This project began when I read the following entry [#274] in Volume 1 of Popular Mechanics’ 1913 The Boy Mechanic:
The round lead weight for shot-putting or hammer throwing can be cast in a hollow cardboard or pressed-paper ball, sold in department and toy stores for 10 cents. Cut a 1/2-in. hole in the ball as shown in Fig. 1 and place it with the hole up in damp sand and press or tamp the sand lightly around the ball as shown in the section, Fig. 2. Cover over about 1 in. deep. A wood plug inserted in the hole will prevent any sand falling inside. When the sand is tamped in and the plug removed, it leaves a gate for the metal. Pour melted lead into the gate until it is full, then, when cool, shake it out from the sand and remove the charred paper. A file can be used to remove any rough places. The dry paper ball prevents any sputtering of the hot lead.
This idea of a hollow card or paper form buried in plain sand as a sacrificial mold for poured metal parts interested me. As the internet papercraft explosion has taught us, paper is really not a bad medium for 3D design, especially for the cost. Software like Pepakura Designer will convert any 3D digital model into a papercraft one that can be printed out, cut out, folded up, and glued or taped together to make a reasonably accurate real-world replica of the original. What if, instead of using the paper as a positive representation, one were to use it simply as a negative space–a volume, supported by dry sand, that would survive just long enough to impart its form to molten metal poured inside?
As a first experiment, I designed a paper template for the pieces of a classic put-together puzzle often called “The Four Piece Pyramid.” The challenge is to use the four identical pieces to form a symmetrical three-sided pyramid. I chose this prototype form, first, because I think the puzzle is elegant; second, because all four pieces are identical so only one template design is required; and third, because the pieces are fairly simple, geometrically, and thus so are the templates.