"DESIGN IS TO MAKE ORIGINAL PLANS, SKETCHES, PATTERNS, ETC
4. Detailed
design:
"Design is to make original plans, sketches, patterns, etc." (Web-
ster's Dictionary).
The first step in the design of the shovel is the creation of a wire frame drawing to
be extruded into the initial solid of the model.The most complex view of the part is gen-
erally selected for this wire frame, and in this case, the side view of the shovel is selected
for the wire frame drawing.The final shovel design wire frame is shown in Figure 3.33.
Notice the dimensions on the wire frame in Figures 3.33 and 3.34. Unlike
conventional drafting packages where the dimensions are added to document a
specific line length, parametric
design controls the size of the part with these
dimensions. They are therefore called
constraints
rather than dimensions in para-
metric design. Figure 3.34 shows the side view of the wire frame sketch of the
shovel head after the angle constraint has been modified from 32 degrees to 45
degrees. Notice how this simple change dramatically alters the shape of the shovel.
A standard drafting package would require the shovel head to be redrawn and
then redimensioned to make this change.
The ability
to rapidly
change
such
design
parameters
is one of the key strengths
of parametric
design.
Also notice that in addi-
tion to the standard constraints of length, there are constraints for angular, radial,
perpendicular, tangent, and coincident objects in Figures 3.33 and 3.34.
Figure 3.35 shows the solid object from an isometric front view that is created
when the wire frame shown in Figure 3.33 is
extruded
a distance of 225 millime-
ters (9 inches) and draft angles are added for strength and manutacturabillty.
Figure 3.36 shows the same view after
fillets
have been added to the shovel head.
The next step in the shovel design is to add cutouts to the bottom of the
shovel head, which will become the stiffening ribs when the part is turned into a
shell. Figure 3.37 shows a view perpendicular to the back edge of the shovel head
Flgure3.33 Wire frame model of
snow shovel (Thanks are due to Dan
Odcllforhiscontributions).
flgure3.34
124
Product
Design, Computer
Aided Design (CADJ, and Solid Modeling
Chap. 3
Ftpn3.35
F1gure3.36
.••...
..,.,
with the wire frame for the rib cutouts sketched on it. The wire frame cutouts
extend past the actual part that they are intended to cut to ensure that they cut
through the entire part.
Figure 3.38 shows an isometric view of the bottom of the shovel after the wire
frame sketch has been extruded at an angle as a cutout to form the inverse of the rib
profile. In a similar way, Figure 3.39 shows an isometric view of the top of the shovel
after it has undergone ashell
operation and a filleting operation. The shell operation
takes a solid object and offsets its outer surfaces to generate a part of uniform wall