Cadalyst - October 2008 - (Page 39)

mcadmodeling By Mike Hudspeth, IDSA Assault with a Deadly CAD File A few diversionary tactics could help you survive the experience of sharing 3D models. A re you MENSA material? I’m not. Puzzles irritate me. My wife loves to sit for hours ﬁguring them out. I throw puzzles against the wall and go ﬁnd something more fun to do. I guess I’m not the “if at ﬁrst you don’t succeed, try, try again” type. Actually, I’m the type who uses the computer-game cheat books. I don’t play games for the intellectual stimulation; I play them for fun. It’s interesting then that I chose to go into 3D modeling. How so? Let me ask you, How often have you had to use someone else’s model and you felt as if you were taking a MENSA test? You can’t do this, you can’t do that. The model explodes. Does that sound familiar? Just about anyone who deals with 3D models has problems from time to time. It’s not their fault (usually). It’s just that using models from who-knows-where can be challenging. No one has it in for you. When you get a model from someone, he or she usually doesn’t intend to cause problems. But unless everyone does everything exactly the same way, variation will be commonplace. Until the 3D modeling police make people do things the so-called right way, people are going to do their own thing. It’s human nature. I used to work with a bunch of modelers (who shall remain anonymous) who learned to do their jobs piecemeal. Our company was too cheap to send them to training, so they had to pick the brains of those who were lucky enough to have gone. They ended up learning just enough to get their jobs done. They were totally oblivious to the full capabilities of the 3D modeling software. Consequently, whenever a problem occurred with a model, you could bet your bottom dollar it was one of theirs. One engineer in particular was notorious for having models no one wanted to touch. Every time we imported or opened his files (and I do mean every time), they had problems, (You only have to get the blue screen o’ death once or twice before you figure out someone’s not doing something right.) Unfortunately, our deadlines didn’t allow us to remodel, so we worked with what we had. Figure 1. Many manufacturers of off-the-shelf parts offer 3D models you can incorporate into your CAD assembly. Lost in Translation If you have to translate 3D CAD files from one file format to another, you’re probably no stranger to problematic models. CAD file translators today have come a long way and are fairly bulletproof, but not always perfect. Again, the process is hampered by the human desire to do things our own way. If you take a part to five toolmakers and ask each to design a tool to make the part, you are likely to get five October 2008 cadalyst www.cadalyst.com different solutions. It’s the same with 3D CAD software programmers. Each 3D modeling program is different from the next, which means you probably can’t move a model from one to the other without losing something in the translation. In the old days, this problem was even bigger. Many developers would make it difficult to export models to another format because they feared easy file translation might lead to lost business. (What was Genghis Khan’s old saying? “It’s not enough that I succeed, everyone else must fail.”) So translation issues weren’t just intentional, sometimes they were economical. File-translation problems can pop up if you use purchased parts and you download 3D models to represent those parts in your design (figure 1). The manufacturers that produce standard parts can’t always afford seven different 3D CAD modeling programs to create parts models in every popular format. Even if your company owns several 3D modeling programs, you probably model in only one of them, and chances are you usually require some file translation to incorporate 3D models of off-the-shelf parts. When I was new to CAD work, I drew all my parts to three decimal places. It was accurate and simple, but it also was expensive. Some of those dimensions didn’t need to be so tight. I was summarily corrected, and I learned to adjust for what was important and what wasn’t. Unfortunately, a 3D modeling program can’t learn that sort of lesson. So when the user tells the software to round everything to a certain tolerance, that’s what the software does. When that part is translated into another 3D modeling format and the tolerances aren’t the same, problems can occur. The first 39 http://www.cadalyst.com

Table of Contents Feed for the Digital Edition of Cadalyst - October 2008

Cadalyst - October 2008 Contents Editor’s Window Cad Central SimCity for Real Designs Spring to Life — 3D Publishing Tools Make File Sharing as Easy as Opening a Book Xi MTower 2P64X — Dual Quad-Core Workstation ArchiCAD 12 — BIM Software Dell Precision M6300 — High-End Mobile Workstation Cad Manager Mcad Modeling Aec Insight Cad Cartoon Issue Indexes Hot Tip Harry

Cadalyst - October 2008

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