Why Surfacing, Mum?

Surfacing should be avoided like the plague. It’s hard to do. It takes lots of time to learn. It creates complexity and causes stress and confusion.

If you choose Surfacing for a living, inevitably there will be times when you struggle through the night with a complex database in order to deliver a model on time.

If you choose Surfacing, you will find that weeks of intensive, CAD modeling work may need to be re-worked because the products components have been changed or because Marketing requirements have been changed.

So, how about Solids then?

Solids are more straightforward. Generally speaking, solids are many times more robust than surfaces and, moreover, they can be more easily understood by others downstream in the development process. The main reason for the difference is that Solids are WYSIWYG (what you see is what you get) while Surfaces are anything but WYSIWIG.

The construction of a Solid feature is immediate and nearly always clear; a protrusion, a cut, a chamfer, or a round make an impact on your model visibly and measurably. By measurably, I mean that if you were to measure the mass, or the length of a model after each solid feature is added, you will see continual variation in the mass or length at every stage in the models progression.

Compare this with Surfacing. Often, there is only a tenuous or indirect relationship between what you see on the screen as the model is built and the final product. Then, the visual feedback you get from the screen during model-building can be to, say the least, limited. Most of the time your model will look like a cross between a bird’s nest and the Crab Nebula. Further, the mass of the model is always zero, and it may be difficult or impossible to verify key model dimensions until the last feature.

So, why use surfaces?

Well, there are times when nothing else will do it for you. Surfacing may simply be the right tool for the job. In the same way that you would reach for the Revolve when modeling a wine glass, or you would select a Helical Sweep when doing a screw thread, there are topologies and models that simply cry out for Surfacing, and if you can't do it you're in trouble.

So, the bottom line is that if you can easily get away using only Solids, by all means do it. If your part requires Surfacing, then get your learning hat on, or hire someone with experience.

When to Choose Surfacing

1. when there is simply no way to create the required geometry using solids exclusively. For example, most of the time when there is non-constant curvature in 2 directions.
2. when you use the Master model approach (External Merge) for assemblies – you can use solids but the approach is much more powerful with surfaces.
3. Want to use ISDX functionality which can produce surfaces of higher quality (higher order) than standard Pro/Engineer surfaces.
4. Very complex models: even though you may be able to create all of the individual features using solids, for some very complex parts, typically metal castings and plastic housings, it may be prudent to start out using surfaces in order to avoid having to rework the model later.

   When you’re very experienced – after a while surfacing just becomes easier and more intuitive than solid modeling. Its like learning a new language that's much more powerful and flexible than your old one. It just becomes second nature. Its now been years since I’ve used the ‘shell’ feature. There’s nothing wrong with it, it just doesn’t occur to me to use it.