Perfect smoothness is impossible, if not undesirable. Roughness is the single biggest determinant of the surface texture. All mechanical processes such as sawing, grinding, or drilling result in a certain amount of roughness. It may arise due to the cutting speed and the depth of the tool used to make a cut, or due to the angle at which a cut is made. In any case, since roughness depends solely on the machining, an improvement in the tool used will directly improve the roughness measure of a surface.
Waviness is a feature of a surface finish that arises due to structural reasons. For example, vibrations on the factory floor can cause evenly-spaced irregularities in the finished product. These are more dispersed than those in roughness. Excess waviness is damaging because it leads to warped surfaces.
Lays denote the patterns that arise due to the dominant direction of the machining process. Depending on how the machining is done, the lay patterns can either be vertical, horizontal or circular . Lay constitutes the final element of surface finish that gives the surface a distinct texture and character.