Elements of positioning and workholding

Abstract

In order to produce a mechanical part correctly, it must be on a suitable set-up (or jig) which guarantees a well-defined location (position and orientation) in space. The surfaces of the jig represent data references for the coordinate system in which the different features of the part are defined. As an example, Fig. 7.1 shows a prismatic part located on three orthogonal planes simulating datum surfaces existing in the physical jig. These planes are used to set the manufacturing dimensions of the features in the part. As mentioned already in Chapter 2, the exact definition of datum features is found in a recent standard (ISO Standard 5459, 1981) distinguishing between simulated and real datum surfaces.