Calculation of Surface Roughness Parameters of Parts in Designing Accuracy Standards for Critical Joints

The dependences for calculating corrections for surface roughness crimpling of parts are proposed. The presented dependences allow one not only to determine the crimpling rate of the surface roughness at the time of joint formation, but also to limit the roughness rate to form the required contact area. Considering that Ra is standardized for critical surfaces of parts and Rz must be used to calculate the crimpling rate, the dependences for converting Ra to Rz are clarified. A comparative table is compiled confirming the correctness of the calculations in the range of Ra = 0.1–2.5 μm. Using the example of calculating and selecting a force fit, it is shown that different fits are obtained: ∅30H8/y8 with permissible values of surface roughness of the hole and shaft, and when using those specified in the drawing, ∅30H9/z9.