Can't cut nor cap this extrusion

[René_Corella]

True I actually projected to Cplane before rebuilding the curve (redundant step) and it worked - I have faced similar planarity issues in the past:

Region union not working

Hi all, I’m trying to combine two closed planar regions existing on the same plane in 3D, and it doesn’t work. If the same curves are reoriented to the XY plane then it works. I also tried this with basic co-planar curves (two circles) and no ‘optional boolean plane’ seems to yield other than rhino plane. Any ideas or is this some bug? What am I missing? Thanks! [image]REGION_PROBLEM.ghx (197.9 KB)