Not only when the gear precision is not enough, the wear is too fast to reduce the life span greatly, the gear is not in place when the teeth are running. The base section error and tooth shape error are too large, the backlash is too large, and the surface roughness is large. Gear train and gearbox Assembly eccentricity, low contact accuracy, shaft parallelism, shaft, bearing, support stiffness and so on. For the surface roughness of gear tooth surface generally take 1.6, if the requirement of grinding teeth, such as high precision processing, roughness can be 0.8 or smaller. For the tooth top round surface, generally takes 6.3, but for the tooth top circle as the Test datum (for example, the tooth chord thickness), that will be smaller, take at least 3.2 or smaller.