Can not union two polysurfaces

Every time I try to boolean union those two polysurfaces, nothing works and when I export STL file, this lower part disappears in Meshmixer when I try to make solid.
Any suggestions what to do?

Hello - it is not possible to help without a 3dm file to look at. Please post it here or send to



Many thanks for the reply. Here’s the file

Rhino.3dm (1009.5 KB)

Hello - Cap the lower object to make it a solid then BU. However, you can also remove the caps on the upper object (ExtractSrf and Delete) then simply Join.


BU works now. I’ll see if STL file works as well.
Thanks again

It works. Thank you very much

One more question about same problem. How to join or boolean mesh and open polysurface? Or how to cap polysurface with curved edge?
Here’s the file

Eye.3dm (1.7 MB)

Hello - you can’t really combine the two, you need to make them the same thing - either meshes or surfaces. Since it is easier by far to get meshes from surfaces than the other way around, I’d convert the ring to a mesh and work from there. I’ve attached something that might do- it’s a closed mesh, however in the orignal ‘eye’ mesh there are (tiny) self-intersections which may or may not cause problems in printing. I’d say probably yes.

I’ve added a couple of section curves that show where there are self intersections.
I’ll explain the process of combining at some point. Remind me if Monday rolls around and I have not done it yet.

Eye_PG.3dm (6.0 MB)


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Many thanks.

Reminder for explaining the process, how to combine mesh and polysurface.
Because, I’ve got this very problem over and over.

I export STL file from Rhino and in slicer shows that the object is hollow, not solid.

Pieta.3dm (1.0 MB)

Guess it won’t work in Rhinoceros Corporate (64 bit). :disappointed_relieved:

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Pascal Golay, first of all, thanks a lot for your time. I tryied to find the way how to make solid the hollow object, in vain thou. Please, if you have free time, help me to solve this problem.
Thanks again.