Seen many of these sort of things over many years, so decided to make one myself. I used a cone to cut away the unwanted portions of the spheres I used for the rings, so as to widen the rings while retaining access to the centre rings and sphere. Decided 7 rings plus centre sphere was enough for me. The  cone cutaway also means the rings can be tighter and less able to be disassembled. I used supports, though i dont know if it would be feasible to do without.  I'm very new to 3d printing and Blender.