A seven piece puzzle which assembles into three sizes of tetrahedron. The basic piece is made from five rhombic dodecahedra, and comes in two mirror image versions (orange and yellow in the photos). This piece is the "tetrahedron building block" (TBB). Easy: take one orange and one yellow TBB and build a small tetrahedron (order 3). Moderate: take two orange and two yellow TBB's and assemble a medium tetrahedron (order 4). Difficult(ish): take three orange and three yellow TBB's, plus the red piece and assemble a large tetrahedron (order 5). All these puzzles have a unique solution.
The unusual shaped pieces take some getting used to. But after you play with them a while, the three challenges will probably not seem difficult. The base plate is optional but may help with learning how the pieces can pack.
An "extreme" challenge, if you want to print out the extra pieces, is to take 12 yellow pieces and 12 orange pieces and build "the Great Pyramid" (a tetrahedron of order 8). This puzzle also has a unique solution, and is probably too difficult to solve by hand.
Curiously, tetrahedra of orders 6 and 7 cannot be made from tetrahedron building blocks because the number of rhombic dodecahedra is not a multiple of 5. It is not known if any tetrahedron above order 8 can be formed exclusively from tetrahedron building blocks.
No supports are needed. Each piece has been cut in half. Print six copies of the Left (half), six copies of the Right (half), and two copies of X5 (half).
The halves are then glued together with superglue. Each piece contains holes for alignment. After cleaning the holes out (if necessary) take a scrap piece of 1.75 mm filament. Insert the filament into a hole and cut it off such that about 4 mm is sticking out. After each hole has a piece of filament, fit the other half in place. If the fit looks good, remove and glue the halves together.
The pieces are made from 2 cm rhombic dodecahedra.
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