Boolean - which one is the same as AutoCAD Subtract?

Boolean - which one is the same as AutoCAD Subtract ?
I have 2 closed solid polysurfaces, which are somewhat like cylinders. One is completely inside the other and I need to Subtract the inner from the outer leaving a cavity fully enclosed.
Using BooleanDifference, it errors and says “Objects do not intersect. Nothing done.”
I also tried using OffsetSRF, Flipall inward, 1 inch (my outer cylinder is only 1.25 inches, so that should have made things solid
What am I missing ? Is my solids not solid so the outer never touches the inner ? How to fix ?

Rhino does work with hollow solids which have inner and outer surfaces which do not touch. It is possible to create such an object in Rhino and export it but there is not much you can directly do with it in Rhino.

What do you need to do with the object? There are ways to work with two distinct surfaces which are equivalent to a hollow object.

Hi - I really need to get 2 solid polysurfaces to be subtracted from one another leaving a enclosed cavity. Both polysurfaces are not uniform, but I tried to experiment by just placing a smaller closed cylinder inside a larger closed cylinder, but found that unless one used exact wall thicknesses that were less than half, it fails, but in my case with odd shaped cylindrical cylinders there is no uniform wall thickness to get to the center.
Bottomline: I need to Subtract an inner object from an outer object that never touch each other, leaving an enclosed cavity.

What would you do with the result if you could create it? Someone can probably help you with how to get the final result you need using Rhino, but it may be a different set of steps than what is done in other software.

Hi David, I guess I am to understand that Rhino considers a solid box to be hollow, as opposed to a solid box in AutoCAD, nanoCAD or progeCAD, which consider such to be a solid like an ice cube.
Basically I extrude a 2d object, in one dimension, then I loft through it with ellipspes and circles and such, then I create an outer box.
By subtracting the loft from the box, then subtract the box form the extrude, the extrude is now sculpted.
Any help would be appreciated.

Rhino essentially considers a closed surface or closed polysurface to be “solid” for volume calculations, Boolean operations, etc. Rhino does not use the concept of “hollow”. I understand what you want. My question is why do you want it?

What is the next step with the object described above? Calculate a volume? Perform Boolean operations with other geometry? Output to other software? ???

For example you may want to put a hole in the object using Boolean difference with a cylinder. In Rhino with a separate outer and inner closed surfaces that can be done by:
Boolean difference the outer surface with the cylinder.
Boolean difference the result of the previous step with the inner surface.

For the volume of the hollow object first calculate the volume of the outer surface and the volume of the inner surface. Then subtract the volume of the inner surface from the volume of the outer surface.

To export the hollow object to other software use NonManifoldMerge followed by CreateRegions as described in the link above.

What do you want to do with the hollow object?

It will sculpt the extrusion. Next is 3d printing. Thanks for the thoughts. I think I will thicken the loft and subtract, which should work.

Another thought I had was to instead just thicken the LOFT by .5 inches, which would just cover the EXTRUSION, then BooleanDifference away the LOFT, leaving the sculpted EXTRUSION. Unfortunately the closed polysurface LOFT has a bunch of errors and naked edges, after OffSetSRF, which it did not before.
Is there another command that will thicken ?

…Using OffsetSRF and selecting Solid=Yes, creates an open polysurface, when it should create a solid ???
I think part of the problem is that OffSetSRF does not know how to handle a inner elbow type of offset, where surfaces will bump into other surfaces as they swell up.

so if I thicken a closed polysurface it creates an open polysurface, so to JOIN the 2, I need to uncap the closed polysurface.
How do I uncap a closed polysurface ?

Well if it’s for that reason, then you don’t really need to ‘do’ anything, do what was said about a nonmanifold merge. Of course for 3D printing you don’t actually need the interior, the slicer settings will handle wall thicknesses and infill.

Why is this taking son long? I will not read the entire thread but just suggest to:

  1. Upload your model

  2. Upload pictures of what you want as a result.

  3. Try commands such as BooleanSplit and BooleanDiffefence