Robot babies

The idea of a machine that could produce a copy of itself has intrigued some of the greatest minds in history. Rene Descartes heads a list of philosophers, mathematicians and physicists who have long pondered the potential of a self-replicating machine. As have writers of science fiction, who have been also quick to warn of the dangers of unleashing such a powerful technology upon the world. But for both sets of thinkers, the reality of a self-replicating machine has lain somewhere just beyond our reach.

Sitting in his office at the University of Bath, Dr Adrian Bowyer doesn't look like an evil mastermind. Bowyer is a quietly spoken, slightly podgy, twinkle-eyed 55-year-old senior lecturer at the school of mechanical engineering and inventor of the RepRap machine. Earlier this month at Cheltenham's Science Festival, Bowyer and New Zealand scientist Vik Oliver unveiled a RepRap that had the majority of its working parts "printed out" from an earlier prototype. Although the RepRap was first assembled in 2006, this was the first time a parent and child machine had appeared side by side.

Technically, the RepRap is a form of rapid prototyper, the kind used by designers and engineers to streamline everything from aircraft to hairdryers, but it's easier to think of it as a printer of three-dimensional objects. Essentially, the RepRap works like the desktop printer you might have at home, but instead of printing on paper, the RepRap makes hard copy in three dimensions out of plastic from models designed on a computer.

Even before you get into the benefits of self-replication, the RepRap is already an impressive achievement. Bowyer and an army of international helpers - all operating under an open-source license that lets them adapt and develop the blueprint collectively - have managed to scale down the cost of rapid prototypers from tens of thousands of pounds to around £250.

Bowyer describes his RepRap as "potentially an extremely powerful technology" that could "give everybody - ultimately - the ability to make virtually anything for themselves in return for being helped to reproduce". For the moment it makes crude plastic knick-knacks (sandals, coat hooks, door handles and fly-swatters), but it has the potential to develop into something that could make much more sophisticated artifacts, including the ability to lay its own circuitry.

The RepRap itself is a humble thing to see. It's small, little bigger in volume than a portable television, barely more than a frame assembled from long pieces of screw-grooved studding and a large number of plastic parts. At its heart is the all important extruder, which is poised to squeeze out a small film of molten plastic from a nozzle that is fed from a coil of white filament. It looks vaguely like a cut-price textile machine.

Bowyer sets the nozzle to work, producing a simple coathook. Line by line, layer upon layer, the RepRap begins its task. It is an agonizingly tedious process that will take it almost two hours to "print out" each small part. It will take hundreds of hours to make the parts for a "child" machine. Not that that should temper your enthusiasm. If you think back, the first digitised images took hours to process. Now, 20 years later, such things are commonplace, done in a flash on a mobile phone.

The RepRap needs to get much faster before it can even begin to realize its potential, but it is still early days for a device - even though it has been dreamt of since the dawn of the enlightenment - and Bowyer is not done yet. Soon, he plans to design a shredder for the machine, so old items created on the RepRap can be returned to granules of plastic to be reused. Think about it, he says: "You could shred your milk bottles and make a pair of sandals. What's more, when the child grows out of the shoes, you shred them, add another milk bottle, rescale the design and you have a new pair." If nothing else, the RepRap could be the ultimate recycling machine.