More than 50 years ago, computer pioneer John von Neumann conceived of a self-reproducing machine. It would mine its own ore, smelt it into metal ingots, machine the ingots into parts, and assemble the parts into a copy of itself. During the 1980s, nanotechnology evangelists worked out the same idea on a much smaller scale, prompting critics to envision a horror scenario in which molecule-size bots reduce the entire world to a featureless mass dubbed ”gray goo.”
Today there’s RepRap. Unlike gray goo or von Neumann’s idealized machines, RepRap (short for ”replicating rapid-prototyper”) doesn’t harvest its own materials. But also unlike them, it’s entirely real. For about US $725 in parts, this self-reproducing machine, spawned by a global band of engineers and hobbyists, will squirt out complex three-dimensional patterns of molten plastic filaments that will solidify into most, if not all, of the mechanical parts for another RepRap (see sidebar, ”Self-Reproduction Is Hard; Selfâ¿¿Assembly Is Harder”).
RepRap consists of a roughly cubical half-meter frame enclosing its fabrication volume, along with motors, drive electronics, and one or more ”write heads” that extrude plastic (or some other material) into the desired shapes.
RepRap gets its instructions from your PC, via a USB connection. Software on the PC, written in Java, takes design files produced by 3-D drawing programs and turns them into instructions for the RepRap. The software converts solid-object models into a series of movements with the extruder on or off, and with either sparse or solid interior filling, depending on a part’s structural requirements.