This knot has a special property: No matter how the knot sits on the table, it never touches the table in more than two places. This makes the knot rock back and forth easily, and roll down even very shallow inclines. It's a fun thing to have on your desk and makes a nice intro-to-3d-printing gift. Files for both thick and thin versions are included here.

For very detailed information and instructions about this object, see MakerHome, Day 110:
http://makerhome.blogspot.com/2013/12/day-110-rocking-knot.html

UPDATE: kitwallace has developed a way to use OpenSCAD to make closed parametric curves such as this one, and this OpenSCAD way fixes some meshing problems at the join point; see "Rolling Knot" at http://www.thingiverse.com/thing:230557

MORE UPDATE: kitwallace has improved even further and written a very nice post about the journey: http://kitwallace.tumblr.com/post/74713917178/openscad-revisited

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