True shape and Apparent shape of Section

TRUE SHAPE AND APPARENT SHAPE OF SECTION

If a solid is sectioned by a plane and it is projected to a plane parallel to it, the shape of the section obtained will be exactly the section exposed by the cutting plane. This shape is called the true shape of section.

If the cutting plane is inclined to the plane of projection, the shape obtained will not be the true shape. Such a shape is called the apparent shape of section.

Fig. 15.10(i) shows a cylinder in simple position, axis being perpendicular to HP and parallel to VP. Let the cylinder is cut by an inclined plane, inclined to HP and perpendicular to VP (called as auxiliary inclined plane, cutting plane is shown by its vertical trace on front view and the top view is in section as shown in figure). The section shown in topview (ie., hatched suface) is inclined to the cutting plane, hence known as "Apparent shape of section" or simply known as "Apparent section". To get the true shape of section, simply known as "True section", the sectioned surface is projected to a plane parallel to it as shown in Figure 15.10(i).

Similarly if the cylinder is cut by an inclined plane, inclined to VP and perpendicular to HP (called as auxiliary vertical plane, cutting plane is shown by its horizontal trace on top view and the front view is in section as shown in figure), the section shown in front view is inclined to the cutting plane is the "Apparent section" and the sectioned surface projected to a parallel plane is known as "True section", shown in Fig. 15.10(ii).