The RepRap revolution
by David Carpenter

DID YOU have a Sinclair ZX Spectrum or a Commodore 64 or similar in the early 1980s? Are you fortunate enough to be likely to live for another 30 years?

There is an equivalent now of those early computers in the field of RepRap, machines that can reproduce themselves or other things. With 30 years future progress in that field we can possibly look forward to an even more massive impact on daily life than the computer has had.

Machines that can reproduce themselves already exist in home workshops. The RepRap Mendel (all models are named after famous biologists as the name of the game is ‘replication and evolution’) can reproduce its own parts made from plastics by using a type of 3D printing. The hope, if not expectation, is that developments of machines like Mendel will improve beyond recognition in the way that computers have since Sir Clive Sinclair’s simple computer.

Imagine in 2041, and you need a new pair of designer specs, or a fuel injector for your quaint old vintage petrol powered car. Do you go to a retailer to buy something mass produced half a world away? No. You dial the instructions into your RepRap machine in a corner of the kitchen or utility room, and print one off!

Far fetched? Not according to Dr Mark Miodownik, one of he world’s leading materials scientists and physicist at Kings College London who you may have seen presenting the Royal Institution Christmas Lectures on the BBC over the holiday period.

Writing in The Guardian recently Dr Miodownik said: “this is not science fiction: I have a 3D printer in my lab and it works. At the moment the technology is in its early stages, but already hospitals are using it to make tailor-made implants for patients. Think what might happen if we perfect this technology. Why buy a phone, when you can design and print your own? Why buy a ring when you can express exactly how you feel by making one for your lover, or new cutlery for your mother. The possibilities are, literally, endless.”


The implications are massive.

Just think of the effect on manufacturing industry, and retailing. They won’t even be needed to supply the machines! Think of the effect on Transport and property.

Far fetched? Probably not. Model engineers are already benefiting from this 3D printing or rapid prototyping technology. Those latest castings you bought might just be from mould produced in this way. With a 3D printer and some simple CAD you can make moulds for your own complex castings. Now.

Making one of these machines will make a super exercise for many a home workshop enthusiast. The design of the RepRap Mendel is freely available. You can buy all the bits you need on Ebay and elsewhere - all produced on another Mendel. Electronics, metal rods and other parts to complete a machine are all readily available, too. There are already embryonic RepRap User Groups around the world. RUG Forums, too, are ready to provide help and advice.

At present the materials used are mostly plastics, and no doubt the smart people around the world are working on printing other materials. Also materials development generally is arguably the most important area of engineering research today. We are already seeing amazing new man-made materials coming into use.

There are other types of rapid prototyping and you can buy 3D printing machines commercially - tho’ they are beyond the pockets of all the model engineers we know.

It is the RepRap that will feature in home workshops. And it is said that the cost of building one is only around £600.

So far there have been two machines designed. First was called Darwin and the second, Mendel. A third, Huxley, is under development.

‘Copyleft’ not ‘copyright’

All of the designs produced by the project are released under a Free Software Licence,  the GNU GPL. The GPL is the first ‘copyleft’ license

for general use, which means that derived works can only be distributed under the same license terms. Under this philosophy, the GPL grants the recipients of a computer program the rights of the Free Software Definition and uses copyleft to ensure the freedoms are preserved, even when the work is changed or added to.

RepRap was founded by Dr Adrian Bowyer, senior lecturer in mechanical engineering at the University of Bath in 2005. You can find lots more about it on the internet, especially Wikipedia, the spiritual home of RepRap.

Any rapid prototyper meant to self-replicate is, by definition, a ‘RepRap’, although to date most have been based on either the Darwin or Mendel design. As an open-source project designed to encourage evolution, many variations exist, and the designer is free to make modifications and substitutions as they see fit. However, RepRap 3D printers generally consist of a thermoplastic extruder mounted on a computer-controlled  XYZ platform. The platform is built from steel rods and studding connected by printed plastic parts. All three axes are driven by stepper motors, in X and Y via a timing belt and in Z by a leadscrew.

At the heart of the RepRap is the thermoplastic extruder powered by stepper motors (sometimes geared) to drive the filament, pressing the filament between a splined or knurled shaft and a ball bearing. The build envelope for Mendel is 200 (W) x 200 (D) x 140 mm (H) or 8 (W) x 8 (D) x 5.5in. (H).


RepRaps print objects from ABS, Polyactic acid, and similar thermopolymers.

Polylactic acid has the engineering advantages of high stiffness, minimal warping, and an attractive translucent colour. It is also biodegradable and plant-derived.

Unlike in most commercial machines, RepRap users are encouraged to experiment with printing new materials and methods, and to publish their results. Methods for printing novel materials (such as ceramics) have been developed this way.

RepRap's electronics are based on the popular open-source Arduino platform, with additional boards for controlling stepper motors. The current version electronics uses an Arduino-derived Sangino motherboard, and an additional, customized Arduino board for the extruder controller. This architecture allows expansion to additional extruders, each with their own extruder controller.


RepRap has been conceived as a complete replication system rather than simply a piece of hardware. To this end the system includes (CAD) in the form of a 3D modelling system and CAM software and drivers that convert RepRap users' designs into a set of instructions to the RepRap hardware that turns them into physical objects.

Two different CAM toolchains have been developed for the RepRap.  Both are complete systems for translating 3D computer models into G-code, the machine language that commands the printer.

Virtually any CAD or 3D modeling program can be used with the RepRap, as long as it is capable of producing stereolithography files. Content creators make use of any tools they are familiar with, whether they are commercial CAD programs, such as SolidWorks, or open-source 3D modelling programs like Blender.

For that next project, then...