Machine Drawing

Chains and Gears 191

dharm
d:\N-Design\Des13-1.pm5

R

(a) (b)

Fig. 13.3 Sprockets

13.7 Gears

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.

13.8 Types of Gears

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. 13.4.

Spur Helical

Bevel

Worm and

worm gear

Rack and pinion

Fig. 13.4 Types of gears

13.9 Gear Nomenclature

Figure 13.5a shows the parts of a spur gear and Fig. 13.5b, two spur gears in mesh; indicating

all the terms associated with the gearing. These terms are also applicable to all types of gears.