By John Wilson
Mechanical Desktop (MD) is Autodesk's most versatile CAD product to date. For starters, MD is built on Autodesk's AutoCAD and uses its interface and command structure, so it can do anything AutoCAD can do. Second, MD is a capable surface modeler that can perform such sophisticated operations as two-rail sweeps with intermediate profiles. Third, it's a robust, feature-based parametric solid modeler.
Since MD first appeared almost five years ago, Autodesk has issued a new release every 10 to 14 months. The program is now entering maturity, and evidence of this is in Release 5's relatively modest additions to its set of geometry-creation tools, and in the absence of dramatic changes in its interface. Nevertheless, I think most users will appreciate this release.
Overall, usability has been improved. For instance, as you're selecting parameters for an operation (such as an extrusion) within a dialog box, you can zoom, pan, and rotate viewpoints transparently. Also, the options for specifying sketched feature terminations have increased. You can assign different colors to individual features within a part, and chamfer all the edges of a selected face with one pick. It's worth noting that AutoCAD 2000i is now the platform, rather than AutoCAD 2000. The differences between the two are subtle, however, with Auto CAD 2000i being more closely tied to the Internet. Another addition to the program is the ability to bend existing 3D features.
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| Some geometric shapes that are beyond the ability of solid modeling can easily be made as a surface. Mechanical Desktop can now convert surface objects, such as the one shown on the left in this figure, into solid objects, as shown on the right. |
Among the new sketch-related features are open profile sketches. Open profiles are useful for making thin-walled objects, primarily because you can draw their profiles as a string of lines and arcs, and specify a wall thickness when you create the 3D feature. In MD 5, a sketched feature-type named Rib is introduced. Rib features are similar to extrusion features in that they form a 3D object by pushing a profile linearly. They differ from extrusions in that they must be made from an open profile, and they push the profile along the drawing plane rather than perpendicular to it. As their name implies, they are especially useful in creating strengthening ribs.
In the new release, arrays (operations that make multiple copies of an object) are now called patterns, and they involve more than a change in terminology. Rectangular patterns, for instance, are much more flexible than the old rectangular arrays-columns no longer have to be perpendicular to rows, and you can establish the pattern distribution plane on the fly. Polar patterns are basically the same as polar arrays. A new arrangement, called an axial pattern, is similar to a polar pattern, but in addition to rotating the feature copies around an axis, the copies are distributed along the axis to form a spiral-like pattern.
New surfacing capabilities include surface-to-solid conversion, and some new tools. Even though the gap in geometry-creation abilities between parametric solid modeling and surface modeling has narrowed in the past few years, some shapes cannot be made as solids but can easily be made as surfaces. Now you can convert an MD surface object into a solid object by specifying a thickness and an offset direction. Among new surfacing tools are one that fills open space between two surfaces with a blended, controlled continuity surface, and others that improve quilting and stitching.
A simple press release announced MD 5's availability, and before that there were virtually no clues that it was upcoming. However, Autodesk's Web site states that the company does not plan to discontinue MD, and will continue to enhance it for several releases past 5. So if you currently use MD, you'll definitely want to take a close look at this latest release.
John Wilson runs a design and drafting company. He is the author of 3D Modeling in AutoCAD.Price: $5100; upgrade pricing available
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