Wooden Knot Cross Puzzle, OCC, Three Pieces, Kong Ming Lock

thingiverse

This is a simple yet fascinating cross knot puzzle of three interlocking pieces, whose design may have originated in China during the time of Zhuge Liang (also known as Kongming, AD 181-234). Easy as it appears to be, this puzzle requires a bit of planning in 3D design. One must make sense of the physical constraints. While the length of each piece is largely arbitrary; its width has to be exactly three times as much as its thickness. Moreover, one must consider the tolerance. This makes an excellent entry-point 3D design project for STEM teachers and their students. Yes, a bit of struggle is indeed healthy! In the current design, I have added a 0.5mm tolerance to the OCC slots and a 0.25mm tolerance to the opening so that children can slide them back and forth smoothly. There are two styles with various widths and lengths available for fun. One way to adjust the tightness is playing with the resolution - starting with say, 0.18mm. If it is too loose, go to 0.2mm. If it is too tight, go down to 0.12mm, etc. It depends on the printer. References: 1. https://en.wikipedia.org/wiki/Burr_puzzle 2. http://chinesepuzzles.org/interlocking-burr-puzzles/ 3. http://www.mathematische-basteleien.de/devilsknot.htm