Hollow closed polysurface

Hello everyone, i am trying to create hollow domino stones but cloudnt make it. When i try to do it , they turn regular polysurfaces within each other rather then create 1 hollow polysurface. Here is a video to illustrate the problem.

Screen Recording (10.05.2021 13-10-12)|video

Hi @karakusc
Usually this type of non-manifold geometry is not allowed in Rhino, but you can force it into existence by selecting the inner and outer shell, running NonManifoldMerge followed by CreateRegions and then delete the inner shell.
HTH, Jakob

hey, that worked like a charm! I didnt see any naked or non manifold edges on the geometry but i want to ask you if that would cause a problem in the 3d printing or any future boolean operations. Thank you!

Hi @karakusc
IIRC any booleans will “delete” the inside, since it’s basically just a trick convincing Rhino that those 2 shells are to be regarded as one - something that isn’t normally allowed in Rhino. As for 3D printing, it depends on the printer and the technology used (FDM, SLA, SLS etc.) and the slicer/software used. Some slicer software can add the shell thickness for you, others will accept seperate meshes as long as one is fully enclosed by the other, some need the two (or more) meshes to be joined as disjoint meshes. If your end goal is 3D printing, I suggest you talk to your supplier/print tech guy.

Thanks for your reply, it is more complicated then i expected but i think i will be okay. Thank you very much!

Another way out, if, eventually, a mesh is what is needed, is to mesh both objects, Flip the inner one’s normals to be pointing in and then Join the two meshes into one disjoint mesh, which is allowed.


Hi pascal, thank you for another answer but i used the first method and do boolean operations on it and export as both stl and stp and it seems fine to me. Here is the picture of it and i also attached the file:) Thanks for all your help!

hollowed.3dm (979.4 KB)

Hello - once you connect the inner and outer shells with a set of faces that touch both, the problem goes away anyway…

Union the cutter with the inner shell
Difference the result from the outer shell.


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Thank you very much!