Surface Modeling Basics and Troubleshooting

 From:  Michael Gibson
4751.13 In reply to 4751.1 
One thing that I've noticed is that people coming from a poly modeling background have difficulty with thinking of trimming and cutting operations as a "first class" primary way to do modeling.

I'm sure that's because booleans just don't work very well in poly modeling and they're usually something that people have learned to completely avoid, and instead to construct all pieces of the model by edgeflow lines.

That's probably the biggest difference between poly modeling and NURBS modeling - in NURBS modeling trimming/cutting/boolean operations are usually actually the best way to get things done, so it actually is better to try to figure out if you are able to use them as the first plan of action rather than trying to avoid it.

You can use the freeform surface creation tools as well, but you generally want to use them to form large extended surface sheets and you usually should not try to directly surface all the final edges of your end model - instead many of those final edges should come from intersections and cutting operations, particularly things that have a 2D profile to them.

Once you get the hang of this, things can go very quickly though, because it is actually much quicker to build things in this way since drawing and managing 2D curves is easier than managing full 3D swooping stuff.

Not every kind of model is applicable to this kind of workflow - if your shape does not have any kind of 2D profiles to it then you'll need to use a more full 3D workflow, but even then you'll still want to try to build simple extended surfaces and you can cut those surfaces with other 3D surfaces rather than curves, it's just easier when you are able to use curves directly.

If your model does not really contain any kind of shape in it that you can identify as the full underlying form that is then cut, then that's the kind of model that's better done with poly modeling tools instead - think of stuff like an ear or a nose or something like that - those work better with poly modeling tools.

But for mechanical or man-made shapes that often manufactured by having pieces cut out of some larger initial stock, the NURBS workflow can produce that stuff really quickly (and also more accurately) than poly modeling, but you basically need to approach it in almost the same kind of way that it's actually built - try to think about making "pieces of stock" like a big sheet or a block that will then have some areas removed to make the final shape.

- Michael