Bevel gears look different from ordinary gears. This special type of gears can be distinguished from the ordinary or spur gears by looking at the axes of the two shafts as well as the shape of the tooth-bearing faces. The axes of the two shafts in a bevel gear intersect while those of an ordinary spur gear are parallel to each other. Often, bevel gears are mounted of shafts that are at right angles to each other but they can be made to work for other angles as well.
There are several types of bevel gears, namely straight, spiral, zerol and hypoid. These are classified according to their geometry. Straight bevel gears have conical pitch surfaces and straight teeth that narrow toward the apex. Spiral bevel gears allow a smooth and gradual contact due to its teeth which are curved at an angle. Zerol bevel gears are spiral bevel gears that have their teeth curved at an angle of zero. Lastly, hypoid bevel gears are spiral bevel gears that have hyperbolic pitch surfaces rather than conical.
Mainly used for changing the direction of rotation by 90 degrees, bevel gears have a lot of applications. Usefulness of the bevel gear is displayed in its uses in various industrial purposes. They can be used for different types of machinery including locomotives, automobiles, printing presses, marine applications, electrical equipment and railway tracks among others.
The hand drill is probably the most common example of the use of a bevel gear. The bevel gear allows the direction of rotation to be changed. As the handle is turned vertically, the bevel gear changes the direction of the chuck to a horizontal direction. The bevel gear also adds the advantage of increasing the rotation speed allowing the possibility of drilling a wide range of materials.
Bevel gears are also used in differential drives. Differentials are devices found in automobiles. They allow the wheels of an automobile to rotate at different speeds. This is important when turning corners as the inner wheel needs to travel a shorter distance. Without differentials, the inner wheel might spin or the outer wheel might be dragged which may result to a strained or unpredictable handling of the vehicle as well as damage to the tires or roads.
Planers are metalworking machine tools analogous to shapers that utilize a linear motion between the cutting tool and the work piece. They also make use of bevel gears. Bevel gears in these machines allow minor adjustments during assembly. They permit displacement due to deflection under operation loads.