shown in Fig. 21. The holder A is clamped in the tool
post so that the slot in it will hold the drill at the center of the
lathe. If the drill is held above or below the center, the hole will be
drilled larger than the drill. To prove that the slot in the holder is
at the center, move it close to the tail-stock center. After the holder
is properly set, move it as close to the work as possible and feed the
drill into the exercise by turning the hand-crank on the tail-stock.
This drill removes the hard surface, or scale, and also trues up, or
centers, the hole to within ¹⁄₆₄, or ¹⁄₃₂ of an inch. Now enlarge the
portion of the hole where the threads are to be cut with a 1³⁄₁₆ drill.
To determine when this drill has been fed in far enough, mark on the
drill with a piece of chalk the distance from the end of the work to
the point where the recess is to be cut. By sighting across the end of
the work the operator can then see when the drill has been fed in the
proper distance.
=Use of Boring Bar.=—To cut the square shoulder where the threads begin
and the recess where they end, use a tool and boring bar, as shown in
Fig. 22, held in the tool post. The width of this tool is ⁵⁄₃₂ of an
inch so that it will be necessary to take two cuts to make the recess
wide enough. Such a narrow tool is used because it is less liable to
chatter.
[Illustration: Fig. 22]
This tool is ground with clearance at the sides as well as at the front
and it should also be noticed that it is wider at the cutting edge than
back close to the boring bar. This is done so that when the tool is fed
into the work there will be little, or no chance of its binding on the
side.
To obtain the correct setting for the tool, move the boring bar into
the hole and bring it up close to one side. The tool should then be
adjusted until its cutting edge is parallel to the elements of this
surface.
The work is now all roughed out so that it makes very little difference
which of the three fitting parts is finished first.
FINISHING INSIDE
The 1⅛ inch hole has been drilled with a ¹¹⁄₁₆ inch lathe drill, but
as such a tool cannot be relied upon to drill true to center, or size,
it is necessary to turn it out with a boring tool. With this tool
the hole can be bored true to center and within .01 of an inch of the
finished size.
The boring bar used in this case is the same as shown in Fig. 22, but
the cutter has a rounded point and is similar to the tool used for
outside turning except that it is ground with less clearance.
To insure accuracy and conserve time, the hole is then finished with a
shell reamer held in the lathe as shown in Fig. 23.
[Illustration: Fig. 23]
=Reaming the Hole.=—Before starting the reamer, the hole should be
bored at the end, for a distance of about ⅛ of an inch, to the size
which will just permit the reamer to enter. This diameter must be
calipered very carefully and should be tested with the reamer itself.
The rest of the hole is then bored about .01 of an inch smaller in
diameter to allow enough material for finishing with the reamer. Since
the reamer used in this case cuts on the sides as well as on the end,
the hole must be bored true to center in order to be reamed true.
If the reamer has a tapered shank, it is held in the lathe by a square
shank socket and wrench, as shown in Fig. 23, and is fed into the work
by turning the hand-crank on the tail-stock.
[Illustration: Fig. 24]
In case the reamer has a straight shank, it is held as shown in Fig.
24. Here a dog is fastened to the end of the reamer and prevented from
turning by a tool clamped at an angle in the tool post. The end of the
tool presses against the dog near the shank of the reamer so that as
the reamer is fed into the work the carriage of the lathe is forced
along with it. This causes the tool to hold the end of the reamer
against the center of the tail-stock.
When reaming work in a lathe, if the tail-stock is off center the hole
will be reamed too large at the front end.
=Accurate Boring with Boring Bar.=—In turning out holes with a boring
bar, if all the cuts are started from one end, that end will be bored
larger than the other. In case the hole is to be reamed, the reamer
will correct this, but if the hole is to be finished with the boring
bar it will be necessary to bore the hole from both ends. This is done
by reversing the feed of the carriage.
=Speed of Lathe.=—The speed of the lathe for reaming should be slower
than when using the boring bar. If the belt is on the second smallest
step of the cone with the back gears in, the lathe should have about
the right speed for reaming. When using the boring bar, the belt should
be on the largest step of the cone without the back gear.
INSIDE THREADING
The inside threads are cut in very much the same manner as the outside
ones. The cutting tool is held in the boring bar and, like all boring
tools, is ground with less clearance than tools used for outside work.
To regulate the depth of each cut, the screw in the adjustable stop is
placed between the stop and the cross-rest. Then by turning the screw
in after a cut has been taken the cross-rest can be drawn back to
permit a deeper cut with the tool.
=Cause of Threads Breaking.=—When cutting threads in cast iron, they
will break if the roughing cuts are too heavy and are liable to if they
are cut to a sharp point. Another cause for the breaking of cast iron
threads is the use of a dull tool, or one with too little clearance.
=Finishing Threads.=—As a general rule cast iron is machined without
using a lubricant, but in finishing threads a little lard oil will aid
in producing a smooth finish.
FINISHING ENDS
The end of the work may be finished by taking a very light cut with
the turning tool and then scraping it with a lathe scraper, as shown
in Fig. 25. To provide a rest for the scraper a tool is clamped in the
tool post and as close as possible to the surface being scraped.
[Illustration: Fig. 25]
[Illustration: Fig. 26]
A scraper is usually made from an old file ground smooth on the two
sides and with a little clearance at the end.
FINISHING TAPER
To finish the taper, set the compound rest at an angle of 30 degrees
with the axis of the lathe. Such a rest is normally at right angles
with the lathe axis so that it must be turned through 60 degrees to cut
the 30 degree angle. A regular turning tool may be used to finish this
angle, but it should be set so that the straight side will be nearly
parallel with the tapered surface.
If the lathe is not provided with a compound rest, the angle may be cut
with the side of a tool set at the proper angle. To set this tool, use
the thread and center gauge, as shown in Fig. 26.
In case the angle is any other than 30, or 60 degrees, it is necessary
to set the tool with a bevel and bevel protractor.
After the taper has been cut, it may be finished smooth by scraping
with a lathe scraper in very much the same manner as shown in Fig. 25.
The tool that is used as a rest is set in as close as possible to the
taper. If this rest is too far away from the surface being finished,
the scraper will chatter leaving a rough surface.
[Illustration: Piece B.
10 Thrds. per 1″ U. S. S.
Rough Casting Fig. 27 Finished Casting
]
DRILLING AND REAMING.
This piece is first placed in the chuck, as shown in Fig. 28, and the
end rough turned to see if it is a good casting. The hole is then
drilled with a ²³⁄₃₂ inch twist drill and reamed out to size with a ¾
inch rose reamer.
[Illustration: Fig. 28]
=Centering Twist Drill.=—This drill will not bore a hole in the center
unless the point is controlled in some way. To do this, a cutting-off
tool is clamped in the tool post with its point well above the center
of the lathe and is then moved close to the point of the drill. As the
drill starts to cut, it wabbles a little on account of the point being
off center. The cutting-off tool is then gradually brought against
the drill which is at the same time being slowly fed into the work by
turning the hand-crank on the tail-stock. It is necessary to have the
drill centered true before it begins to cut the full diameter.
The drill should be placed in the tail-stock so that the cutting edges
are vertical. If they are horizontal, it will be difficult to make the
drill center.
If the hole in this piece were larger, it would be cast with a core and
then machined in the same manner as the 1⅛ inch hole in piece A, but
since it is cast solid, the hole can be machined more advantageously by
using a twist drill and a rose reamer.
=Reaming.=—After the hole has been drilled with the ²³⁄₃₂ drill, bore
it out with a small boring tool for about ⅛ of an inch from the end to
the diameter that will just fit over the reamer and insure its starting
true. Ream the hole with the reamer held in the same manner as the
twist drill in Fig. 28.
=Speed of Lathe.=—The lathe should run slower for reaming than for
drilling. The speed will be about right for this size reamer if the
belt is on the largest step of the cone without the back gears being
used. The speed for the drill may be much faster. With a high-speed
steel drill, the belt can be run on the second smallest step of the
cone. If the drill is made of carbon steel, a slower speed should be
used.
=Advantage of Rose Reamer.=—In drilling long holes like this, the drill
is very apt to get off center a little as it is fed deeper into the
work, even though it may have been started dead true.
The reamer used in this case is called a rose reamer, or rose bit, and
cuts on the end only. For this reason, if the hole is approximately
true, say within ¹⁄₆₄ of an inch, it will ream the hole straight and
true to size if it is once started true.
FINISHING CORNER
After the hole is bored and reamed, the work may be finished at the end
by using a tool ground like a threading tool, but having an angle at
the point a little less than 90 degrees, as in Fig. 29.
[Illustration: Fig. 29]
The boss, or hub, which is 1⅜ inches in diameter, is finished with one
cutting edge of this tool set nearly parallel to the work, the point
being a trifle deeper than the rest. This will insure the full depth of
cut for the entire length and also a good sharp corner. The direction
of feed for this tool should be from the end and towards the square
corner or shoulder. If it is fed in the opposite direction the tool is
apt to chatter.
This tool is also used to finish the end, but it is turned a little
in the tool post so that the other cutting edge is nearly parallel to
the surface to be cut. After using this tool, the work may be finished
smoother by scraping the ends, as in Fig. 25, and by filing the boss,
or hub.
USE OF MANDREL, OR ARBOR
Before this piece can be finished on the outside, it must be forced on
a mandrel, or arbor, and placed in the lathe, as shown in Fig. 30. Most
commercial shops are provided with hardened steel mandrels for this
purpose, but if one is not available it can be made from soft steel in
the following manner:
[Illustration: Fig. 30]
=Making Mandrel.=—Cut off a piece of steel of suitable length, say 6
inches, and rough turn it to within ¹⁄₃₂ of an inch of the diameter of
the hole. Then turn it at the end for a distance of about ⅛ of an inch
to the size that will just fit the hole. The rest of the distance is
now turned .002, or .003 of an inch larger and filed for about 3 inches
until it will just fit the hole. The next 2 inches are filed with a
slight taper so that when the mandrel is pressed into the hole it will
fit tight enough to hold the casting while it is being turned. This
kind of a fit is called a forced, or driving fit.
When making such a mandrel, it is not necessary to turn that portion to
which the dog is fastened.
=Mounting Work on Mandrel.=—Before pressing the mandrel in, it should
be oiled to prevent it from being marred, or scored. Mandrels are
usually forced in with a mandrel press, but if one is not available,
they may be driven in with a hammer. When this method is used, a piece
of lead, or some other soft material, must be held on the end of the
mandrel to keep the hammer from marring the center.
FINISHING OUTSIDE OF PIECE B TO FIT A
This casting is rough turned to within ¹⁄₃₂ of an inch of the finished
size before any part of it is finished. The 1⅛ inch end is then turned
until it fits the corresponding part of the hole in piece A as closely
as possible and yet not so tight that it cannot be freely rotated. This
kind of a fit is called a close running fit.
=Cutting Threads.=—The portion to be threaded should be turned a little
smaller than the diameter at the bottom of the threads in piece A. This
size is measured by means of the inside spring-thread calipers.
There is no recess, or groove, cut at the end of this thread so that
if the threading tool is allowed to travel farther than the end of the
preceding cut, either the point of the tool or the threads may break.
To prevent this, the lathe is stopped when the tool is within a half a
thread of the end and the cut finished by turning the lathe by hand.
In this way the lathe is kept under control and the tool may be drawn
back when it reaches the end of the preceding cut. Experienced lathe
operators do not, as a rule, turn the lathe by hand, but control the
lathe entirely by the shipper.
The speed of the lathe for cutting this thread will be about right for
beginners if the belt is on the second smallest step of the cone and
the back gears are thrown in.
=Finishing the Angle, or Taper.=—The 30 degree angle may be cut by
setting the compound rest to the correct angle and using a regular
turning tool. In case the tool leaves a few tool marks, they may be
removed by filing.
If the lathe is not provided with a compound rest, this angle may be
cut by setting a square-nose tool, as in Fig. 31, with the aid of a
thread gauge. Any other angle would have to be set with a bevel and
bevel protractor.
[Illustration: Fig. 31]
This tool is not as wide as the surface to be cut because one that will
cut the full width is very liable to chatter. It is therefore better to
make several cuts with a narrow tool. The surface can then be finished
smooth by filing.
The closeness of the fit of this taper with that in A can be tested
by rubbing black paint, which consists of lamp black and oil, on the
tapered surface in A. When B is screwed into A, marks will be made on
B indicating the high spots. If these are not too high, they may be
removed by filing.
FINISHING OUTSIDE OF PIECE A.
Piece A may now be screwed on B and the outside rough turned to within
¹⁄₃₂ of an inch of the finished size.
The ends of the different steps are finished to the proper length with
the tool shown in Fig. 29. This same tool can then be used to turn the
different diameters to within 0.002 or 0.003 of an inch of the required
size. These steps are brought to the final size by filing.
=Filing.=—The file for this work should be less than 1 inch in width.
If it is wider than the steps, a beginner will usually file the portion
at the end of each step smaller in diameter than that which is close to
the square corners.
The different diameters may be measured accurately with the micrometer
calipers.
KNURLING
After piece A is finished, it is removed from B and B is reversed in
the lathe so that the boss may be knurled.
In case there is enough room between the dog and the work, when held as
in Fig. 30, there is no need to reverse the work for knurling since it
can be done in this position.
The boss at the end of B is used as a handle so that if it were left
smooth it would be hard to turn by hand. The surface is therefore made
rough with a knurling tool as shown in Fig. 32.
[Illustration: Fig. 32]
The speed of the lathe should be about the same for knurling as for
thread cutting. If the lathe runs too fast, the knurling tool does not
cut satisfactorily.
The tool is set so that the face of the rollers is parallel with the
surface to be knurled. When starting the cut, the rollers can be forced
into the piece easier if about half of their width extends past the end
of the work.
The knurling tool should be pressed into the work fast enough so that
about one half the depth of the finished knurl will be cut while the
lathe makes three or four revolutions. If the tool is forced in too
slow, it will cut a finer knurled surface than the rollers are intended
to cut.
The tool is fed along the surface in the same manner as in plain
turning. The speed at which the carriage of the lathe moves has no
effect upon the pitch of the knurled surface since this is controlled
by the pitch of the grooves in the rollers. If a finer knurled surface
is desired, a knurling tool having rollers with finer grooves would
have to be used.
TRANSCRIBER’S NOTE
Illustrations in this eBook have been positioned between paragraphs
and outside quotations.
Obvious typographical errors and punctuation errors have been
corrected after careful comparison with other occurrences within the
text and consultation of external sources.
Some hyphens in words have been silently removed, some added, when a
predominant preference was found in the original book.
Except for those changes noted below, all misspellings in the text,
and inconsistent or archaic usage, have been retained.
Pg 9: ‘straght’ replaced with ‘straight’
Pg 11: ‘shoull’ replaced with ‘should’
Pg 19: ‘diffrent’ replaced with ‘different.’Project Gutenberg
Elementary lathe practice : $b As adapted to the teaching of machine shop practice in technical schools
Palmateer, T. J. (Theron Josiaha)
Chimera39
High School