Optimizing Your Model (MCAD Modeling Column)

Simplify your design process to spend less time with procedures and more time making things right.

The company I work for employs approximately 250,000 people worldwide. It's a fairly big company by any standards. Of course, not everyone works in such a big company. Many people work in a company where the same person is responsible for model design, creation, analysis, sourcing, and drafting. If you are one of those workers, you've got a heavy load, to be sure.

The debate about 2D versus 3D rages every day. For most things, I tend to drop heavily on the 3D side, but I realize that 2D retains a definite place. In a company where you are forced to wear so many hats, how do you manage it all?

My company tries to make streamlining an art form. It's constantly looking for ways to reduce costs. Streamlining what they do and how they do it is a lifesaving occupation for busy people. And it should be required learning in school. The concept is simple: The easier you make it, the less time it will take and the more time you'll have for making things right. Yeah, it's the old K.I.S.S. principle — Keep It Simple, Stupid. Whoever came up with it sure knew a thing or two!

But you make complex 3D products. How can you ever hope to simplify them? Well, you'll notice I haven't really said that you should simplify the products. Instead, you should simplify how they're modeled. There are many ways to do it, too.

Sketching

If your modeling system is set up for sketching, I have a few tips that will definitely improve your workflow.

First, constrain what is important to the design. Don't just throw dimensions and geometric constraints willy-nilly. Be organized about it. Dimension as if you want it to appear on the drawing (more on that later). Doing so will make your job easier. Your sketches won't be as apt to explode on you if you are careful in what you do. Also, if someone else works on your files, they won't have to stumble around in them looking for what you did before they can proceed with what they need to do.

Second, make your sketches as simple as you can, within reason. I know a man who loves to have a short feature tree so he jams everything he can into his sketches (figure 1). He says he feels it gives him more control to have a one-stop-shop, as it were, in his sketch. I understand where he's coming from, but he's constantly calling me over to help him figure out why he can't make the model do something. When I make suggestions, he can't do them because of the way his sketch is dimensioned. If he broke the big sketch down into several smaller sketches, they would be easier to deal with. Divide and conquer!

Figure 1. This sketch is far too complicated. It should be broken up into separate sketches. Doing so will simplify each sketch and make changes easier.

Third, don't put radii in your sketch unless it's important to the model (figure 2). Sometimes radii are appropriate, but mostly they complicate your sketch unnecessarily.

Figure 2. A good rule is to sketch a radius only when it's necessary for a given dimension. Here, the important dimension is the tangent of the arc.

Fourth, sketch what you can. It's much easier to make changes to sketch dimensions than any other way.

Features

The way you model will make — or break — any attempt at savings. A badly modeled part will be difficult to edit. Periodically, it will explode on you. It will corrupt assemblies that use it. In short, a bad model is just that — bad. I once worked with a man (more than one, actually) whose models would consistently bomb on us. We never found out exactly what he was doing to cause this failure, but rest assured that when we were asked to work on one of his files, we knew there would be trouble.

One really good way to streamline modeling and make it more bulletproof is to initiate company-wide modeling standards. This subject is touchy with some people, but doing it helps avoid a lot of extra work. You don't have to go through all the trouble of writing up an ISO document, although it might help enforce your new standard. Simple things such as layer control can make life so much easier. If you always put your models on certain layers and everyone knows them, no one has to guess where to look for things. It's the same with every kind of entity you create.

The hard part of standards, of course, is enforcement. If no one follows them, they aren't much help. You're always going to have an anarchist or two who doesn't want to be told what to do.

Put your blends — rounds, fillets, or whatever you call them — on as features instead of part of a sketch whenever possible (figure 3). Unless they are an important part of how a model is defined, leave them for last. You'll find them easier to apply, and your model's performance will be better without all those extra features.

Figure 3. It seems that each 3D modeler calls them something else, but blends are a vital part of any model. Do your-self a favor and try to put them on last.

My mother would hate to hear me say this, but I realized a long time ago that if you don't have to do something, don't. And what you can put off until the very last, do. It sounds bad but it works great! But be careful. In history-based systems, blends often overlap and become dependent upon one another. If you change one, another might no longer work.

Drafting

The drafting process definitely can be streamlined. One of the best ways is not to do it yourself. Have a trained drafter do your drawings. You'll find you get better, more consistent, industry-standard output that way. After all, they're specially trained for the job; it's what they do. (That's a plug for all my drafter friends out there.) If you can't get a drafter and have to do it yourself, then by all means study up on the basics. A lot of unfortunate cost overruns have been caused by poor drawings (figure 4).

Figure 4. Be careful how you dimension things. If you hold everything to ±.005, you could possibly add extra tolerances. One design (top) has a possible tolerance of ±.010, and another design (bottom) has a possible tolerance of ±.005.

One good way to ensure that you at least start out well is to inherit your sketch dimensions onto your drawing. Many — I would say most — 3D modeling systems allow you to do that. What this does is copy whatever dimensions are in your sketches onto the drawing. You'll usually get multiple copies of dimensions because most systems will put them in any view in which they are likely to make sense. You'll need to make sure you have the dimension in the view you want it in and that it appears only once on the drawing.

Another advantage of inheriting your sketch dimensions is that you can make changes to your model from the drawing. Say, for instance, you need to change the length of your part. If you have an inherited dimension, it's just a matter of editing the dimension and the model will update. I know engineers who abhor the idea of a drafter having that kind of ability, but come on. Who's going to make changes to the model after it's in production? Not the high-paid engineer. Why not make things easier for drafters?

Organizing Your Model

When you discuss optimizing your models, you'll hear the word organize a lot. I have written plenty about organizing your models, so I won't go into it again. Suffice it to say, it's important.

Hand in hand with organization is flexibility. Build as much flexibility into your models as you can, and you will reap many benefits. Sure, it takes some thought up front — where fully defined information is hard to find — but in the long run it's worth it. If you take these things into account before and while you build your models, you'll end up with higher quality models that people won't mind working with.

Mike Hudspeth, IDSA, is an industrial designer, artist, and author based in St. Louis, Missouri.