Hi LM,

re:
> Do you know what the difference is between those two? My original model, and one recreated with Shell?
> Visually they look pretty much like the same thing.

Well in the shell model the "side walls" are basically a loft while in the original they were trimmed pieces of spheres.

I'm not exactly sure yet why your original version won't work, but it seems to be failing to trace out the fillet rails properly.

It seems to be a bug when processing these particular surfaces. I tried with making 1.1 times larger sphere cuts and that one worked ok too.

So I don't think it's illustrative of some kind of general case that you would try to avoid.

Also if you run ShrinkTrimmedSrf on your original object it will do the partial chamfer ok too. Select the object, type the Tab key and then type ShrinkTrimmedSrf and push Enter. That makes the underlying surfaces of the side walls to be smaller pieces of a sphere instead of being full spheres.

If you run into fillet troubles it can be worth a try to run both Merge and ShrinkTrimmedSrf on the object and try again.

- Michael