In the attached I have a closed curve made by projecting a 3d border into 2d.If I try to OFFSET outwards 5/32" I get a selfintersecting open curve. I thought I would share before I move on.
Problem Offset.3dm.zip (12.0 KB)
There are small arc sections in the upper corners. The length of those arcs is 0.0025 and the absolute tolerance is 0.000977. Make the absolute tolerance smaller and offset should work properly. The absolute tolerance should be an order of magnitude or so smaller than the smallest feature.
What I did to move on was to delete those segments and fillet to close. Should Rhino create something crazy because of this?