Questions about surface roughness
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I wonder if people often see values such as 1.6, 3.2, 6.4 etc. indicating the surface roughness of parts in mechanical drawing. Can the surfaces of parts with these values be distinguished with the naked eye? Are there any existing patterns for comparison, so that it’s easy to tell which one has a higher roughness and which one has a lower roughness?
I found some pictures of surface roughness samples online; they’re more or less like these.
It can be observed with the naked eye across two levels; generally, touching it with the hand is a more direct way. There are also specialized roughness instruments that can measure with precision
It can be observed with the naked eye across two levels; generally, touching it with the hand is a more direct way. There are also specialized roughness instruments that can measure with precision
My previous factory had steel plates with roughness references, but now instruments are used instead
The painting departments are all equipped with surface roughness meters
Repost: Surface roughness refers to the small spacing and minor unevenness in peaks and valleys present on a machined surface. The distance between its two peaks or two troughs (the wavelength) is very small (under 1 mm), making it difficult to distinguish with the naked eye; therefore, it constitutes a micro geometric shape error. Surface roughness has a significant impact on the performance of parts. Generally speaking, a lower value for surface roughness improves the quality of the fit, reduces wear, and extends the service life of the parts, but it increases the processing costs of those parts. Therefore, it is necessary to select the surface roughness value correctly and appropriately. When designing parts, the choice of surface roughness value is determined by the role of the part in the machine. The general principle is to choose a larger value for surface roughness, provided that the technical requirements are still met. When making a specific choice, the following principles can be referred to: (1) The roughness value of the working surface is lower than that of the non-working surface. (2) The roughness value of the friction surface is lower than that of the non-friction surface. The higher the friction speed of the friction surface, and the greater the unit pressure it experiences, the higher it should be ； Rolling friction surfaces require a lower roughness value than sliding friction surfaces. (3) For clearance fits, the smaller the fit clearance, the lower the roughness value should be ； For interference fits, in order to ensure a strong and reliable connection, the greater the load, the lower the required roughness value. Generally, the roughness value is lower for clearance fits compared to interference fits. (4) The surface roughness of the mating surface should be commensurate with its dimensional accuracy requirements. When the matching properties are the same, the smaller the part size, the lower the roughness value should be ； For the same precision grade, smaller dimensions have lower roughness values than larger ones, and shafts have lower roughness values than holes (especially for precision levels IT8 to IT5). (5) The roughness values of surfaces subjected to cyclic loads, as well as internal corners and recesses where stress concentration may occur, should be low.