When machining the spherical surface, especially the quadrant ball and curved surface, due to improper adjustment, it is easy to produce shoulder, shovel back and so on. The main reasons are:

1. Caused by system clearance

In the equipment transmission pair, there is a certain gap between the lead screw and the nut. With the increase of the equipment operation time, the gap gradually increases due to wear. Therefore, the corresponding gap compensation during reverse movement is the main factor to overcome the shoulder on the machined surface. The clearance measurement usually adopts the dial gauge measurement method, and the error is controlled within 0.01 ~ 0.02mm. It should be pointed out here that the meter base and meter rod should not extend too high or too long, because the cantilever is long during measurement, the meter base is easy to move under force, resulting in inaccurate counting and untrue compensation value.

2. Caused by uneven machining allowance of workpiece

Before realizing the design surface of the part, whether the machining allowance of the surface to be machined is uniform is also an important reason for whether the formed surface can meet the design requirements, because the uneven machining allowance is easy to cause "re mapping" error. Therefore, for parts with high surface shape requirements, the machining allowance shall be as uniform as possible before forming, or one more profile shall be machined to meet the design requirements.

3. Caused by improper tool selection

In cutting, the tool removes material through the main cutting edge. However, after the arc passes through the quadrant and the arc is tangent to the tool auxiliary cutting edge (the intersection line between the rear of the auxiliary cutting edge and the base surface), the auxiliary cutting edge may participate in cutting (i.e. shovel back). Therefore, the wedge angle of the tool must be considered when selecting or grinding the tool.