Unit 5 Multiview Drawings 79
A second type of flat surface is the inclined
surface. An inclined surface is perpendicular to
one plane of projection, but inclined to the other
two planes of projection. If inclined surfaces are
examined with respect to the three principles:
An inclined surface appears as a line in only
one of the three regular views.
An inclined surface appears as a foreshortened
shape in two of the three regular views.
Study Figure 5-8B. Surface C is perpendicular
to the frontal plane, so it appears as a line in the
front view. However, it is inclined to the horizontal
and profile planes, so it appears as a foreshortened
shape in those two views. Analyze surfaces A
and B in the same way. In summary, the shape of
an inclined surface appears twice in three regular
views, but a normal surface shape only appears
once! The normal surface is true size and shape, but
the inclined surface is never true size and shape in
a regular view.
A third type of planar surface is the oblique
surface. An oblique surface is not only inclined, but
rotated. Therefore, it is inclined to all three planes
of projection. It is not true shape and size in any
view. In fact, it may appear a little distorted due
to the projection angle it forms with the projection
plane. It also does not appear as a line in any view.
See Figure 5-9.
Cylindrical and Curved Surfaces
Cylindrical surfaces present another set of visual
challenges to the print reader. Technically, cylindrical
surfaces are made of thousands of “elements” that
form a curved surface about an axis, Figure 5-10. The
designer has often planned it so that a flat surface is
tangent to a curved surface, thus making a smooth
transition between the curve and the flat. See objects B
and D in Figure 5-10. In these cases, no lines are
shown at the element of tangency. Be aware, however,
some CAD programs that automatically generate
the views from the model show these elements of
tangency. Also, when flat surfaces form intersections
and cutouts with cylindrical surfaces, the projections
can be tricky. Study Figure 5-11 to help you visualize
how cylindrical surfaces are projected in multiview
drawings.
‚
‚
B
B B
B
X
X
X
X
Figure 5-9.
An oblique surface is not only inclined, but rotated.
Surfaces B and X are oblique surfaces.
No visible
line here
No visible lines
at tangencies
A
B
C
D
Figure 5-10.
Cylindrical surfaces. A flat surface is often tangent to a
curved surface, as shown in B and D.