Gears are machine elements, which are used for power transmission between shafts, separated by small distance. Irrespective of the type, each gear is provided with projections called teeth and intermediate depressions called tooth spaces. While two gears are meshing, the teeth of one gear enter the spaces of the other. Thus, the drive is positive and when one gear rotates, the other also rotates; transmitting power from one shaft to the other.
Gears are classified on the basis of the shape of the tooth profile and the relative position of the shafts between which, power transmission takes place. The pictorial views of some of the most commonly used gear trains, are shown in Fig.
