Lathes Page: 2
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TM 1-420
TECHNICAL MANUAL C 1
42. Lathe thread-cutting mechanism.
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. * * *
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(2) As an example in the use of compound gearing * * * nu-
merator and denominator are both multiplied by 4:
4 4 16
X-
48 4 192
In simple gearing the driving gear would have 16 teeth and the driven
gear 192 teeth; however, 192 teeth is far greater than the available
tooth range. For use in compound gearing the fraction 4%3 is changed
to any two components whose product is equal to 4%; for example:
* * * * * * *
f. In any thread-cutting operation it is necessary to place the
locking device in a neutral position in order to close the split nut
on the lead screw to cause the carriage to travel at threading speed.
Since the lead screw can be caused to revolve either clockwise or
counterclockwise by means of a reversing gear or lever, it is also nec-
essary to see that the lead screw turns in the proper direction.
[A. G. 062.11 (1-7-42).] (C 1, Mar. 10, 1942.)
43. Cutting 60 threads.--a. * * *
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(2) The 600 center gage (fig. 63) * * * tool were made to
correspond exactly to the gage. It is therefore necessary to make
the roughing tool angle 1/20 to 1/40 less than the gage angle, while the
finishing tool bit angle should be 10 to 3 less than the gage angle.
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(5) Since the compound rest is set at an angle to the ways of the
lathe and the advance for each cut is made with the compound, the
tool will cut only on one side of the thread groove as it is advanced
for each successive cut. This enables the tool to have side rake,
allowing faster cutting and producing better finishes. Furthermore,
if a tool is advanced so that both sides cut at the same time, there
may be a gouging or tearing action which must be avoided as much as
possible in threading. It will also be best to decrease the depth of
cut as the tool goes deeper into the work to reduce further this
tearing tendency. At any time that a bur is seen forming at the top
of the thread, a file should be used to break it down. Figure 64 illus-
trates the proper method of feeding a 60 tool bit.
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United States. Army. Air Corps. Lathes, book, November 29, 1940; Washington, D.C.. (https://digital.library.unt.edu/ark:/67531/metadc96655/m1/103/: accessed March 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.