Approaching a Complex Model: Part1 – Shape

Motorcycle featured in Infinite Skills SolidWorks 2012 basic course

This is going to turn out to be one of those multi-part posts. It started as a user group presentation for Daniel Herzberg’s user group in Fredricksburg, Virginia on January 18, 2012, on how to approach complex design in general. Now I get to revisit this and add some detail by turning the powerpoint outline into a series of full-blown blog posts.

I have mostly stopped participating in user groups, but will from time to time go visit a group if the timing is convenient. I definitely burned out on them because I was starting new groups, leading groups, giving guest presentations, and participating with the official SW user group organization, in addition to a full time job. At some point it just became too much, and the motivation seemed to evaporate. While I love hanging out with real CAD users, as usual, it was the behind the scenes politics that brought an end to my enjoyment of it.

I’m going to start converting some of these dozens of old user group presentations that I’ve written into blog posts. The presentations were usually just outlines with a few visuals, with most of the details being filled in with improv. This is probably the main reason you don’t see my presentations on Charles Culp’s site of collected stuff, and why I never submitted actual powerpoint files when I presented at SolidWorks World. The powerpoint was never finished until a few hours before the presentation, and it didn’t have enough information in it to stand on its own. Most of the value of the presentation was in using the SolidWorks software live in front of people, which I think is the way it should be done. Live demo’s show that A) you’re human, and B) the software isn’t as infallible as a rehearsed demo would make you believe.

The models for this series have come from the last 7 years of work or from just stuff I’ve done for writing projects. As with most things here, I’d like readers to contribute their ideas on how they would approach the problem and discuss pros and cons of the various ideas.

What is “complex”? Everybody is going to have a different idea of what this means. To some people, a single part can be complex. And to others it is possible to make something complex out of extruded features. Complexity comes from various sources. It could be the shape, the number of parts, the function, the assembly technique, the external reference scheme, a mechanism, the manufacturing method, number of variations, or other factors.

Batmobile modeled for a series of blog posts in 2010

Complexity is essentially anything you think it is. If it makes you think hard, or your computer chug more than usual, it’s a complex design.


One obvious source of complexity is shape. The complexity of shape can be amplified by extending the shape across multiple parts. Laying out a complex shape is hard enough, but laying out an assembly at the same time makes it trickier.

Very often to layout a complex shape that moves across multiple parts, I might use a combination of real references (sketches or point cloud information that will at some point be used to create the actual shape) and visual references (sketch pictures). Usually, I just deal with something like a model of a car as if it is just a single part. The body may later be broken up into multiple parts, but for the sake of the shape, it has to start as a single part file.

Layout images for the batmobile on all standard planes

After you have your sketch pictures, you create your big shape lines. Work from the direction of least detail (big shapes) to greatest detail. It can be tempting to work from say the front to the back. When you do this, you get the overall shape confused with the detail. You’re better off to just make all of the big surfaces first, which could be done front to back, but then go back and add intermediate detail, then fine detail. As long as we’re talking about complexity, the one thing you can add to any design that adds the most complexity to every design is – detail. This is why demo models have so little detail.

Layout sketches for the batmobile

Some references will need to be 3D references, so projected sketches or 3D splines may be required. Also remember that some reference information will only be created as an intersection of faces that you have to build. This isn’t exactly a linear process, and history modeling is a poor scenario to try to build complex shapes. Remember also about symmetry. Don’t build stuff twice. You should always have a plan for symmetry. Something like “build the right side, mirror only at the end”. But I have to say that a plan like that rarely works out in real life. Sometimes after you’ve made the mirror, you need to make something symmetric, and instead of rolling it back and adding it, you just model it and mirror things again. This is inefficient modeling.

When you look at shapes, one of the things you have to decide is “how 3D is this shape?” A lot of shapes are very 2D. Even some of the shapes on this batmobile were pretty 2D. The main 3D surfaces here were the jet intake and the back end of the car that  isn’t shown. 3D shapes are either easy or difficult. They can be easy because you just draw the beginning shape and the end shape, and let the software take care of what’s in between. They can be difficult if you don’t really have a good idea in your head of how the shape relates to the tools you have at hand.

The most complex shapes are things where you don’t have any real edges to use as reference. If the edges are 2D, you’re in luck, because the rest of it is likely easy. If the edges are 3D, that makes things more difficult. If there are no edges, or you have to extrapolate edges (be mentally removing fillets or blends), that is much more difficult.

Scoop and Fender

The air scoop on the roof of the cockpit area was difficult because it had to blend in, yet it had to stick out. It does have a 3D edge, which was something to go from. The rear fenders were difficult because they had to bulge in a particular way, but still had to cover the wheels. The main difficulty was that there seemed to be 2 driving shapes for the fenders: the flare where it cut for the wheel had to be planar on an overall 3D shape, and yet the face of the fender had to bulge in a masculine and muscular way. The fins were difficult because they were supposed to angle, yet blend into the complexity on the fender. There is no doubt that I took a lot of shortcuts on the batmobile that I would not have been able to take on a part for a real paying project. I usually leave models like this alone, but it might be a good idea to go back and clean up some of the shortcuts in this model. One of the tortures of closet perfectionists is that your work is never ready to show.

In the next blog post on this topic, I’ll take a look at product structure – either as multibody or assembly – as the thing that creates the complexity.

4 Replies to “Approaching a Complex Model: Part1 – Shape”

  1. The more interfaces (surfaces, edges, etc.) you’ve got among parts in an assembly, the greater your complexity. Compound this by simply using some form of compound items (surface, edges, etc.) at those key interfaces. Further compound this by adding vast quantities of parts. It’s at this level I discover all sorts of weaknesses/bugs/flaws in SolidWorks—particularly when designing with master parts that are surfacing-heavy.

  2. @chad
    “I think in-context modeling mixed with configurations…”

    SolidWorks has had problems with this since I started using it in 1999. Therefore, I don’t use in-context modeling mixed with configurations.

  3. I think in-context modeling mixed with configurations is very complex too me. I’ll give you an example. I was making a part with layout sketches in it that had configurations in it to drive an assembly that had these same configurations in it also. The problem I discovered is that driven dimensions are very bad for layout sketches. When I opened the layout part file and changed the configurations everything solved as expected including the driven dimensions. When this same layout part is placed in the assembly the driven dimensions wouldn’t solve every time I changed configurations in the assembly. Why SW is so poor about handling this I’m not sure.

  4. Solidworks often does strange stuff in the mirror plane. A boundary surface may not produce a continuous flat top if the part is modeled in halves. Your batmobile has a hogback in the roof, better than a buttcrack or a tit. 2D splines in sketches may forget about tangent constraints and retain symmetry. If you turn on curvature display and look closely it just about impossible to make a perfect continuous curvature surface. Tiny rolls, waves and tits are lurking at the edges. It matters not that the boundaries are convert entity of a smooth or projected smooth curve. I am working on a wing tip, the minimum radius is 0.125 inch, yet Solidworks adds some nastly little kinks with a minimum radius of 1/10000 inch. The shaded display of surfaces is smoother than the actual surface. Curvature display seems to show the actual shape.

Leave a Reply to Rick McWilliams Cancel reply

%d bloggers like this: