A few years ago I made a mechanical puzzle for a friend, with 5 aluminium rings around a cylindrical aluminium core. Each ring had a pin protruding from the inside that engaged in a slot in the core and all each ring was joined to its neighbours so that each could rotate independently but all had to move along the core together. The aim was to remove the core by twisting the rings and it was just a case of mental Continue reading Puzzle number 2 →