Chapter 9 Multiview Drawings 209
Then, the “sides” of the glass box are unfolded
toward the drafter. The front is always the
featured view with the other views oriented
in the order obtained by unfolding the sides
of the box. In other words, the right side view
is always to the right of the front view, the top
view is always above the front view, the bot-
tom view is always below the front view, and
so on.
A graphic explanation of fi rst-angle fi
projection is shown in Figure 9-6. In this
method, the views are projected to the six
sides of the box and the sides of the glass
box are then unfolded away from the viewer.
When viewing the object from the front, the
surfaces, edges, and intersections of the object
seen from that point of view are projected to a
plane behind the object. In addition, the object
is drawn as if the object were placed on each side
of the glass box. When viewing the object from
the top, what is seen is projected to a plane
below the object. When viewing the object
from the bottom, what is seen is projected to a
plane above the object.
A very easy way to identify a drawing
that has been generated using fi rst-angle fi
projection is to recognize that the views are in
the opposite orientation of how they would
appear in third-angle projection. That is, the
views of the resulting multiview drawing are
oriented so that the top view appears where
the bottom view should be, the bottom view
appears where the top view should be, and
so on. Compare the orientation of the views
in Figure 9-5 to the orientation of the views
in Figure 9-6. Notice that regardless of the
method of projection, all views are centered
about and originate from the front view.
Different symbols are used in industry to
identify third-angle and fi rst-angle projection
drawings. See Figure 9-7. The appropriate
symbol typically appears next to the title
block on the drawing sheet.
Identifying Object Features
An object feature may be defi ned as a
physical characteristic of an object. It may
be a hole that has been drilled, a notch that
has been cut, or an angular cut. It is impor-
tant for the drafter to be able to identify the
features that exist in an object. This is because
the size and location of each feature must be
known for the object to be manufactured to
the designer’s specifications.fi
Features are physically represented as the
negative mass of an object. Let us say that all
objects begin as a solid mass of material. The
solid block has what can be termed positive
mass. Certain manufacturing operations must
be performed on the solid mass to create
the object’s end product. These operations
may include cutting, drilling, boring, and
milling, among others. The important thing
to remember about these operations is that
they all remove material (positive mass) from
and Air-Conditioning Engineers (www.ashrae.
org) and the Society of Automotive Engineers
(www.sae.org), respectively. Special informa-
tion for high school students about careers
in engineering is available from the Junior
Engineering Technical Society (www.jets.org).
If I decide to pursue a different career,
what other fi elds are related to mechanical
engineering? Mathematics, drafting, archi- ?
tecture, other types of engineering, and many
types of science.
Mechanical Engineer
(continued)