Summary This came of watching Brun's video on YouTube (I highly recommend his channel): https://www.youtube.com/watch?v=AuS6HDHc7XE Turns out (not a pun) this is a classic puzzle presented to machinists: https://www.cnccookbook.com/how-to-make-cnc-turners-cube/ The challenge in this exercise was in trying to come up with a model suitable for 3D printing. Approached this as first as might a machinist - carving out cylinders from the nested cylinders, but quickly realized the inside surface of the cubes was not ideal. Had to bump up my CAD game, slightly, to get a spherical inside surface. :) This is in fact a superior result practical with 3D printing that is not practical with subtractive manufacture. There are other (inferior) examples of the puzzle on this site. Either the inner cubes are not free to move, or the interior of the cube is not a sphere. (Some guy with a fancy CAM lathe might prove me slightly wrong. Perhaps my nephew.) How I Designed This Designed in OnShape https://cad.onshape.com/documents/7578e4f3ee04d5c50b0f9ba6/w/8a71c61a2a394945cbf93649/e/0664345b59a74f88c0c675d9