A Worked Example

Following the precedent set by the previous examples, DSG will now be demon-strated. This time the piece that caps the top of the handle will be built. This top piece is chosen because it is simpler and, in comparison with the base, easier to describe with DSG.

The object will be created with an "artsy-geometric" look rather than splined surfaces (Bartels et al., 1987; Riesenfeld, 1993;Puttre, 1992). Of the eight DSG prim-itives mentioned, the shapes that will be removed are mostly in the category of cham-fers.In addition, onepocket will be created.

The first step is to establish and create the bounding block from which mate-rial will be removed by DSG (and later by machining). The SolidWorks CAD package will now be used rather than AutoCAD. As emphasized previously, this is

110 ProductDesign, Computer Aided Design (CAD), and Solid Modeling Chap. 3

merely to show some variation in this chapter. and any of the commercial CAD envi-ronments could have been selected for this tutorial.

The bounding block (or stock) is created by sketching its outline on one of the three coordinate planes and then extruding this outline through space to create a solid object. In SolidWorks, each of the three coordinate planes can be selected in the left window. When one of the coordinate planes is selected, it is highlighted in the right window and looks much like a playing card floating in space.

After selecting the desired coordinate plane, the sketch icon on the vertical toolbar on the right is clicked. This puts the user in sketch mode. A sketching toolbar on the right now becomes visible. A rectangle is sketched using the rec-tangle icon on this sketching toolhar. Dimensions and constraints are added so that the position and dimensions of the rectangle are fully defined. Note that in Solid-Works, the lines on the sketch turn black when they are fully constrained (meaning that there is no ambiguity as to their position and size). Once the sketch is fully defined, the extrude boss/base icon at the top of the left toolbar is clicked. The user specifies the distance that the sketched contour (a rectangle in this case) will be extruded out of the sketching plane. The contour is then extruded into a solid part, as shown in Figure 3.27.

Now that the bounding block has been created, material must be removed using DSG operations to create the final part. Most of the features to be removed in

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3.11 Third Tutorial: Solid Modeling Using Destructive Solid Geometry (DSGJ 111

the design of this part are chamfer features. In SolidWorks, chamfers can be created in two ways, contrasted in Figures 3.28 and 3.29 and described below:

• The first and most obvious (and the one that would usually be used) is to select the edge on the part that will be cut away and then click the chamfer icon on the left toolbar. The user is asked to specify two parameters to define the chamfer. For the one shown in Bgnre 3.28, the angle of the chamfer and the distance that it cuts into the top face were specified .

• Second, the same feature could be cut away using the extrude cut operation as well. In order to create the chamfer in this way, the side face of the bounding block is selected. The sketch icon on the right toolbar is then clicked. This allows the user to sketch on the face of the part.A triangle is sketched as shown in Figure 3.29. The triangle is then selected, and the extrude cut icon (second down on the left toolbar) is clicked. The user specifies "through ell" as the cut depth, and the chamfer is created. Note that this is a more difficult way to create the chamfer and would not be used in most situations.

The chamfer operation is then repeated seven times to create the eight cham-fers shown in Figure 3.30. This is an exploded view showing the geometry removed by each of the chamfers. The numbers shown represent the order in which the chamfer operations were performed.

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112 Product Design, Computer Aided Design (CAD), and Solid Modeling Chap.3

Fipre 3.3G Exploded view of all chamfers.

The next, and final. DSG feature to remove is the recess for the top button. This recess is a pocket, in the language ofDSG-related CAD/CAM. Unlike CSG, a pocket cannot be constructed by removing a prism of any height greater than a minimal height from the substrate. The depth of the DSG pocket has to be exact.

To create the pocket in SolidWorks, the contour of the pocket is sketched on the face into which the pocket will be cut. As explained earlier, to sketch on a face, the face is selected and then the sketch icon on the right toolbar is clicked. The sketch tools on the right toolbar are used to draw the desired contour. Once again, dimen-sions have to be added to fully define the position and size of the sketched contour.

Once the contour is finished, the extrude cut icon on the left toolbar can be clicked.

The desired depth of the pocket is then specified. The completed part with the pocket is shown in Figure 3.31. Note that the fillets on the comers can be added to the sketch before or after the cut operation. In either case, it is accomplished by selecting the comer to fillet and then clicking thefilleticon on the left toolbar. As in the base example, some details are still to be added, including the method of attachment by screws.