Worm Gears

A worm and worm gear set (Figure 15) is essentially a screw meshing with a special helical gear. Like a screw, the worm can have one or more threads. Two things immediately characterise worm gearing, namely large velocity ratios (up to 300 or more) and high sliding velocities. The high sliding velocities mean that heat generation and power transmission efficiency are of greater concern than with other types of gears.

Figure 15 Single start worm gear. (Marshek)	Figure 16 Double start worm gear. (Marshek)