generally limited to use at linear speeds less than 1000 feet/min; or, for small gears, under 1000 rpm. Zerol tooth lines Zerol bevel gears are an intermediate type between straight and spiral bevel gears. Their teeth are curved, but not angled. Zerol bevel gears are designed with the intent of duplicating the characteristics of a straight bevel gear, but they are produced using a spiral bevel cutting process. Manufacturing bevel gears Materials used in gear manufacturing process Bevel gearing Applications The bevel gear has many diverse applications such as locomotives, marine applications, automobiles, printing presses, cooling towers, power plants, steel plants, railway track inspection machines, etc. For examples, see the following articles on: Bevel gears are used in differential drives, which can transmit power to two axles spinning at different speeds, such as those on a cornering automobile. Bevel gears are used as the main mechanism for a hand drill. As the handle of the drill is turned in a vertical direction, the bevel gears change the rotation of the chuck to a horizontal rotation. The bevel gears in a hand drill have the added advantage of increasing the speed of rotation of the chuck and this makes it possible to drill a range of materials. Spiral bevel gears are important components on rotorcraft drive systems. These components are required to operate at high speeds, high loads, and for a large number of load cycles. In this application, spiral bevel gears are used to redirect the shaft from the horizontal gas turbine engine to the vertical rotor. Bevel gears are also used as speed reducers Advantages This gear makes it possible to change the operating angle. Differing of the number of teeth (effectively diameter) on each wheel allows mechanical advantage to be changed. By increasing or decreasing the ratio of teeth between the drive and driven wheels one may change the ratio of rotations between the two, meaning that the rotational drive and torque of the second wheel can be changed in relation to the first, with speed increasing and torque decreasing, or speed decreasing and torque increasing. Disadvantages One wheel of such gear is designed to work with its complementary wheel and no other. Must be precisely mounted. The shafts' bearings must be capable of supporting significant forces. See also Crown gear Pitch cone Front cone Back cone References External links Gears ja:歯車#かさ歯車 pt:Engrenagem