Hi shayne - it looks like in your example there you've got an ellipse for the rounded shape?

That works great for something that meets at a 90 degree angle like that particular case you are showing there, but I'm not sure how it would work in the more general case of surfaces that meet at other angles to each other.

See here for a description of that problem:
http://moi3d.com/forum/index.php?webtag=MOI&msg=2259.12

Also since it's kind of unusual as far as these things go, as far as I know the geometry library that I use to calculate the fillets does not support that style of fillet creation - another thing that's a lot more difficult than just the simple case you are showing there is when multiple fillets collide into each other and corner patch pieces need to be calculated to glue them together smoothly.

So I mean I guess it could be possible to make a special fillet that only worked when filleting just one edge of a box like you are showing there, because that special case happens to avoid these various issues, but then that would probably confuse a lot of people when they tried to use it in a whole bunch of other non-box situations and it didn't work properly on anything else other than a box...

- Michael