Surface roughness is an important technical indicator that reflects the microscopic geometric shape error of the surface of the part. It is the main basis for testing the surface quality of the part; whether it is selected reasonably or not is directly related to the quality, service life and production cost of the product. There are three methods for selecting the surface roughness of mechanical parts, namely calculation method, test method and analogy method. In the design of mechanical parts, the most common application is the analogy method, which is simple, fast and effective. The application of analogy requires sufficient reference materials. Various existing mechanical design manuals provide more comprehensive materials and documents. The most commonly used is the surface roughness that is compatible with the tolerance level. Under normal circumstances, the smaller the dimensional tolerance requirements of mechanical parts, the smaller the surface roughness value of mechanical parts, but there is no fixed functional relationship between them. For example, the handles on some machines, instruments, handwheels, and sanitary equipment, food machinery on the modified surface of some mechanical parts, their surface requirements are very smooth, that is, the surface roughness requirements are very high, but their dimensional tolerance requirements are very high. low. In general, there is a certain correspondence between the tolerance level and the surface roughness value of the parts with dimensional tolerance requirements.
