What is the standard for gear backlash?

[StCalvin]

3ml~4ml. The existence of gear backlash will cause impact between teeth, affecting the smoothness of gear transmission. Therefore, this gap can only be very small, usually ensured by tooth difference. For gear motion design, it is still designed without gear backlash (zero backlash). Here is some extended information: Design standard: The design criterion for minimum tooth backlash: To ensure the formation of a normal lubricating oil film between tooth surfaces and prevent the teeth from jamming due to thermal expansion deformation caused by the increase in gear working temperature, there must be appropriate tooth backlash when the gears are meshing. The gear backlash is measured using the base tangent length value (there are two values, upper and lower deviations), and the actual tooth thickness value (with corresponding two values) is calculated. Then, the nominal tooth thickness minus the actual tooth thickness gives the difference. Both meshing gears need to be calculated, and the two differences are added together to obtain the gear backlash (two values, minimum backlash and maximum backlash).