Lathes Page: 69
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formula will allow the operator to determine the number of teeth
required in the sector replacement gear:
Where: A =number of teeth in stud gear.
B = number of threads per inch to be cut.
C= nearest number to B on index plate.
X=number of teeth in replacement sector gear.
As an example in the use of this formula, let it be assumed that 27
threads per inch are to be cut on a lathe having a 48 tooth stud gear
and a 48 tooth sector:
With the feed box handle in 24 thread position and the 54 tooth gear
on the sector, the lathe will cut 27 threads per inch.
FIGURE 62.-Position of threading tool.
f. In any thread-cutting operation it is necessary to place the feed
reversing lever in neutral 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 counter-
clockwise by means of a reversing gear or lever, it is also necessary
to see that the lead screw turns in the proper direction.
43. Cutting 600 threads.-a. In cutting all 600 threads the com-
pound rest is carefully set at a 300 angle and its slides adjusted, as
any lost motion at this point may cause considerable trouble during
the threading operation. If the work is to be held between centers,
the centers must be clean, freshly oiled, and adjusted so there is no
end play. Unless otherwise specified, the end of the thread should be
chamfered by cutting either a 450 angle or a radius larger than the
depth of the thread.
(1) Much depends on the careful preparation of the cutting tool
for thread cutting. It must be sharp, smooth, and properly shaped
to obtain good results. It is often considered good practice to grind
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United States. Army. Air Corps. Lathes, book, November 29, 1940; Washington, D.C.. (digital.library.unt.edu/ark:/67531/metadc96655/m1/71/: accessed February 27, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.