Mechanical drives are accustomed to transmit motion, torque and power from a driver shaft to driven shaft. The driver shaft, in majority of the cases, is a part of primary mover (such as for example electric engine, hydraulic turbine, steam turbine, etc.); while, the powered shaft is part of the machine unit. There exist four basic mechanical drives, namely gear drive, belt drive, chain drive and rope drive. A equipment drive is 1 engagement type rigid drive where motion and power are transmitted by way of successive engagement and disengagement of tooth of two mating gears. It really is inherently free from slip and this it offers constant velocity ratio (positive drive). It can be used for light duty applications (such as for example toys, watches, etc.) aswell as for heavy duty applications (such as for example gear container of machinery, marine drive, etc.).

Driver and driven shafts might have 3 mutual orientations, namely (we) parallel shafts, (ii) intersecting shafts and (iii) nonparallel nonintersecting shafts. There can be found four fundamental types of gears and the right gear should be selected based on the mutual orientation of the driver and powered shafts. Spur equipment and helical gear are applicable for parallel shafts. Bevel gear can be applied for two intersecting shafts, which may not necessarily be perpendicular. Worm gear arrangement is used for the 3rd category (nonparallel non-intersecting shafts). Unlike spur gears which have straight the teeth parallel to the apparatus axis, helical gears have teeth in helical form that are cut on the pitch cylinder. Although helical gears are commonly utilized for parallel shafts like spur gears, it may also be utilized for perpendicular but non-intersecting shafts.

Accordingly presently there are two types of helical gears-parallel and crossed. Parallel helical gears, the normal one, can be used to for power transmission between parallel shafts. Two mating parallel helical gears must have same module, same pressure angle but opposite hands of helix. They provide vibration-free and quiet procedure and may transmit heavy load. On the other hand, crossed helical gears are used for nonintersecting but perpendicular shafts. Two mating crossed helical gears (also known as screw gears) must have same module, same pressure position and either same or opposite hand of helix. This type of gear has software similar to worm gear; however, worm equipment is favored for steep speed reduction (1:15 to at least one 1:100), whereas crossed helical gears cannot offer quickness reduction beyond 1:2. Various differences between parallel helical gear and crossed helical gear are given below in desk format.