Hello all!
I am having difficulty cutting a closed polysurface in half. I have tried running a split on the polysurface, when that didn’t work I tried ungrouping it and splitting it again - this also didn’t work. I have overdrawn my split line to ensure that it isn’t an intersection issue, still no luck. Any ideas would be greatly appreciated, thank you!
I think it’s because your cutting plane is hitting the singularity on the apex of that sphere. Maybe you can try to cut the sphere using its own isocurves?
If you would post the file, you’d get better answers. 
Sorry I am really new to Rhino and am not certain what you are referring to. I have tried splitting it on the x axis as well as on the y axis and neither worked.
I think Sericanus was correct about the singularity, but it’s on the bottom surface, which was a revolved surface. Remove that surface and cap the remainder, then it splits fine.rhino problemck.3dm (368.6 KB)
rhino problem mod 1.3dm (319.7 KB)
Seems like the bottom surface is the culprit since the cutting plane is running through its “singularity” point and rhino just gets confused. If you replace it with a surface from planar curves you’re good to go.
That worked, thank you so much guys!
Woops you’ve already got it.
