Hollow Knotted Gear

The green knot revolves twice, making three full rotations along the way. It forms a rectangular cross section and a triangular hole.

The blue knot revolves three times, making two full rotations along the way. It forms a triangular cross section and a rectangular hole.

The two knots fit perfectly together, and only orbit each other by moving together.

Inspired by Oskar van Deventer's original Knotted Gear: http://www.shapeways.com/model/11915/knotted_gear.html

The first few rotations of the knots will feel a bit rough, but once you gently rotate them ten to twenty times, they smooth out. Also, the knots rotate much easier in one direction than in the other.