![]() ![]() In order to minimize friction (and therefore, heat), the worm and gear are made of dissimilar metals – for example, the worm may be made of hardened steel and the gear made of bronze or aluminum.Īlthough the sliding contact reduces efficiency, it provides very quiet operation. This sliding action causes friction and heat, which limits the efficiency of worm gears to 30 to 50 percent. ![]() The meshing of the worm and the gear is a mixture of sliding and rolling actions, but sliding contact dominates at high reduction ratios. Image credit: Kohara Gear Industry Company, Ltd. (This is different from most other types of gears, where the gear reduction is a function of the diameters of the two components.) The worm in a worm gear assembly can have one start (thread) or multiple starts. For a multi-start worm, the gear reduction equals the number of teeth on the gear, divided by the number of starts on the worm. So a gear with 24 teeth will provide a gear reduction of 24:1. For a single-start worm, each full turn (360 degrees) of the worm advances the gear by one tooth. Like a ball screw, the worm in a worm gear may have a single start or multiple starts – meaning that there are multiple threads, or helicies, on the worm. The worm is typically the driving component, with the worm’s thread advancing the teeth of the gear. The worm is analogous to a screw with a V-type thread, and the gear is analogous to a spur gear. Worm gears are constructed of a worm and a gear (sometimes referred to as a worm wheel), with non-parallel, non-intersecting shafts oriented 90 degrees to each other. Although their efficiency is relatively low, they can provide very high reduction ratios and, in many cases, are self-locking. Worm gears are found in industrial applications, heavy equipment, and even consumer applications.
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