I was wondering if someone might know the reason for these errors when trying to fillet the edges of this open polysurface?
You’ll see the problem when you fillet just one inside edge. There are a few ways to finishe this corner. You can blend these edges and trim the surfaces.
Delet what’s not needed and then use sweep2
One qay to avoid this problem is to create the rounded square hole in the center with a degree 3 curve like this here:
Note the vertical surface is one surface and not a polysurface.
20_10_25_fillet_problem.3dm (489.6 KB)