A self-replicating 3D printer that spawns new, improved versions of itself is in development at the University of Bath in the UK.

The "self replicating rapid prototyper" or RepRap could vastly reduce the cost of 3D printers, paving the way for a future where broken objects and spare parts are simply "re-printed" at home. New and unique objects could also be created.

3D printing - also known as "rapid prototyping" - transforms a blueprint on a computer into a real object by building up a succession of layers. The material is bonded by either fusing it with a laser or by using alternating layers of glue. When it first emerged in the mid-1990s, futurists predicted that there would be a 3D printer in every home.

But they currently cost $25,000 (£13,000) and so have not caught on as a household item, says Terry Wohlers, an analyst at Wohlers Associates, a rapid prototyping consulting firm in Fort Collins, Colorado, US. Instead, they are used by industry to develop parts for devices such as aircraft engines, spaceships and hearing aids.

Plummeting prices

Now Adrian Bowyer hopes to change that by making the first 3D printer capable of fabricating copies of itself, as well as a wealth of everyday objects. He reasons that prices would plummet to around $500 if every machine was capable of building hundreds more at no cost beyond that of the raw materials.

Better still, the machines could evolve to be more efficient and develop new capabilities, says Bowyer. Once he has the software to guide the self-replicating process, he plans to make it freely available online, allowing users to contribute improvements, just like the open-source Linux computer operating system, he says.

Bowyer dreamt up the idea of the RepRap in February 2004. But now he has he figured out how to print conducting materials in three dimensions without using a laser, a key step if the machine is ever to make copies of itself.

"We are very constrained in our access to materials," he explains. They must be sturdy enough to make up the body of the machine and yet simple enough to be fabricated entirely by the machine. "We have to avoid any design needing lasers and high precision measuring systems," he explains.

Tepid metal

3D printers normally build circuits by fusing together a powdered metal with a laser. But Bowyer plans instead on using a low-melting point metal alloy of bismuth, lead, tin and cadmium that can be squirted from a heated syringe to form circuits.

Bowyer has already produced an electronic circuit by squirting the alloy inside a plastic autonomous robot, which itself was created using a commercial 3D printer. Because the heated syringe he used is very similar to the nozzle that deposits plastic layers in the printer, he envisions squirting both plastic and metal from the same nozzle in future self-replicating machines.

The machine need not be capable of assembling itself, he says, only producing all the necessary parts, with the exception of the microprocessors and the lubricating grease. These could later be added and the various parts clipped together, Bowyer says. "People are quite capable of assembling things if they want to," he adds. "I am not interested in self-assembly, just self-copying."

Whether such a machine would work has experts sharply divided. "I think Dr Bowyer's idea is very plausible," says Matt Moses, a consultant who has built a small self-replicating robot and advises NASA on research into self-replicating machines for space.

But Wohlers disagrees: "[Bowyer] is referring to something that does not exist and has not been demonstrated. Will it develop in the future? Unlikely."

He adds that even if all its components could be replicated by the machine, the concept does not make economic sense. "Many of the components could be produced much faster and cheaper by other machines," he says.