Hi Rodney, from what you described, that will likely be a pretty complicated fillet to calculate.

A couple of things you can try - first you will probably need to use a pretty small fillet radius value for it to be able to fit in there. If you have a value that will create a fillet that is too large to actually fit in the available space, MoI will still try to calculate it anyway but it can potentially make a chaotic result that may be taking a long time to calculate. So try starting with small values maybe like 0.05 and going up.

Another thing that can make things more difficult for fillets is when you have surfaces that come close to being smooth to one another but are just a bit slightly non-tangent instead of being smooth. I haven't taken a close look at your curve yet, but if was made out of segments that were almost smooth but not quite tangent to one another that could make things harder for filleting.

Also you may want to make a larger single surface instead of a segmented one made up of joined pieces. You can do that by fusing together segments in the original curve by deleting the control point where 2 segments touch each other.

But you are probably looking at a pretty difficult fillet case there, fillet by its nature has to do a lot of complex calculations such as surface offsets, surface/surface intersections, extensions, etc...

- Michael