Figure 6-91.--Compound rest set at 29 1/2°.
placing the levers as indicated on the index plate for
the thread desired.
When you have the lathe set up to control the
carriage movement for cutting the desired thread
Ordinarily on threads of fine lead, you feed the
pitch, your next consideration is shaping the thread.
tool straight into the work in successive cuts. For
Grind the cutting tool to the shape required for the
coarse threads, it is better to set the compound rest at
form of the thread to be cut, that is-V-form, Acme,
one-half of the included angle of the thread and feed
square, and so on.
in along the side of the thread. For the last few
finishing cuts, you should feed the tool straight in
Mounting Work in the Lathe
with the cross-feed of the lathe to make a smooth,
even finish on both sides of the thread.
When you mount work between lathe centers for
cutting screw threads, be sure the lathe dog is securely
In cutting V-form threads and when maximum
attached before you start to cut the thread. If the dog
production is desired, it is customary to place the
should slip, the thread will be ruined. Do not remove
compound rest of the lathe at an angle of 29 1/2°, as
the lathe dog from the work until you have completed
the thread. If you must remove the work from the
compound rest in this position and use the compound
lathe before the thread is completed, be sure to replace
the lathe dog in the same slot of the driving plate.
rest screw to adjust the depth of cut, you remove most
of the metal by using the left side of the threading tool
When you thread work in the lathe chuck, be sure
the chuck jaws are tight and the work is well
the way better than if you feed the tool straight in, and
supported. Never remove the work from the chuck
keeps the thread from tearing. Since the angle on the
until the thread is finished.
side of the threading tool is 30°, the right side of the
tool will shave the thread smooth and produce a better
When you thread long slender shafts, use a
finish; although it does not remove enough metal to
follower rest. You must use the center rest to support
interfere with the main chip, which is taken by the left
one end of long work that is to be threaded on the
side of the tool.