Page 439 - Shigley's Mechanical Engineering Design

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414 Mechanical Engineering Design
Table 8–3
5
d, in 4 1 16 3 8 2 1 5 8 3 4 8 7 1 1 1 4 1 1 2 1 3 4 2 2 1 2 3
Preferred Pitches for
1
1
1
1
Acme Threads p, in 16 14 12 10 1 8 1 6 6 1 1 5 5 1 1 4 1 4 4 1 1 3 2 1
are sometimes modified to a stub form by making the teeth shorter. This results in a
larger minor diameter and a somewhat stronger screw.

8–2 The Mechanics of Power Screws

A power screw is a device used in machinery to change angular motion into linear
motion, and, usually, to transmit power. Familiar applications include the lead screws
of lathes, and the screws for vises, presses, and jacks.
An application of power screws to a power-driven jack is shown in Fig. 8–4. You
should be able to identify the worm, the worm gear, the screw, and the nut. Is the
worm gear supported by one bearing or two?

Figure 8–4
The Joyce worm-gear screw
jack. (Courtesy Joyce-Dayton
Corp., Dayton, Ohio.)