CAD SYSTEMS

January 2000

Autodesk has entered the last year of the millennium with three new mechanical products.

For the 2D drafters, there is AutoCAD Mechanical 2000, an enhanced version of AutoCAD 2000. AM2K offers nothing beyond vanilla AutoCAD 2000 in the 3D realm, but includes an awesome array of automated 2D drafting routines.

Entering the third dimension (if not the third millennium) we have the fourth major release of Mechanical Desktop, Autodesk's second AutoCAD 2000-based mechanical application, and the focus of this review. Mechanical Desktop, like all its competitors in the middle range of solid modelling software, supports part modelling, assembly modelling and the automatic creation of working drawings from those parts and assemblies.

Finally, there's a whole new program, not based on AutoCAD at all, called Autodesk Inventor. Inventor is a brand new mid-range mechanical modeller that's clearly designed to go head-to-head with the likes of SolidWorks, IronCAD, Solid Edge and, of course, Pro/ENGINEER. We'll be taking a close look at Inventor early in the new year.

	Figure 1. Desktop Browser's Drawing tab tales you straight to a layout (what used to be called Paper Space) where, onca again, you can use regular AutoCAD commands together with MDT4 commands to produce first-class technical drawings.

History of Mechanical Desktop
Mechanical Desktop has one of the more complex histories among Autodesk software products. Although it didn't start as an outside program like CAD Overlay or AEC Architectural, it's the result of rolling a number of formerly freestanding products into a single, up-to-date package.

Prehistory
Long before there was Mechanical Desktop, back in the days of Release 9, in fact, Autodesk developed and-not altogether successfully-marketed a product called AutoSolid. AutoSolid was a freestanding solid modelling program than ran on the Xenix operating system and cost U$5,000 at a time when the full version of AutoCAD cost under U$3,000. A couple of years later, AutoSolid reappeared as the AutoCAD Advanced Modelling Extension (AME), this time running on top of AutoCAD Release 12-and costing a tenth as much as the old AutoSolid.

AutoSolid and the AME used a type of 3D modelling called Constructive Solid Geometry (CSG). The Advanced Modelling Extension didn't last very long either; it was gone with the advent of Release 13, replaced by internal solid modelling code-free to all this time-built on the ACIS kernel.

At the same time, Autodesk was developing its own mechanical add-ons for AutoCAD: AutoSurf, AutoCAD Designer and the IGES Translator. These three programs were evenutally rolled into one: AutoCAD Mechanical Desktop Release 1.

Mechanical Desktop 1-2-3
Mechanical Desktop Release 1 hit the market in mid-1996 and reaffirmed in many users' minds the old maxim about never buying Release 1 of anything-and its prospects were definitely not helped by its being built on AutoCAD Release 13. MDT1 wasn't much more than a packaging of mature (or semi-mature) versions of AutoSurf and AutoCAD Designer, and the perception of Release 1 was that it was weak in both part and assembly modelling.

Release 2 appeared in the fall of 1997. This version, built on the vastly-improved AutoCAD Release 14 and the ACIS 3.0 kernel, addressed shortcomings in assemblies; it was followed less than a year later by MDT Release 3, also built on Release 14 but this time incorporating the then-current ACIS 4.2 kernel. Mechanical Desktop 3 provided many of the missing part-modelling features demanded by its users.

Figure 2. In mechanical desktop, you stay in the drawing file to edit parts and create assemblies. This complex assembly includes localized and externally referenced parts as well as a subassembly.

Mechanical Desktop 4
Now we have the fourth major release of Mechanical Desktop in a little over three years; MDT4 is, of course, built on AutoCAD 2000 and employs the ACIS 5.2 solid modelling kernel. You now have a choice of versions: you can purchase the base model, or you can trick it out with the extra-cost Power Pack option. Power Pack, which is also available for the 2D AutoCAD Mechanical 2000 product, consists of library upon library of parts and symbols (mostly 2D in AM2K, mostly 3D in MDT4) and adds U$1,000 to the price of the program. If you purchase the Power Pack version of MDT4, you get everything in AutoCAD Mechanical 2000 and, according to Autodesk, over one million symbols.

Most work in MDT4 is done with the Desktop Browser on screen. You choose the appropriate tab-model (parts or assemblies), scene (assembly arrangements, such as exploded views) or drawing-and take it from there.

Part Modelling
The basic process of starting a part is to sketch a profile on which to base it. You then resolve or constrain the sketch so it's fully defined; from here you create a feature-the core element of a part-by extruding, cutting, revolving, sweeping or lofting the profile (see figure 1). In previous versions, as in many other solid modellers, you can have only one part in a part file. MDT4 lets you create complex parts in a single file; the original part becomes the part definition, and additional parts-known as "unconsumed toolbodies”-can be added to the part definition.

Assembly Modelling
Unlike some of its competitors, Mechanical Desktop does not use separate file formats for parts, assemblies and models; all three data types use the AutoCAD DWG format. (Of course, you'll need MDT or AutoCAD Mechanical to view the models.)

MDT assemblies can consist of parts created locally or brought in as external references (see figure 2). Similarly, sub-assemblies of parts can exist locally or be externally referenced into a complex assembly. Using xrefs, of course, will let you use the same part in multiple assembly files, but you can localize them-in effect, bind the externally referenced parts-to the current model file.

A handy new feature in Mechanical Desktop 4 is enabled by AutoCAD 2000's in-place reference editing and referred to by Autodesk as "Assembly-Centric” design. In plain English, this is the ability to edit a part from within an assembly and have the changes written back to the original part file. One feature I miss in MDT4 is the ability, in a complex model, to select a part from the drawing and see it highlight in the Desktop Browser, or select something in the Browser and see the part highlight on screen-this would make it much easier to identify objects in both assembly and part files.

Mechanical Drawings
Like all good mid-range modellers, Mechanical Desktop relieves you of most of the work of working drawing creation. Automated procedures set up borders and title blocks-using AutoCAD 2000 layouts, of course-and establish viewports into your model. You can create auxilliary views and sections as well as regular orthographic projections, and you can change your model from a drawing view. Dimensions are added automatically, but you can suppress and add dimensions as required (see figure 3).

Should you Upgrade?
There is absolutely no reason not to upgrade an existing Mechanical Desktop Release 3 or earlier installation to the AutoCAD 2000-based Mechanical Desktop 4. You get all the AutoCAD 2000 improvements in drawing layouts, multiple documents and 3D navigation, plus-if you can use them-the additional features in the Power Pack add-on. (If you're an industrial designer, you may gain less benefit from Power Pack than you would as a mechanical engineer or equipment designer; check the specs closely before deciding whether or not Power Pack is for you.)

Mechanical Desktop 4 is also a reasonable choice for a new purchase as well; the mid-range, solid-modelling marketplace certainly has room for an AutoCAD-based product. However, Autodesk's new Inventor is worth watching too; if you're confused between the two, just consider whether or not you need AutoCAD compatibility.

	Figure 3. The interface looks like that of Another Leading Brand, but a lot like AtuoCAD too. You use familiar commands like PLINE and CIRCLE to create your sketches and, while you still have to manipulate the USC, AutoCAD 2000 features make it much easier.

System Requirements and Installation
The last Autodesk "Desktop” product we looked at was the AutoCAD 2000-based Architectural Desktop Release 2; Autodesk's minimum requirements for Architectural Desktop were a Pentium 133 with 32 MB of RAM. Mechanical Desktop 4 is in another league altogether. Autodesk's minimum "recommended” system is a Pentium II/300 with considerably higher RAM requirements: 128 MB for part modelling, and 256 MB for assemblies.

Installation strikes me as onerous. The ability in regular AutoCAD 2000 and Architectural Desktop to defer authorization for 30 days and run the software until that time expires, is gone. Now, before you can even install the software, you need to enter your 11-digit serial number, 6-character CD Key and-new to Mechanical Desktop 4 and AutoCAD Mechanical 2000-a 12-character product ID code. Once you've done that, you still have to call Autodesk for an 8-character authorization code or your installation will expire in thirty days.

Apart from that, InstallShield does its usual efficient job of installing and configuring your installation. Disk space requirements are as impressive as RAM requirements; a compact installation will take 350 MB, with typical installations running closer to the 450 MB mark.

Summary
Autodesk provides an excellent documentation package for Mechanical Desktop 4. The program includes four manuals: a 270-page Getting Started guide, a 168-page Installation Guide (which covers Power Pack and non-Power Pack versions of both AutoCAD Mechancial 2000 and Mechanical Desktop 4), a 431-page Command Reference, and a 712-page book of Tutorials. The four manuals are provided in both hard copy and Adobe PDF formats.

In addition, separate online Help files are available that guide you through basic skills and more advanced topics. I liked the presentation of the "Quick Guide to Learning” which is meant to teach you the most fundamental steps in part, assembly and drawing creation. It's a good idea, but unfortunately, it's so full of errors that it's difficult to follow.

I also appreciated the enhanced HTML Help system; in general, I prefer the older Winhlp32 system with its Find tab, and think that the HTML system's Search tab is no substitute. But MDT4 includes the old style Find functionality within the new-style HTML system-really the best of both worlds!

Mechanical Desktop 4 is a first-rate solid modelling program and deserves a close look from anyone in the field whether they're considering switching from a different program or not. There's lots to like in MDT4… although there's a good chance you'll have to upgrade your hardware to make the most of it.

David Byrnes is a freelance writer based on Bowen Island, B.C. and you can reach him at dbyrnes@cadsystems.com.