Unable to split a simple closed solid polysurface


I don’t get why can’t i split a solid?

Yet if I move the cutting plane to certain point,it can split.

Any particular reason why it’s failing?

split.3dm (114.3 KB)

Thank you

I got it to work by exploding and joining the Brep first.

How did you build that form? I think this issue is related to these folded over control points on the side surface:

Yeah, I was using grashopper’s curve component. It takes 2 tangent vecotrs and I was adjusting length of each vector numerically. But why would it still be a problem, it’s mathematically “valid” surface, no?

Thats beyond my pay grade to understand.

Here’s how I would deal with it in GH:

It doesn’t split because it’s intersection is not complete and closed for some reason.


If you Explode the object and rebuild the edges, you can see that they are way out of tolerance.

The gap in the intersection curve corresponds with the distance between the rebuilt edges.

Something you (or Grasshopper) did while building the object forced the edges together despite the fact that they were far too far away from each other to be joined normally within the file tolerance.

There does seem to be a bug in Rhino’s reporting of the object, as before exploding and rebuilding the edges, it reports that the edges are within tolerance.

    Valid polysurface.
    closed solid polysurface with 6 surfaces.
  Edge Tally:
     12 manifold edges
  Edge Tolerances: 0 to 0.001
    median = 0 average = 8.33333e-05
  Vertex Tolerances: all 0

Do you have the GH file you used to build this object?

It does, I will get this on the pile.


Thank you. I also notice I got a report of object being a closed polysurface.

The original files are attached.
seat3.3dm (175.0 KB)
seat3.gh (24.4 KB)

So I did create a an object with GH, then baked it and applied CageEdit to modify a form a bit.

In addition, for some reason a surface split doesn’t like the surface either. No way I could get it trimmed. But that one is off-topic.

Thank you

That seems to be where things went south - the object baked out of GH is clean as far as I can see.
In the 3dm file, the edge tolerances are way off.

But normally, CageEdit… What are the good use cases for it? Or are there any recommendations using it “safely”?

Hi Alexander - - of course it should work - I am only poining out that that appears to be where it goes wrong - if you can describe exactly what steps you take after baking from GH, we can try to find the specific problem.