This is a model of a Turk's head knot. ( en.wikipedia.org/wiki/Turk's_head_knot ) It is a 3-lead, 5-bight knot (3x5), with a triple strand. In the first file, I added a small base to the bottom to help with printing. Without the base, the 5 initial contact points tended to detach and the overhang on the bottom is pretty extreme.

The example was printed on a printrbot (thanks Mike!) from white ABS. It measures approximately 50mm in diameter at its widest point.

The knot path was generated via a Sketchup ruby script I wrote, and then the strand cross-section was extruded along that path. This created some very complex objects and took some work to figure out how to deal with overlapping areas and get a manifold object.

I have generated other lead/bight combinations, but this was one of the nicer-looking early attempts.

Edit: I added the Turk's Head .stl without the base, for those that would like to add support material, or try and print it without a base.