Difficulties adding thickness on the inside of a polysurface


I’m pretty new to Rhino and I can’t seem to solve one issue.

I have created a closed surface (see picture below) and I want to add a thickness to it. When I’m trying to offset the surface it is not created parallel to the ground plane (see picture below). I need it to have the same thickness in all cross sections if you look from above, in order to 3Dprint). I also tried to close the curve to a solid and then shell it but that slightly changed the round shape in the bottom. Extrudesrf doesn’t work either as well as using the tool thickening on the surface.

I hope someone can help me solve this, thanks in advance!

Hello - if I undertstand your question… the thickness that matters in not necessarily in a horindal plane - if you offset a sphere, the horizontal sections will vary in thickness, thicker at the top and bottom, only ‘accurate’ in the middle. It needs to be to mantain an acual constant wall thickness. Does that make sense or am I missing the point?


I think you can get your desired result by duplicating your object and using the _Scale2D command. Set the base point to the center of your object and use a scale factor slightly smaller or larger than 1 (0.95 or 1.05). You may need some trial and error with the scale factor to get the desired thickness.

Edit: this will not meet your requirement of “same thickness in all cross sections”.

How did you create your original surface? If it was created with the _Loft command you could offset your original curves and create another loft surface.


Hi, thanks for the fast response!

Yes, that’s exactly what I need help with. It needs the same wall thickness as I’m going to 3D-print it. When I try to offset the surface 1 cm (my desired wall thickness) and I make it a solid, holes are created when I open the obj-file in PrusaSlicer. See pictures.

Hi, thanks for your response!

Yes as you said, I need the same wall thickness so scaling won’t work.

I created the surface with three closed curves and then the _Loft command

I tried to do as you suggested, to offset the curves and create another loft but that also gives me different thicknesses. I guess that’s because the seams on the lofts aren’t located on the exact same spot? Or is it something else that creates my problem of uneven thickness?

So not sure how to proceed…


I now managed to move the seam so they’re aligned so when I slice it in PrusaSlicer I don’t get any holes, however, there’s still a slight uneven thickness. Is there anyway to solve it so you get the exact same wall thickness over the whole model so I don’t get any gap fills when I print?

How about _shell ? Would that work?

I tried that as well but it doesn’t work… This is my result then:


I can appreciate that you want to understand how to get the thicken results in Rhino if possible.
If you simply want to get this done without the troubleshooting, Meshmixer (free) can give a a fairly good thickened result from a mesh, and can be more forgiving of geometric issue where using a nurbs surface would likely fail, perhaps requiring modifying the nurbs geometry, which may be undesireable.

Hello - what I was trying to point out is that the same wall thickness is not the same as having the same thickness in horizontal slices. The printer need not , in fact cannot, lay down slices that have the same width to achieve constant wall thickness:

Does that make sense?


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