Clingstone-Freestone came to me in a flash of inspiration, a fully-formed idea for a puzzle that could be built to resemble a ripe peach with a wedge cut out to expose the stone. It seemed like a nice idea, but would it work? Yes, it worked on the first try...but no it didn't turn out a good puzzle.
The premise? The inner sphere must be correctly positioned to allow two halves of the outer sphere to move freely. Then the two halves would un-hinge to rotate apart around an axis located un-intuitively at an imaginary point on the missing 'slice' of the outer sphere.
Cast Marble or Vesa Timonen's Tangerine puzzle.
So far, the mechanism seemed to work perfectly on the first (and only) prototype I built. But the whole premise has an intrinsic flaw....