In short, when the interior of the object is complicated or when
the component parts of a machine are drawn assembled, an
attempt to show hidden portions by the customary dashed
lines in regular or graphic views often results in a confusing
networks, which is difficult to draw and almost impossible to
read clearly.
In case of this kind, to aid in describing the object, one or
more views are drawn to show the object as if a portion has
been cut away to show the interior.
For some simple objects where the orthographic un sectioned
views can be easily read, sectional views are often preferable
because they show clearly and emphasis the solid portions,
the voids, and the shape.
Cross-Sectional Views
A cross-sectional view portrays a cut-away portion of the
object and is another way to show hidden components in a
device.
Imagine a plane that cuts vertically through the center of the
pillow block as shown in figure 6.5 (a) and (b). Then imagine
removing the material from the front of this plane, as shown in
figure 6.5 (b).