"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