Most of the metalwork that I do at present is in silver
Burr puzzles are apparently simple things, normally made of wood. Following some extensive modeling, people have designed a series of these puzzles that are very difficult and there are various classes of difficulty for them. Here are a couple of bits that I milled out of aluminium square section tube. Because the tube is hollow, it is possible to cheat with these particular designed and twist pieces in place. For details about Burr Puzzles designs, analysis and solutions, see this excellent IBM site.