Hi Alexander, so the problem area of your model is in this area:



If you zoom in closely to that area you can see that there are some microscopic little surface fragments there, and it appears to have some pieces stacked up right on top of each other there:



That kind of messy area will be difficult to get a clean offset from - the offsetter will actually try to offset those little micro slivery surfaces, and try to extend them and intersect them with neighboring surfaces and stuff like that.

You really want to have a more simplified and clean model structure in order to get a good shell on it.

One thing about filleting is that you usually want the pieces you are filleting to come to more of a sharp angle and then let the filleter produce the rounded shape. In this case you've tried to make the initial surfaces come be smooth to each other, but you can see that this actually makes the filleter's job harder because it makes for a little tiny sized fillet surface when it tries to smooth out that area that you made pretty close to being smooth initially.

So that's one thing to make a better model - don't make part of the surfaces come close to being smooth to one another to start with if you want to fillet them.

Then another tip for shelling is you may want to apply the fillets _after_ you do the shell instead of applying them before. When you apply them before it means that the fillet surfaces are then some more stuff that need to be processed during the shell operation as well.

So that's what I'd recommend for this model - do you have a version of it before you applied the fillet? If so then try shelling that first, and then apply the fillet after the shell.

Also to get a proper fillet you may need to not have the initial surfaces come close to being smooth to one another as you have done here.

- Michael