TABLE OF CONTENTS Mass finishing typically smoothes external surfaces and cleans them at the same time it removes burrs. Because they combine part improvement attributes mass finishing processes are exceptionally useful. But the term "surface finish" is often used to express several different attributes that affect the end result. Too often individuals debate the surface finish requirement while what they are really looking for is uniformity and lack of surface damage.
Surface finish is generally considered to be the quality of part surface smoothness. In practice, finish is typically referred to as "surface texture" and has four attributes:
Roughness uniform fine irregularities in texture produced by the manufacturing processes.
Waviness an undulating topology of much coarser frequency than roughness.
Lay the direction at which irregularities occur.
Flaws irregularities that have no uniform pattern (includes cracks, pits, checks, ridges, scratches, etc.).
Figure 3-1 is a two-dimensional picture of waviness and roughness. The form shown can be of either attribute, depending on the scale used to make the measurements. As shown here, rough-ness and waviness are both deviations from the desired nominal dimension. Figure 3-2 provides a composite illustration of all the attributes of surface texture that have been described. Figure 3-3 gives a view illustrating the relationship between average roughness and main dimensions.
Mass finishing changes a part's average roughness, but does not generally affect lay or waviness. Mass finishing can remove shallow flaws, but, as will be noted later, in Chapter 4, it can also cause a...
