3D puzzle: Twisted half cube with a sphere in the middle

thingiverse

A spiral cuts through a cube with a sphere inside. It splits it into 4 pieces that can be screwed into one another. But there is a cylindrical hole that lets you turn the two half spheres. You have to put it into the right position if you want to unscrew it. I saw it in the pocket of (the fantastic) Colin Wright https://mathstodon.xyz/@ColinTheMathmo and he told me it's called Hanayama marble. The one I saw is a very polished metal thing, if you can buy it, don't print it!I designed it using onshape https://cad.onshape.com/documents/ddc8cd6d77f624b674a11f96/w/299f438ab6ad5e302cb043ed/e/b9b35d981d54987bc01026ebI actually sliced the two half-spheres in two pieces for easier printing. Don't hesitate to shrink by 3-4% (making a 96% scale) on the half-spheres for it to move freely.When hollow, supports are needed, spheres are not that easy to make properly. Put them on the round part, not the empty one. PLA is good, PETG was not that nice.I made another version, turning a full twist (in black) while the yellow-blue one is ¾ of a twist. I had to make the cylindrical hole along the diagonal. I made another one with 3/2 of a twist. The cylinder is then better along the screw axis. Beware to take the 97% reduced sphere model or else it might not rotate inside!