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ORTHOGRAPHIC PROJECTION | Up
Engineering Aid 3 - Beginning Structural engineering guide book | Next
A third-angle projection brought into a single plane |
Figure 5-5.-Elample of a first-angle projection.
Figure 5-6.-Firsl-angle projection brought into a single
plane.
shown in figure 5-5. The cube is supposed to be
fronting toward the vertical plane of projection.
As you can see, you get a front view on the
vertical plane, a left side view on the profile plane,
and a top view on the horizontal plane.
Now, to put these views on a sheet of drafting
paper, you must get them all into the same plane.
You presume that the vertical plane of projection
is already in the plane of the paper. To get the
other two views into the same plane, you rotate
the profile plane counterclockwise and the
horizontal plane clockwise. The projection now
appears as shown in figure 5-6.
This first-angle projection arrangement
of views is considered satisfactory in most
European drafting practice. In the United
States, it is considered illogical because the
top view is below the front view; because
the right side of the object, as shown in
the front view, is toward the left side view
of the object; and because the bottom of
the object,
as shown in the front view,
is toward the top view of the object. For
these and other reasons, first-angle projection is
not used much in the United States.
THIRD-ANGLE PROJECTION.— Figure
5-7 shows a third-angle projection of a cube. As
you can see, you get a front view on the vertical
plane, a top view on the horizontal plane, and a
right side view on the profile plane.
Figure 5-7.-Example of a third-angle projection.
5-4
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