Boolean 2 shelled Solids Yields 2 Solids


  • I have 2 shelled, closed solids that are mirrored and with an overlapping face - when creating a boolean union I get 2 solids - an ‘inner’ solid and ‘outer’ solid instead of one solid that is shelled i.e. hollow on the inside. I’m doing this so my piece uses less material for 3d printing - to reduce the cost.

Anyone have any tips on the above? I’ve tried a variety of techniques and rhino keeps creating 2 solids as opposed the one.

Thanks, Andreu

Hi, you don’t actually need to do this in your model for printing, the slicing software can control the wall thickness.

That said, it can be done. If you make a shelled object that gives you 2 totally separate objects,’ Rhino normally considers that “bad” geometry, “Non-manifold” is the name of the error, but for the STL you can simply create the mesh from your model, then use Flip on the interior object so that the slicer will interpret it correctly.

Thanks Jim - I did some more searching in the forum and found this explanation:

" You cannot directly create “disjoint” solids in Rhino - it’s a somewhat philosophical limitation currently. If you select your inner and outer pyramids and run first _NonManifoldMerge , then _CreateRegions on the result - you will get two objects - one will be the hollow pyramid you want, the other will be the inside volume, which you can delete. It is likely that this object may end up falling apart into the original two volumes if you do certain operations in Rhino with them - as Rhino is not really designed to work this way."

  • This did the trick and more importantly I understand conceptually want Rhino was doing…

Thanks again, Andreu