Super hack to create hollow objects for 3d printing in Rhino
This is a quite easy “hack” how to create hollow objects that are usually not allowed by other CAD programs. Great for 3d printing. Simply connect the outer and inner objects via some random pipe or box, then join everything and untrim the hole that connects them with the ! _Untrim tool. You will notice that the two original separate objects now appear as a single object instead, despite the lack of an actual connection in-between.
An alternative way is to select both objects and use the following commands: NonManifoldMerge, then CreateRegions, then delete the region you do not want, such like the core inside the sphere in this particular example.