Hi Martin, also those little bumps are related to why ViaCAD cannot make a radius greater than 2.4 - what's happening is that the fillet is starting to kind of cave in on itself at the top. At radius 2.4 it's kind of awkwardly bunched together and at radius 2.5 or higher it becomes not just bunched but actually has a portion of it kind of inside out with a self-intersecting surface.

It's not unusual for various NURBS surface fitting mechanisms to begin to get unstable with little bumps and ripples when they start to closely approach that kind of self-intersecting state.

That same kind of thing can happen in MoI as well, but in some cases like this one MoI's filleting mechanism is able to detect that the fillet is going to be self-intersecting and it stops the fillet outside of the area where it would become collapsed and puts in a different kind of blend patch in there. It isn't able to do that in every fillet case but with extrusions it seems to work pretty well.

- Michael