There are two polysurfaces in the attached. Neither will split the other despite having clear overlap.
Problem Split.3dm.zip (91.6 KB)
Rhino doesn’t make the intersection where the two curved surfaces become tangential at a vertical edge, here:
This is a known problem scenario in Rhino.
If you tweak the curve used to extrude the flatter piece by moving one control point a trivial amount so the arrival isn’t tangential then the split works:
Alternatively, you can create the two intersection curves and connect the gaps (maybe tidying the wobbly ends first) and use that to split the surfaces.
HTH
Jeremy
Observe the curvature graph. One CP is too far out. If you do what @jeremy5 suggests, pulling it in, splitting/trimming works.
