Lathes Page: 89
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56. Worm gears.-a. Worm gears are used to connect shafts
which are perpendicular to each other and where a great reduction
of speed is required with a corresponding increase in power. A pair
of worm gears consists of a worm, made similarly to a screw, whose
threads mesh with the teeth of a gear called a worm wheel (fig. 79).
OVT5OE ThROAT ______.
DIAMETER DIAMETE R -a AMET-R AJOR.
Fl RE 7. Worm1 and w orm wheel nomenclature.
b. The complete worm is machined in the lathe, including the cutting
of the Brown and Sharpe 29 worm thread. The commonly used
Pitch diameter = 2.4 x linear pitch + 1.1.
Outside diameter= 3.036 x linear pitch + 1.1.
Minor diameter= 1.664 x linear pitch+ 1.1.
c. Worms may be double or triple threaded to increase the speed
without decreasing the center distance.
d. The worm wheel blank is machined in the lathe, and the teeth
are gashed and hobbed in the milling machine.
(1) As shown in figure 79, the throat diameter of a worm wheel
is measured at the center of the concave face, and the outside diameter
is measured over the corners.
(2) The throat curvature may be machined by the use of a radius
forming tool or by turning free hand and fitting to a template.
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United States. Army. Air Corps. Lathes, book, November 29, 1940; Washington, D.C.. (digital.library.unt.edu/ark:/67531/metadc96655/m1/91/: accessed July 26, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.