At Gathering 4 Gardner, Colm Mulcahy suggested I try the following 3D-printing project.

Recall the "napkin ring problem": Take a sphere of radius r and drill out a hole along a diameter so the remaining shape has height h. Then the volume, V = πh³/6, does not depend on r.

He thought that if we print these shapes as solids (i.e., with 100% fill), they should all weigh the same. See the following post for the results.