Hi Ron, well a lot of the problem is that the geometry library that MoI uses just doesn't have a particularly robust shelling mechanism in it, it can get confused pretty easily if different areas would end up needing to collide into one another.

If you know in advance that you're going to want to shell something that will cause something like a fillet surface on the outside to totally be consumed away you would probably want to do the filleting after the shelling rather than before.

If MoI's sheller fails for your part, really the best thing to try to start with is to import your model into a different CAD system like ViaCAD which is also pretty inexpensive and see if it will shell it as-is without needing to do any reconstruction.

- Michael