Units: mm (SI), mils (Imperial) The 'normal' range of RMS (root mean square) surface roughness which lies within the capacity of the process. As with mass, an 'extreme' range is also stored. Surface roughness is determined by the nature of the process: the smoothness of mold surfaces in casting and molding or the depth of cut in machining. It can usually be refined by machining, grinding and polishing.
Roughness or rugosity is a measurement (see surface metrology) of the small-scale variations in the height of a physical surface. This is in contrast to large-scale variations, which may be either part of the geometry of the surface or unwanted 'waviness'. Roughness is sometimes an undesirable property, as it may cause friction, wear, drag and fatigue, but it is sometimes beneficial, as it allows surfaces to trap lubricants and prevents them from welding together.