In CNC numerical control machining, often people mention the surface finish of the workpiece and surface roughness requirements, in fact, these two calls are the same concept, the surface finish is according to the human vision, the point of view put forward, while the surface roughness is according to the surface micro-geometry of the actual put forward. Because of the international standard (SO) convergence, China adopted the surface roughness after the 80's and abolished the surface finish. In the surface roughness of the national standard GB3505-83, GB1031-83 after the promulgation of the surface finish has been no longer used, the surface finish and surface roughness with the corresponding control table. Roughness has a measurement formula, while the finish can only use the sample gauge control. Therefore, roughness is more scientific and rigorous than the degree of finish.

Surface roughness refers to the processing of the surface has a small pitch and tiny peaks and valleys of unevenness. The distance between the two peaks or two valleys (wave spacing) is very small (below 1mm) it belongs to the micro-geometric shape error. The smaller the surface roughness, the smoother the surface, the surface roughness is generally formed by the processing methods used and other factors, such as the friction between the tool and the surface of the part in the machining process, the plastic deformation of the surface layer of the metal when the chips are separated, as well as high-frequency vibration in the process system. Due to the different machining methods and workpiece materials, the depth, density, shape and texture of the traces left on the machined surface are different.

Surface roughness and mechanical parts with the nature of the fit, wear resistance, fatigue strength, contact stiffness, vibration and noise, etc., has a close relationship with the service life of mechanical products and reliability has an important impact on wear resistance, the rougher the surface, with the effective contact area between the surface of the smaller, the greater the pressure, the greater the more force, the faster the wear and tear, affecting the stability of the fit between the fit, the more rough the surface of the surface of the more easy to wear and tear, so that the gap gradually increased in the working process. Gap gradually increase in the working process; for the interference fit, due to the assembly of the microscopic peaks flattened, reducing the actual effective interference, reducing the strength of the connection.