Chapter 7. Auxiliary Views
Auxiliary views are orthographic views used to present true-shaped views of slanted and oblique surfaces. Slanted and oblique surfaces appear foreshortened or as edge views in normal orthographic views. Holes in the surfaces are elliptical, and other features are also distorted.
Figure 7-1 shows an object with a slanted surface that includes a hole drilled perpendicular to that surface. Note how the slanted surface is foreshortened in both the normal top and side views, and note that the hole appears as an ellipse in both of these views. The hole appears as an edge view with hidden lines in the front view, so none of the normal views show the hole as a circle.
Figure 7-2 shows the same ...