worm wheel

Worm gears are usually used when large speed reductions are needed. The decrease ratio is determined by the number of starts of the worm and amount of teeth on the worm gear. But worm gears have sliding contact which is noiseless but will produce heat and have relatively low transmission effectiveness.
For the materials for production, in general, worm is constructed of hard metal while the worm gear is manufactured out of relatively soft metal such as aluminum bronze. This is because the number of the teeth on the worm gear is relatively high compared to worm using its number of starts being generally 1 to 4, by reducing the worm equipment hardness, the friction on the worm tooth is reduced. Another worm wheel feature of worm manufacturing is the need of specialized machine for gear slicing and tooth grinding of worms. The worm equipment, however, may be made with the hobbing machine utilized for spur gears. But because of the various tooth shape, it is not possible to cut a number of gears simultaneously by stacking the gear blanks as can be carried out with spur gears.
The applications for worm gears include gear boxes, fishing pole reels, guitar string tuning pegs, and where a delicate velocity adjustment by utilizing a big speed reduction is needed. When you can rotate the worm gear by worm, it is normally not possible to rotate worm utilizing the worm gear. This is called the self locking feature. The self locking feature cannot always be assured and a separate method is preferred for true positive reverse prevention.