Hi plish - part of the Inset process involves calculating offset surfaces, and with a kind of chaotic surface like you are showing there with a lot of little bumps and wiggles it makes offset surface creation very difficult.

Part of the process of Inset involves doing offset calculations of the "side walls" around the inset face.

Basically an offset surface is a new surface that is created by tracking along the surface normal by a particular distance. It's sort of like sticking a pole on the surface and moving it around and making a surface tracking along at the other end of the pole. When you have a lot of little bumps and wiggles in a surface, you can imagine that the movements of the "end of the pole" become magnified, and it's easy for the result surface to become self intersecting. Once that happens it will then cause further problems because surface/surface intersections will have problems when self intersecting surfaces (surfaces that fold back and forth over themselves) are involved.

So the geometry that you have there with lots of bends and wiggles in it, is just generally unsuitable for anything involving offset calculations, so probably anything under the Offset set of commands (Offset, Shell, or Inset) will not be functional with that kind of geometry. You will need to create cleaner and less wiggly geometry in order for Offset, Inset, or Shell to really have much of a chance of working at all.

Just in general NURBS modeling is not good at making shapes with lots of little lumps and wiggles in it. If you need to do stuff that's shaped like that you would be better off using a polygon modeling package instead where you can do sub-d modeling, those programs are more focused on making organic shapes. MoI is much more focused on making sort of smoother semi-mechanical type shapes.

It is possible to make lumpy/bumpy/chaotic shapes for some purposes, but just as you've seen here there will be many areas of the toolset such as offsets and also booleans (when you have self-intersecting surfaces) that will not be usable with such geometry. That's a generally expected consequence of that kind of geometry.

- Michael