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Step Two: Build the Master Model

Once you have decided which model management scheme to use, you are ready to create your Master Model.

1. Get started. Set up separate primary coordinate systems for enclosures and for internal components so that you can manipulate “skins” (cosmetic surfaces) and “guts” (internal components) independently. Then create primary datum planes for significant geometry. For example, a tabletop product might have primary datum planes representing the table surface, the product bottom, and the product top. Create mirror planes for symmetrical products.

2. Import ID geometry. Import any available ID drawings from other CAD programs, but only as a visual reference or tracing template. If you align your Pro/ENGINEER geometry to imported features, you will compromise the program’s parametric functionality. Fold up the orthographic views of 2D CAD drawings into a 3D box either in Pro/ENGINEER or beforehand using AutoCAD, Vellum, or other CAD platforms. For 3D geometry, export the surfaces directly from 3D design tools such as Alias or Rhino using IGES format.

3. Build curves. To define the basic boundaries and outlines of the primary cosmetic surfaces, build datum curves by sketching on the primary datum planes. Use splines wherever possible since they provide cleaner geometry than arcs or conics. Keep the spline “light” by minimizing the number of control points (Fig. 1).

	Figure 1. The sequence of arcs defining the frame around the scroll-key of the Palm m125 was built using a single spline in order to maintain surface continuity and avoid abrupt transitions where the curve inflects.

Where applicable, take advantage of powerful Pro/ENGINEER 3D tools such as Curve: 2-Projection and Curve: Thru Points to create 3D driving curves. When using a multi-segmented curve (comprising several component curves) to drive a surface, use the Curve, Composite, Approximate command, yielding a curve that doesn’t contain multiple boundaries. This step not only gives you a smooth, continuous surface free of tangent lines, but also simplifies the addition of shells, rounds, and other dependent features. Within the sketch, you also can use the Spline, Approximate Chain command, although this approach is more difficult to manage.

	Figure 2. To maintain tangency of the step detail at the back of the inFocus LP750 digital projector, we projected a curve onto the primary surface to drive tangency of the tear detail.

Begin with parting surfaces if applicable, especially when they are non-planar. We recommend using parting surfaces rather than planes, lines, or curves to build functionality and flexibility into your Master Model. From them you can create lips, reveals, and other interface details. Parting surfaces also make it easier for designers to change from a flat to a complex surface as needed.

Then construct primary surfaces—such as the top, sides, and front—that define the part’s overall shape. The parting surfaces often can be used to drive primary surfaces. Project curves onto the primary surfaces to drive tangency and boundaries of secondary surfaces, including scoops, tears, and bulges (Fig. 2).

Be sure to build draft into surfaces whenever possible. You can do so within sketch mode for Variable Section Sweeps simply by adding an angle dimension to your section. Another method is to begin by sweeping a drafted construction surface along one of your boundaries as just described. Then you can build Boundary Surfaces or Swept Blends tangent to this construction surface, maintaining the prescribed draft.

Be sure to create a temporary Surface: Offset as you build each surface. This ensures that it will offset individually and maximize chances the part will shell down the line.