OVERVIEW

Considering surfaces as the boundary areas of solids, such as technical parts, the characteristics of a surface can affect various conditions that contribute to determining a part's functional properties. It is the surface of the part that is in contact with the adjacent surfaces of other parts to which it is operationally related. The form and the size of the part are perceived and measured by sensing its bounding surface.

Most technical parts are conceived as regular geometric bodies, or as the combination of such three-dimensional figures. Theoretically, these figures are bounded by surfaces of defined forms, the cross-sectional contours of which are commonly straight or circular lines. However, it is well known that such a theoretical concept cannot be accomplished in manufactured parts, although it is being approached to various degrees. The extent of permissible variations from the ideal is commonly specified on the product drawings as tolerances of size, of form and of surface texture. The inspection and measurement of size and form have been considered in the preceding chapters; the concept of surface texture and its metrology are the subjects of the following discussions and evaluations.

As an analogy, we might compare a technical part with our planet. Thus, the surface of the latter may be considered at three different levels of observations. The basic form is associated with the geometric concept of a sphere or, more precisely, of an oblate spheroid, having specific dimensions and form. The major variations of the earth's surface from a...