In 1984, inventor Charles Hull built the first rapid-prototyping machine, a massive device that turned digital blueprints into plastic models constructed layer by ultrathin layer. Since then, 3-D printers have shrunk from room-filling behemoths to tabletop boxes just larger than a typical ink jet. They have also dropped in cost from hundreds of thousands of dollars to as little as $500. Home printing has flowered as a result, with amateurs "fabbing" anything in plastic, from cellphone cases to scale models of Rodin's Walking Man. Yet such tinkering, however nifty, is simply 3-D printing's first act. Its real promise is much greater: to turn every home into a self-sustaining manufacturing and recycling center.