Mechanical drives are used to transmit motion, torque and power from a driver shaft to powered shaft. The driver shaft, in majority of the cases, is a part of prime mover (such as electric electric motor, hydraulic turbine, steam turbine, etc.); while, the driven shaft is part of the machine device. There exist four fundamental 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 the teeth of two mating gears. It is inherently free from slip and this it provides continuous velocity ratio (positive drive). It can be used for light duty applications (such as for example toys, watches, etc.) as well as for heavy duty applications (such as for example gear box 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 exist four basic types of gears and a suitable gear should be selected based on the mutual orientation of the driver and driven shafts. Spur equipment and helical gear can be applied for parallel shafts. Bevel equipment can be requested two intersecting shafts, which might not necessarily be perpendicular. Worm gear arrangement can be used for the third category (nonparallel nonintersecting shafts). Unlike spur gears which have straight tooth parallel to the apparatus axis, helical gears possess teeth in helical form that are cut on the pitch cylinder. Although helical gears are generally used for parallel shafts like spur gears, it can also be utilized for perpendicular but non-intersecting shafts.
Accordingly there are two types of helical gears-parallel and crossed. Parallel helical gears, the common one, is used to for power transmitting between parallel shafts. Two mating parallel helical gears must have same module, same pressure position but opposite hands of helix. They offer vibration-free and quiet operation and may transmit heavy load. However, 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 hands of helix. This type of gear has program similar to worm gear; however, worm gear is favored for steep speed decrease (1:15 to 1 1:100), whereas crossed helical gears cannot offer quickness reduction beyond 1:2. Various differences between parallel helical gear and crossed helical equipment are given below in desk format.