I keep trying to persuade anyone who will listen that CNC foam cutters are dramatically underrated machines. People look at them and say, “That’s cool and all, but I don’t want styrofoam parts.” To which I reply, “If you have a styrofoam part, you can turn it into cast aluminum with an unbelievably simple garage process.” What’s more, styrofoam is ubiquitous, cheap, and so easy to cut that the Cartesian robot can be extremely lightweight and inexpensive, as for instance, this one submitted by reader Raul Aguaviva, which is hacked together from a coat hanger and junked scanner parts. Combine one of these with a Gingery-style charcoal foundry and you could conceivably produce a homebrew rapid prototyping system, capable of “printing” aluminum parts, for less than $50.