Hi OSTexo,

> Am I missing something obvious to prevent this behavior? Thanks.

Well that's probably the single biggest problem currently with MoI's filleting mechanism, it won't sort of cross over past an edge like that so a small fragment of a seam can limit how far you can do an edge fillet.

It's unfortunately not an easy issue to me to fix, at least in a short timeframe.

If you notice that your seam on a tube is not good, you can rotate your generator profile curve by 90 or 180 degrees and then reconstruct your surface, the seam on something like a tube will be inherited basically from the seam of the initial closed curve.


One other thing that you can do is to separate things into individual surfaces, and then do a surface/surface fillet which is when you have 2 individual faces selected. That does a different style of fillet calculation which does not try to trace along the edge structure like the edge-based fillet.

So for example in your shape there if I separate out things into individual surfaces, and then select these 2 individual non-joined surfaces:



Then I can perform a surface/surface fillet that can go a further distance and is not limited by that seam edge or other surface fragment:



That can help to construct a fillet that the edge filleter cannot do, but the edge one tends to be more convenient since it can build corner patches where multiple edges collide, the surface/surface filleter does not do corners and may need to have some manual trimming done after the fillets are generated (but not when it forms a simple closed shape like here).

But before doing that surface/surface fillet, I also needed to do one cleanup set on your tube part as well - the tube fragment here:



Is part of a larger surface that has some bunched up areas that are places where the surface kind of folds over itself in a self-intersecting manner:




That kind of self intersection is pretty bad for a lot of operations, it will often time mess up booleans as well as fillets. It's the same issue discussed recently here:
http://moi3d.com/forum/index.php?webtag=MOI&msg=2728.2


In this case, the active area of the surface is ok though, so applying a "ShrinkTrimmedSrf" (which you have to either type in or set up a keyboard shortcut to activate) will solve it by shrinking the underlying surface to the trim boundaries and actually removing those bad bunched up self-intersecting areas from the surface.


Unfortunately fillet as you've seen is a very sensitive function, it performs quite a lot of intensive calculations, including stuff like creating offset surfaces, calculating surface/surface intersections, making extensions and trims. It doesn't take that much irregularity in the geometry to mess up any one of these steps.

- Michael