What is the allowable error in gear module

The modulus pressure angle and helix angle determine the pitch of the base circle, and adding the number of teeth determines the size of the base circle. The size of the base circle determines the shape of the involute. To understand the definition of modulus, it is actually a parameter that is close to a coefficient and cannot be directly measured by physical means.

M=p/π
m: Module p: pitch (theoretically measurable physical quantity), so what we actually measure is the error of the involute tooth surface, and module is one of the determining factors.

There are many parameters for measuring the involute tooth surface error of gears, and now the mainstream measurement in factories is the tooth profile direction error F α， Tooth direction error F β， Individual tooth pitch error fpt, cumulative tooth pitch Fp, tooth jump Fr. F α， F β It is the error value obtained by comparing the actual object with the theoretical shape in both tooth shape and tooth direction. It controls the shape of the involute tooth surface. FPT is the pitch error between adjacent teeth, which can be equivalently considered as the measurement of modulus error. But it will also be affected by the concentricity of the gear positioning center and the center of the indexing circle (although this influence will be relatively small). Fp is the difference between the maximum and minimum values of all fpts, which is generally measured by the concentricity of the involute indexing circle center and the gear inner hole or positioning (with relatively small modulus errors).

Fr is a fast detection method for Fp, generally used for measurement on production lines and does not require submission to the testing department. So F α， F β Controlled the tooth surface error on the teeth, fpt controlled the position error of each tooth after the array, and Fp controlled the error between the tooth surface center and positioning. Only gears that pass the above tests are considered qualified. These numerical ISO standards provide levels of 1-12. Different processing methods and working conditions can choose different accuracy levels. It is generally believed that as long as the accuracy requirements are met, it does not affect the gear meshing effect.