Surface finish

Surface finish is a term for roughness in surface inspection. Roughness can be completely eliminated by various processes such as polishing or lapping, but this can be time-consuming and expensive. In addition, a perfectly smooth surface is neither necessary nor desirable in most cases; rather, components require a precisely defined roughness depth. The roughness depth of surfaces is usually specified in μm as the center roughness value Ra (average of the deviations from the center line) or as the average roughness depth Rz (the average of the measured roughness depths). Before the invention of modern measuring instruments for determining surface roughness, it was referred to by the terms rough (scores can be felt and are visible to the eye), smoothed (scores still visible to the eye) or fine smoothed (scores no longer visible to the eye). Today, modern stylus instruments and non-contact measuring methods based on confocal technology make it possible to determine and analyze surface quality in far greater detail. In technical drawings, roughness is entered alongside other surface qualities as a parameter in the surface specifications with special symbols standardized in accordance with DIN EN ISO 1302.