Worm gears are often used when large rate reductions are needed. The reduction ratio depends upon the number of starts of the worm and quantity of the teeth on the worm gear. But worm gears possess sliding contact which is noiseless but tends to produce heat and also have relatively low transmission performance.
As for the materials for production, in general, worm is made of hard metal while the worm gear is made from relatively soft metal such as aluminum bronze. This is since the number of teeth on the worm gear is relatively high compared to worm with its number of starts being usually 1 to 4, by reducing the worm equipment hardness, the friction on the worm teeth is reduced. Another feature of worm manufacturing may be the need of specialized machine for gear cutting and tooth grinding of worms. The worm equipment, on the other hand, may be made with the hobbing machine utilized for spur gears. But due to the different tooth shape, it is not possible to cut several gears at once by stacking the apparatus blanks as can be carried out with spur gears.
The applications for worm gears include equipment boxes, fishing pole reels, guitar string tuning pegs, and in which a delicate speed adjustment by utilizing a huge speed reduction is necessary. While you can rotate the worm gear by worm, it is usually extremely hard to rotate worm utilizing the worm gear. That is called the personal locking feature. The self locking feature cannot continually be assured and a separate method is recommended for true positive reverse prevention.
Also there is duplex worm gear type. When using these, it is possible to adapt backlash, as when the teeth wear necessitates backlash adjustment, without requiring a change in the guts distance. There are not too many manufacturers who can produce this kind of worm.
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