Surface roughness is an important technical index to reflect the microscopic geometric shape error of the part surface, and it is the main basis to test the surface quality of the parts. Whether it is reasonable or not is directly related to the quality, service life and production cost of the product. There are 3 kinds of selection methods for 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, rapid and effective. The application of analogy requires adequate reference materials, and more comprehensive information and literature are provided in the various mechanical design manuals available.
The most commonly used is surface roughness appropriate to 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 function relationship between them. For example, some machines, instruments on the handle, handwheel and sanitary equipment, food machinery on the modified surface of certain mechanical parts, their surface requirements are very smooth, that is, the surface roughness requirements are very high, but its dimensional tolerance requirements are very low. In general, there is a corresponding relationship between the tolerance level and the surface roughness value of the parts with dimensional tolerance requirements.