In their most essential form, gears are round, toothed devices enabling the conversion of engine speed into torque. Gears are either mounted to, or are a part of, a gear shaft. Many of the more common gears will have a hole in the center, known as a bore, through which the gear shaft is fitted. When the gear shaft is rotated, the gear also rotates.
Essentially, the gear shaft is the axle of the gear, providing the rotation that allows one gear to engage with and turn another. The process is often known as gear reduction and is essential to transferring horsepower from engine to drive mechanism. The conversion of engine speed into torque is what provides the driving force powering, for example, the wheels of an automobile. Through the gears and shafts in an automobile transmission, the engine is able to run at a constant speed, while the auto wheels can be run faster or slower, or even in reverse, using the same engine rotational direction and speed.
The flywheel of the ordinary automobile engine is connected to a gear shaft mounting a number of different-sized gears. Through horizontal movement of the shaft, these main gears are engaged with, and disengaged from other larger and smaller gears, also mounted on gear shafts. As well, the drive shaft, which delivers power from the gearing in an automobile transmission to the axle and on to the drive wheels, is one very common example of a gear shaft.
Gear shafts may, as well, contain gear teeth integrated into the shaft, thus becoming a shaft gear. Such shafts with gearing at each end are called intersecting shaft gears. Bevel gears and spiral gears are intersecting shaft gears. A good example of this type of gearing is a helicopter rotor. A vertical intersecting shaft gear from the engine engages one or more horizontal shaft gears to turn the rotors.
The identical principle applies for an automobile. The drive shaft is often a shaft at the transmission end, and an intersecting shaft gear at the differential end. This configuration allows vertical movement to be converted into horizontal movement.
Some different types of gear shafts are eccentric shafts, coupling-gear shafts, splined shafts, and keyed shafts. Gears used in a heavy duty application will most likely be manufactured of a sturdy metal. Other materials used to manufacture these shafts are copper aluminum and plastic. The original gear shaft, commonly found with the medieval grinding wheel, was made of wood.
