Figure 6.16 shows plans and elevations, and defines tool angles, of a plane rake face turning tool oriented in a lathe. The treatment here is in terms of that, but (as has just been written) the results may be applied to any other machining process. O*A is paral-lel to the depth of cut direction and O*B to the feed direction of the machine tool (the cutting velocity direction O*C is normal to both O*A and O*B). The cutting tool has major (or side) and minor (or end) cutting edges which, in projection onto the O*AB plane, are inclined at the approach angles y and k′r to O*A and O*B, as shown (y here is p/2 minus the major cutting edge angle kr introduced in Chapter 2). In addition, the tool has a nose radius rn, also measured in the O*AB plane. The slope of the rake face is determined by the angles, af (side rake), that the intersection of the rake face with the plane through O* normal to O*A makes with O*B and, ap (back rake), that the inter-section of the rake face with the plane through O* normal to O*B makes with O*A. Clearance angles gf and gp and the sign conventions for the angles, + or – as indicated, are also defined.