Some Factors to Keep in Mind in Gear Design

Gear DesignSometimes in gear design (for e.g. in the case of spur gears, i.e. driver and driven) gears are to be designed for a specific velocity ratio and distance between central shafts. For the purpose of understanding this gear design better, let:

x = Distance between the centres of two shafts
N1 = Speed of the driver
T1 = Number of teeth on the driver
d1 = Pitch circle diameter of the driver
N2 T2 and d2 = Corresponding values for the driven or follower, and
Pc = Circular pitch

We know that the distance between the centres of two shafts,

x = (d1 + d2)/2

and speed ratio or velocity ratio,
N1/N2 = d2/d1 = T2/T1

From the above equations, we can calculate d1 and d2 (or T1 and T2) and the circular pitch (Pc). The values of T1 and T2 as obtained above, may or may not be whole numbers. But in gear design, since the number of teeth is always a whole number, a slight alteration must be made in the values of x, d1, and d2, so that number of teeth in the gear design is a complete number.