Rapid prototyping machines--or 3-D printers--use a small nozzle that scans back and forth across a surface, depositing tiny droplets of quick-hardening plastic. After each scan, the nozzle moves up a notch and scans again until it has built up the complete object, layer by layer. With multiple nozzles or a means of swapping supply cartridges, the machine can create objects made of many different materials. An electronic circuit, for example, can be made by combining an organic semiconductor, metallic inks and ceramic insulators.
Price tags for these machines average around $100,000, but you can now build your own for about $2,300 worth of off-the-shelf parts, thanks to the work of a Cornell University engineering professor. The prototype--called Fab@Home--is slower than commercial models and it doesn't have the same fine detail resolution, but for the price it definitely has its uses. Additionally, since the system is home-built from plans available online, you can modify the device to do whatever you want, unlike the commercial products.
You can download the plans to start building your own Fab@Home from this website. The site also includes construction hints, ideas for applications, notes on the history of 3-D printing and discussion groups. People are invited and encouraged to make improvements, and a sort of cult is slowly forming.