Unit 5 Multiview Drawings 77
principal planes of projection will be established and
only three regular views used. The front view will
project onto a plane called the frontal plane, the top
view will project onto a plane called the horizontal
plane, and the right side view will project onto a
plane called the profile plane. See Figure 5-5.
With these three planes of projection in mind,
here are some principles to help you read the print.
Principle One. A flat surface is oriented
perpendicular, parallel, or inclined to a plane
of projection. See Figure 5-6.
Principle Two. As a result of Principle One, all
flat surfaces appear in a multiview drawing as:
A) a line, if oriented perpendicular.
B) true size and shape, if oriented parallel.
C) foreshortened, if oriented inclined. See
Figure 5-7.
Principle Three. All surfaces appear in every
view of a multiview drawing, even if only as
a line and even if represented by a hidden line.
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Three Types of Surfaces
There are three basic types of flat surfaces in an
orthographic projection. A normal surface is parallel
to one of the three projection planes and, therefore,
perpendicular to the other two. For example, each
surface of a cube is normal and the top flat surface
of a cylinder is normal. If normal surfaces are
examined with respect to the three principles:
A normal surface appears true size and shape
in only one view.
The normal surface appears as a line in two
of the three regular views.
Think about this for a while. Very often, when
you look at a line in a multiview drawing, you are
looking at the edge view of a surface. When you
look at the front view of a cube, you see the top and
right side surfaces as lines. Study Figure 5-8A. With
respect to the top surface of the cube in the front
view, if you only “see” the front edge along the front
surface, you are still thinking in two dimensions.
As your visualization ability increases, you will see
these lines as surfaces that extend back.
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Frontal
Pr
o
fil
e
Horizontal
Fr
o
n
ta
l
H
F
F P
H
P
Figure 5-5.
Three basic projection planes are used to explain multiview drawings.