Worm gear arrangement jack project full detail

A worm gear is a gear arrangement in which a screw (which is a screw-shaped gear) engages with an endless gear (which is similar in appearance to a straight gear). The two elements are also called worm and worm wheel. The terminology is often confused with the imprecise use of the term worm gear to refer to the worm, the worm gear or the worm mechanism as a unit.
Like other gear arrangements, a worm mechanism can reduce the speed of rotation or transmit a higher torque. A worm is an example of a screw, one of six simple machines.

A gearbox designed with a worm screw and a worm wheel is considerably smaller than one made of flat straight gears and has its drive shafts at 90 ° from each other. With a single starter worm, for each 360 ° rotation of the worm, the worm gear advances only one cog of the gear. Therefore, regardless of the size of the worm (without prejudice to sensitive engineering limits), the ratio of gears is the "size of the worm gear to 1". Given a single starting worm, a 20-tooth tooth gear reduces the speed in the ratio of 20: 1. With straight gears, a 12-tooth gear must match with a 240-tooth gear to achieve the same 20: 1. Therefore, if the diametral pitch (DP) of each gear is the same, then, in terms of the physical size of the 240-tooth gear to that of the 20-tooth gear, the worm gear is considerably smaller in volume.

Unlike ordinary gear trains, the transmission direction (input shaft vs. output shaft) is not reversible when large reduction ratios are used, due to the greater friction between the worm and the worm wheel, when usually a single Worm boot It is used. This can be an advantage when it is desired to eliminate any possibility of the output pushing the input. If a multi-segment worm (multiple spirals) is used, then the ratio is reduced accordingly and the braking effect of a worm and worm gear may have to be discounted, since the gear may be able to drive the worm.
Helical gear configurations in which the gear can not operate the worm are called self-locking. The fact that a worm and a gear is self-locking depends on the feed angle, pressure angle and coefficient of friction.