In the machining of precision parts, the main reasons for the surface roughness can be summarized into two aspects: one is the surface roughness formed by the relative motion trajectory of the cutting edge and the workpiece (geometric factors); the other is the factors related to the nature of the processed material and the cutting mechanism (Physical factors). In cutting, the geometric factors that cause surface roughness are the residual area of ​​the cutting and the quality of the cutting edge sharpening. The greater the height of the residual area, the rougher the surface. According to the cutting principle, the height of the residual area is related to the feed rate, the arc radius of the tool tip and the main and secondary deflection angles of the tool. The physical factors that affect the surface quality are plastic deformation, friction, built-up edge, scale spurs and high-frequency vibration in the process system during the cutting process. In order to control the surface roughness value in precision parts processing, the following measures can be taken: 1. Because it is easy to produce built-up tumor scales within a certain cutting speed range, it is necessary to choose a reasonable cutting speed and generally avoid medium-speed cutting. For example, when turning 45 steel, when the cutting speed exceeds 100m/min, the surface roughness value decreases to stabilize. Choosing a small feed rate can reduce the height of the residual area, thereby reducing the surface roughness value. 2. Reasonable selection of tool materials and geometric parameters. When the affinity between the tool material and the material being processed is large, it will cause accelerated wear of the tool and affect the surface roughness of the workpiece. The geometric parameters of the tool include the geometric angle of the tool, the form of the blade and the shape of the cutting edge, which have the most direct impact on the surface roughness of the part. The selection must be based on the material of the part, the material of the tool and the nature of the processing. 3. Cutting fluid has a significant effect on the surface roughness of precision parts. The cooling effect of the cutting fluid reduces the cutting temperature, and the lubrication effect of the cutting fluid improves the friction between the tool and the machined surface, thereby reducing the plastic deformation of the cutting process and inhibiting the growth of built-up tumors and scales, which reduces the surface Roughness plays a big role.