OVERVIEW

Profile, in the aspects considered in the following discussion, is that part of the contour of a technical part or feature that is observed as its boundary line in a functionally significant cross-sectional plane. Such planes for regular geometric figures are the axial plane of a body of revolution, or the central plane of other types of symmetrical parts. From a functional point of view the profile may be considered in a plane perpendicular to the operational displacement movement, such as the cross-sectional plane of a guideway normal to the direction of translation of the guided member. Or, it could be the tangential plane in relation to a rotational path, as in a selected section of a propeller blade.

The basic profiles of engineering parts can have regular geometric forms, such as straight lines or circles (to be discussed in Chapter 14 under "Circular Contour Measurements"); a combination of straight lines and circular arcs in specific angular relationship to each other, such as thread forms; generated forms, such as the involute used in gears; or irregular forms developed to accommodate particular operational conditions (such as the camber or crown of a member subjected to heavy loads). Finally, the functional role of a part may require a form that varies over the surface, and although the changes are gradual and blend into each other, for practical reasons such shapes are often specified and measured by the profiles of precisely defined gaging planes, typical parts in this category being turbine blades...