There is a requirement in equipment manufacturing: the inner surface must be smooth, with a Ra value of 0.7. What does Ra mean?

This post was last edited by li*nji on 2019-1-24 at 13:48. Surface roughness, or the quality of a mechanically processed surface, refers to the microscopic irregularities on the surface of a part after machining; it is also known as roughness. Arithmetic mean deviation Ra of the machined surface profile: the arithmetic average of the absolute values of the profile deviations over the sampling length (lr). In actual measurements, the greater the number of measurement points, the more accurate Ra is. Ra0.7 is generally denoted as Ra0.8; it represents a smooth surface with no visible signs of machining, and the direction of machining can only be discerned with difficulty. Processes such as precision turning, precision grinding, precision reaming, and lapping are used to achieve this level of smoothness. There are roughness reference blocks available for comparison, and Ra0.8 surfaces appear similar to those of machine tool guides.

Ra: Arithmetic mean deviation of the contour, which is the arithmetic average of the absolute values of the contour deviations over the sampling length (lr)