A bevel gear is a gear which is designed to connect with a gear mounted on an axis which may be positioned at any number of angles. Classically, bevel gears are used at 90 degree angles to each other, although other types of angles may be used as well. This is by contrast with other types of gears, which must generally be used either parallel to each other, or at right angles, in some specialized cases. Bevel gears are used in a number of applications, including the differential gear of a car.
As the term “bevel” would suggest, the face of a bevel gear is angled. Typically, a bevel gear is conical in shape, with the teeth running along the side of the cone, and the angle of the sides can be varied, depending on the application for the gear. The beveled design allows the gear to intermesh with another bevel gear at several different angles, depending on how it has been machined.
In a straight bevel gear, the teeth are straight, running vertically along the cone. The problem with straight toothed gears is that all of the impact comes down on a single tooth, making the gear rather rough, and leading to chipping along the teeth of the gear over time. For this reason, some people prefer spiral gears, in which the teeth are set at an angle, allowing the pressure to be distributed so that the gears mesh evenly and smoothly. Spiral bevel gears are readily available for a range of tasks.
Hypoid bevel gears are specialized bevel gears with axes which do not intersect. These gears utilize a large ring gear with a smaller meshing gear, and they are used in applications like car differentials, in which it may be necessary for gears to turn at different rates of speed in some situations. Hypoid gears require custom lubricants, because they are often subjected to a significant amount of strain.
One example of a bevel gear can be found in the workings of many garage doors. The gears used to turn the door are often set at right angles to each other, as can be seen upon close examination. Bevel gears are also used in other types of doors and gates, such as sluice gates for dams which are often operated by a user's manipulation of a screw which turns a bevel gear to open or close the gate.