Hi John, there are a few things in your shapes there that are not conducive to good filleting.

Probably the biggest one are these very tightly curved corners in these areas:





When you have a tight bend like that, it will limit your fillet radius to a small value that is smaller than the radius of the bend.


Here is another way to kind of visualize what happens with a fillet trying to go around a tight bend like that.

If you have a bend here, imagine that the line in the lower-right is the distance of the fillet radius that you are asking for:




Now if you watch as that fillet radius moves across the tight bend, it causes a messed up area of self intersection:




So to make something fillet friendly, you don't want to have tight bends in small areas, instead those need to be an actual sharp edge there.


If I draw in a line like this, and use boolean difference to slice off those little curved corners:



Then you can fillet the top edge quite a bit more, up until it starts to eat up all of the edge surface below it, here is one at radius 0.2 (using MoI v2 beta):




The lower edge has a different problem - that one is probably just not going to fly trying to do it all in one piece due to the area at the end here where the 2 surfaces on either side of the edge are totally flat and tangent to one another:



That would cause the fillet to be totally erased in that region - MoI's fillet engine does not handle that kind of fillet situation very well where the fillet disappears to nothing along some stretch of the edge.

You would need to get that to have some angle in there to make it filletable, or hack off that piece so that you could try to get a fillet along the other regions where the fillet does not have a "disappearing" region to it.

- Michael