Designing of the shafts and spur gear

MACHINE DRIVE

GEAR DRIVE

Introduction:

Designing of the shafts include calculation of the diameter of the shaft.

Design procedure:

In order to find the diameter of shaft for spur gears, the following procedure may be followed.

1. First of all, find the normal load (WN), acting between the tooth surfaces. It is given by

W_N = W_T / cos φ
where W_T = Tangential load,

 and φ = Pressure angle.
A thrust parallel and equal to WN will act at the gear centre.


2. The weight of the gear is given by

W_G = 0.001 18 T_G.b.m²(in N)
where T_G = No. of teeth on the gear,
b = Face width in mm, and
m = Module in mm.

3. Now the resultant load acting on the gear,
    


 Load acting on the gear

4. If the gear is overhung on the shaft, then bending moment on the shaft due to the resultant load
M = WR × x
where x = Overhang i.e. the distance between the centre of gear and the centre of bearing.

5. Since the shaft is under the combined effect of torsion and bending, therefore we shall determine the equivalent torque. We know that equivalent torque


where T = Twisting moment = W_T × D_G / 2

6. Now the diameter of the gear shaft (d ) is determined by using the following relation, i.e.


where τ = Shear stress for the material of the gear shaft.

Note : Proceeding in the similar way as discussed above, we may calculate the diameter of the pinion shaft.