Chapter 9 Multiview Drawings 205
Visualizing the Object and
Projecting Views
Before a drafter can generate the necessary
views for a multiview drawing, he or she must
be able to visualize the object being drawn. In
other words, the drafter must be able to see the
object in three dimensions in his or her mind’s
eye. This is an essential skill in drafting. There
are many methods and techniques that aid in
the process of visualizingobjects. The following
approach should help the beginning drafter
become successful at visualizing objects.
To obtain the two-dimensional views
needed for a multiview drawing, the drafter
should fi rst think of the object as being enclosed
in a hinged glass box. See Figure 9-3. The
six surfaces of the glass box are the standard
projection planes to which the individual views
are projected. The process used in projecting
the views to the projection planes is known as
orthographic projection. This process allows
three-dimensional objects (objects having
width, height, and depth) to be shown on a flat fl
surface having only two dimensions. The flat fl
surface may be a piece of paper or the screen
of a computer monitor. Orthographic projec-
tion is the key tool used in developing views
for engineering working drawings (drawings
used to manufacture or construct objects).
There are two ways to project views in
orthographic projection, Figure 9-4. Third-
angle projection is preferred in the United
States. First-angle projection is typically used
in most European countries.
The difference between the two types
of projection relates to the placement of the
imaginary box in one of the quadrants formed
by the intersection of the three principal
planes. Referring to Figure 9-4, these planes
are the frontal plane, horizontal plane, and
profi plane. The file frontal plane represents the
projection for the front view of an object. The
horizontal plane represents the projection for
the top view of the object. The profi plane file
represents the projection for the side view
of the object. In third-angle projection, the
imaginary box containing the object rests in
the third quadrant (the lower-right or third-
angle quadrant when looking at the profilefi
plane). In this type of projection, the sides of
the object are projected to the sides of the box
and toward the viewer. In first-angle projec- fi
tion, the imaginary box containing the object
rests in the fi rst quadrant (the upper-left or
fi rst-angle quadrant when looking at the fi
profi plane). In this type of projection, the file
sides of the object are projected to the sides of
the box and away from the viewer.
A graphic explanation of third-angle pro-
jection is shown in Figure 9-5. In this method,
the object is viewed from points of view that
are perpendicular to the projection planes (the
surfaces of the glass box). The drafter looks
through the given projection plane and the
surfaces, edges, and intersections that make
up the object are then projected forward to
the projection plane. That is, the views are
projected to the six sides of the glass box.
Figure 9-3 Visualizing a three-dimensional object
inside a hinged glass box helps establish the planes
of projection for projecting views.