Four Triangle Puzzle

George W. Hart

Other Puzzles

This puzzle is composed of twelve identical components, which assemble to form four triangles that each interlock with the other three to form a hollow, snug, spherical form. It is harder than it looks. Geometrically it is based on the "orderly tangle" of four triangles first described by Alan Holden. The idea to use lap joints and make a puzzle from it comes from Teacher Lin and Sculptor Wu. For background on its mathematical structure, see this paper.

Here is a nicer version of the same design, produced by Kathleen Malcomson from dimensions I provided. Robert Sandfield had the idea to include the ball at the center and used it as an exchange puzzle at IPP 26 in Boston. It (with a wood ball, not steel as in the image) may still be available from Kathleen Malcomson.