Worm Gears This name is used on a #gear assembly consisting of a worm-like screwdriver and a worm #wheel (similar to the ordinary gear).
The #worm #gear is made up of a cylinder wrapped around it teeth can be spiral and may be one tooth or a few teeth and is called the driver gear , while the worm wheel consists of a serrated disc with a relatively large number of teeth and is called driven gear , they are meshed when axes are perpendicular .
Because of the large difference in the number of teeth, worm gears have a very large reduction rate ranging from 1/20 to 1/300 and therefore used in speed reducers .
One of the disadvantages is the large friction between the meshed teeth, so the worm gears are placed in a special case filled with oil .
The direction of transmitted motion is always from the driver gear to the driven gear (from the worm gear to the worm wheel) and the power can not be transmitted in the opposite direction .