The Hand of a Worm

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The hand of a worm
Worm gears are manufactured with right or left-hand threads and teeth. The hand of a worm or worm gear may be determined by noting the direction in which the threads or teeth lean when the worm or worm gear is held with the hole facing up. (See Figure 4.4)

In a worm gear set, the worm and gear must have the same hand, pitch, number of threads, and tooth dimensions. They also must have the same pressure angle and lead angle (terms you will learn about below).

Reminder: Right hand worm and worm gear sets are considered standard. As a result, right-hand sets will always be furnished unless otherwise specified.

The lead of a worm is the distance any one thread advances in a single revolution. The lead may be calculated using either one of the following formulas:
• Lead = (Number of worm threads x 3.1416) ÷ diametral pitch
• Lead = Circular pitch x number of worm threads

The following information also will come in handy when determining the lead of a worm:
• The lead and circular (linear) pitch are equal on single-thread worms.
• The lead is twice the circular pitch on double-thread worms.
• The lead is three times the circular pitch on triple-thread worms.
• The lead is four times the circular pitch on quadruple-thread worms.

The lead angle of a worm is the angle formed by the worm thread and a line perpendicular to the worm axis. (See Figure 4.5)