Roboticist Hod Lipson wants you to stop shopping and use his portable 3-D printer to make your own stuff. As a child, Hod Lipson lost Lego pieces constantly. Now the 39-year-old director of Cornell University’s Computational Synthesis Lab can build replacement parts on the spot. Completed last year, Lipson’s fabrication machine, called a “fabber,” can print thousands of three-dimensional objects, everything from toy parts to artificial muscles, using dozens of materials, including PlayDoh, peanut butter and silicone, by following simple directions sent to it by a PC. About the size of a microwave, the fabber costs $2,300 to assemble—roughly one tenth the cost of commercial 3-D printers. Lipson and his graduate student Evan Malone recently launched a Web site called Fab@Home (fabathome.org) to teach people how to build their own fabbers and encourage them to share their blueprints online.