Boolean difference creates open looking polysurface


Here’s an example of Boolean Difference not working the way it should. When I try to subtract the box from the knot pipe I get an open looking polysurface, even though Rhino says it’s closed. If it was a single case I would fix this surface with Dupfaceborder, Curveboolean, Planarsurface commands. But I’m trying to create a grasshopper definition that does this for several cases, so then it gets harder to automate that. And in the end it’s Rhino not giving the correct solution, or am I doing something wrong here?

I checked Rhino 6 Beta and it does the same…

171108 Boolean difference issue.3dm (430.4 KB)

Oh some extra info:
I created the shape by drawing a line in 2D and using the pipe command on it.

I believe the problem is caused by the pipe being self-intersecting. I could replicate the same problem by trim & cap. I would try to split the pipe into segments and then boolean them together to create the same geometry with already solved overlaps. That might work out if it’s not too much work for you.


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Thanks for your reply. I might try splitting the curves at their intersection point before piping and see if that solves it for now.

Yes, as Jonish said, problem come for self intersect.

just split your curves in 3 parts, then apply piping with round cap, and make Union of these 3 pipes.
Edit : Also work by just splitting curve in 2 parts.

171108 Boolean difference issue.3dm (1.2 MB)