# Simple Gear Selection Procedure

Simple Gear Selection Procedure

The Lewis formula, in the form given by $\sigma&space;=\frac{W_{t}}{FmY}$  can be used in a provisional spur gear selection procedure for a given transmission power, input, and output speeds. The procedure is outlined as follows:

1. Select the number of teeth for the pinion and the gear to give the required gear ratio. Note that the minimum number of teeth permissible when using a pressure angle of 20° is 18.
2. Use either the standard teeth numbers or as listed in a stock gear catalog.
3. Select a material. This will be limited to those listed in the stock gear catalogs.
4. Select a module, m from standard or as listed in a stock gear catalog
5. Calculate the pitch diameter, d = mN.
6. Calculate the pitch line velocity, $V=(d/2)\times&space;n\times&space;(2\pi&space;/60)$
7. Calculate the dynamic factor, $K_{v}=6.1/6.1+V$
8. Calculate the transmitted load, Wt = Power/V.
9. Calculate an acceptable face width using the Lewis formula in the form $F&space;=\frac{W_{t}}{K_{v}mY\sigma&space;_{p}}$

References:

CHILDS, PETER R. N. MECHANICAL DESIGN ENGINEERING HANDBOOK. BUTTERWORTH-HEINEMANN LTD, 2014.