Lathes Page: 81

TVM 1-420
LATHES 47
The lathe is set to cut four threads per inch and the thread is cut to
the depth of a standard eight pitch thread. Another thread of like
depth is then cut on the screw, halfway between the spirals of the
first thread, resulting in a thread of eight pitch but having 1/4-inch
lead. The triple pitch thread requires three spiral grooves to be cut
around the screw in a similar manner, while the quadruple thread
requires four grooves, etc.
I
I 1
I TI40EAD OCCUM-
I RENCE AT THE.Toot.. -r
M,0 OI M.TER+
I ANGLE OF THREAD
FlortE 74.--(aleulation for thread helix angle.
b. One of the major requirements of multiple threads is the equal
spacing of the grooves and may be accomplished in any of the follow-
ing ways:
(1) By the use of the thread chasing dial.
(2) By setting the compound rest parallel to the ways of the lathe,
so that after the first pitch has been cut the micrometer dial of the
compound may be moved the exact number of thousandths for the
next pitch.
(3) By the use of a driving plate having the proper number of
accurately spaced slots to accommodate the tail of the driving dog.
After one pitch is cut, the tail of the dog is simply shifted to the
next slot, etc.

81

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United States. Army. Air Corps. Lathes, book, November 29, 1940; Washington, D.C.. (digital.library.unt.edu/ark:/67531/metadc96655/m1/83/ocr/: accessed March 27, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.