Create a box and scale-it with respect to its centroid. Then use boolean to remove the smaller box from the bigger box.
Hello - use
NonManifoldMerge for this. The inner box will not have inward pointing normals though -you can use two mesh boxes, flip the inner one inwards and then
Join the two. Meshes can be disjoint, breps generally not, in Rhino.
Thanks for the explanation @pascal
Or wait for mcneel to release Rhino4d
Oh, I thought that was called Bongo.
Not the time variable but the 4th geometrical dimension