Selection of modulus and number of teeth in gear design

1. According to the magnitude of external load, preliminarily estimate the module m of the gear. If a helical gear is selected, please select an appropriate helix angle. Then speed up the transmission according to the speed ratio (for example, the input speed is 4rpm and the output speed is 8rpm) as 1/2, so that the transmission ratio of the two gears is Z 1/Z2=2: 1. Then Z 1 and Z2 can be obtained from the intermediate principal distance a=m(Z 1+Z2). If it is a helical gear, a=m(Z 1+Z2)/cos (helix angle).

2. Next, when the gear pressure angle is 20 degrees, the tooth top height coefficient is 1, and the tooth root height coefficient is 1.25, the gear parameters can be basically obtained.

Gears should be designed, not chosen. The type is related to the arrangement of shafts. Cylindrical gears are used for parallel shafts and bevel gears are used for intersecting shafts. The minimum number of teeth of spur gear is 17, and less than this number should be undercut. Modulus is calculated by bending strength, and pitting resistance is calculated by contact strength.