Gears are a means of changing the rate of rotation of a machinery shaft. They can also change the direction of the axis of rotation and can change rotary motion to linear motion.

Unfortunately, mechanical engineers sometimes shy away from the use of gears and rely on the advent of electronic controls and the availability of toothed belts, since robust gears for high-speed and/or high-power machinery are often very complex to design. However, for dedicated, high-speed machinery such as an automobile transmission, gears are the optimal medium for low energy loss, high accuracy and low play.

Gears are of several categories, and can be combined in a multitude of ways, some of which are illustrated in the following figures.

Meshing Circular Spur Gears

Rack and Pinion Spur Gears

Circular Worm Gear and Mating Cylindrical Worm

Inside Spur Gear withMating Pinion Spur Gear