Have us print this for you
PLA from £6 inc. UK delivery on letter-sized prints. We slice, print on a calibrated Creality K2 / Bambu A1, QC and post.
A friend who is into puzzles pointed me at this 3D puzzle http://www.cs.tau.ac.il/~efif/applications/puzzles/knot/ so I whipped it up in a few minutes in OpenSCAD.
If you get stuck, there is an animation showing the solution at http://www.youtube.com/watch?v=xNtNQRTdxps
