Yes, singularities are a problem, but even though this may work in NX, doesn’t mean it will create good geometry. In this case I would simply avoid having singularities to begin with. Check out the file included with this post, it has my approach to something like this.
-First, I brought everything back to theoretical sharps.
-Next, I split the tapered faces with isocurves matching up to the edges of rounds in the rectangle portion.
-Used BlendSrf to make the blends (yellow surfaces)
-Created a couple BlendCrv and used Sweep2 to create the orange surfaces.
-Finally I used XNurbs to fill in the small green corners.
p.s. You can also use NetworkSrf, or Sweep2 and MatchSrf to do this, but I have XNurbs and it’s just faster.
The shell does fail, but this is not a surprise because the rounds will collapse to zero or less than zero when you offset this. I didn’t want to spend the time, but I would use OffsetSrf to offset the main shape with theoretical sharp edges and blend it with the same steps as outlined above.
. Fillet edge and shell problem_Mark.3dm