Face gears — also known as crown gears —are angular gear systems, and typically consist of a grooved, disk-shaped gear combined with a spur, helical, or conical pinion. A face gear has a planar pitch surface and a planar root surface, and both surfaces are perpendicular to the axis of rotation.
Although face gears have been in use since ancient times, they are not as widely used as other gear types in angle drives, such as bevel and worm drives. This was mainly because calculations required in their manufacture were highly complex. In addition, bevel gears were a reasonable alternative, could transmit more power, and were easier to manufacture. However, a growing acknowledgement of the special advantages of face gears, together with developments in computer-aided computational methods and manufacturing, have resulted in a renewed interest and use of these gears.
The main advantage of face gears is the axial freedom of the pinion. This makes these gears particularly useful in applications that require low backlash, such as in robot drives or low antennae drives. They are also useful in extremely lightly built drives, since the contact position is not significantly influenced, resulting in very little deformations to the housing. Hence they are widely used in the helicopter industry. Many applications of these gears are now used in the automotive industry as well, from low power drives such as mirror actuators and windshield wiper systems, to high power drives such as rear axle drives.