80 Print Reading for Industry
Fillets, Rounds, and Runouts
Molded and cast objects have rounded edges
called fillets and rounds. See Figure 5-12. Fillets are
interior rounded edges. Rounds are exterior rounded
edges. Most CAD programs have a command called
FILLET
to perform this task of rounding corners,
both interior and exterior.
These rounded corners also create situations
where the drafter has to decide whether or not to
project the edge. Conventional practice calls for the
lines to be shown if needed for clarity in describing
the object. This is sometimes a judgment call. If the
edge is shown, the line is projected as if the corner is
sharp or square. When a rounded corner intersects
a curved surface, the edge fades, or “tails” out. This
is called a runout. Note, however, this is different
than runout as defined in Unit 13, Geometric
Dimensioning and Tolerancing. See Figure 5-13 for
an example of how runouts may be drawn. This is
another case wherein views automatically created
from a 3D model by the CAD program may differ
from views created by a CAD operator using two-
dimensional CAD lines and conventional practice.
Meanings of a Multiview Line
In summary, there are many different
perimeter shapes that a flat surface can have,
from circular, to square, to polygonal. Yet, if the
surface is perpendicular to the projection plane, it
simply projects as a line. Therefore, many lines in
a multiview drawing represent the edge view of
planar surfaces. Curved surfaces also are seen as
edge views if the curved surface is perpendicular
to the projection plane. See Figure 5-14.
A second meaning a multiview line can have
is simply an intersection—an edge where two
surfaces meet and nothing more. A third meaning
a multiview line can have is the maximum contour
element of a curved surface. In some views, this
will be represented by a line. These are the three
Figure 5-11.
This figure helps illustrate how cylindrical surfaces are projected in multiview drawings.
Fillet
Round
Figure 5-12.
Molded and cast objects have rounded edges called
fillets and rounds.