The RepRap Project

The RepRap project is an initiative to develop a 3D printer that can print most of its own components. RepRap (short for replicating rapid prototyper) uses a variant of fused deposition modeling, an additive manufacturing technique. The project calls it Fused Filament Fabrication (FFF) to avoid trademark issues around the “fused deposition modeling” term.

As an open design, all of the designs produced by the project are released under a free software license, the GNU General Public License.

To date, the RepRap project has released four 3D printing machines: “Darwin”, released in March 2007, “Mendel”, released in October 2009, “Prusa Mendel” and “Huxley” released in 2010. Developers have named each after famous evolutionary biologists, as “the point of RepRap is replication and evolution”.

Due to the self-replicating ability of the machine, authors envision the possibility to cheaply distribute RepRap units to people and communities, enabling them to create (or download from the Internet) complex products without the need for expensive industrial infrastructure (distributed manufacturing)[1] including scientific equipment.[2] They intend for the RepRap to demonstrate evolution in this process as well as for it to increase in number exponentially.


RepRap was founded in 2005 by Dr Adrian Bowyer, a Senior Lecturer in mechanical engineering at the University of Bath in the United Kingdom.

Reprap family tree visualising the evolution of the RepRap and some other 3d printers over time

23 March 2005
The RepRap blog is started.
Summer 2005
Funding for initial development at the University of Bath is obtained from the UK’s Engineering and Physical Sciences Research Council
13 September 2006
The RepRap 0.2 prototype successfully prints the first part of itself, which is subsequently used to replace an identical part originally created by a commercial 3D printer.
9 February 2008
RepRap 1.0 “Darwin” successfully makes at least one instance of over half its total rapid-prototyped parts.
14 April 2008
Possibly the first end-user item is made by a RepRap: a clamp to hold an iPod securely to the dashboard of a Ford Fiesta.
29 May 2008
Within a few minutes of being assembled, the first completed “child” machine makes the first part for a “grandchild” at the University of Bath, UK.
23 September 2008
It is reported that at least 100 copies have been produced in various countries. The exact number of RepRaps in circulation at that time is unknown.[3]
30 November 2008
First documented “in the wild” replication occurs. Replication is completed by Wade Bortz, the first user outside of the developers’ team to produce a complete set for another person.
20 April 2009
Announcement of first electronic circuit boards produced automatically with a RepRap, using an automated control system and a swappable head system capable of printing both plastic and conductive solder. Part is later integrated into the RepRap that made it.
2 October 2009
The second generation design, called “Mendel”, prints its first part. The Mendel’s shape resembles a triangular prism rather than a cube.
13 October 2009
RepRap 2.0 “Mendel” is completed.
27 January 2010
The Foresight Institute announces the “Kartik M. Gada Humanitarian Innovation Prize” for the design and construction of an improved RepRap. There are two prizes, one of US$20,000, and another of $80,000. The administration of the prize is later transferred toHumanity+.[4]
31 August 2010
The third generation design, “Huxley”, is officially named. Development is based on a miniaturized version of the Mendel hardware with 30% of the original print volume.
First half 2012
RepRap and RepStrap building and usage are widespread within the tech, gadget, and engineering communities. RepRaps or commercial derivatives have been featured in many mainstream media sources, and are on the permanent watch lists of such tech media as Wired and some influential engineering-professionals’ news media.[5]
Late summer/fall 2012
There has been much focus on smaller startup companies selling derivatives, kits, and assembled systems, and R & D results into new related processes for 3D Printing at orders-of-magnitude-lower prices than current industrial offers. In terms of RepRap research, the most notable result is perhaps the first successful Delta design, Rostock, which is maturing slowly and has an initial working solution for experimentation by self-sourcing builders of some experience. While the Rostock is still in an experimental stage with major revisions almost monthly, it is also near the state of the art, and a radically different design. Latest iterations use OpenBeams, wires (typically Dyneema or Spectra fishing lines) instead of belts, and so forth, which also represents some of the latest trends in RepRaps.


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-controlledCartesian XYZ platform. The platform is built from steel rods and studding connected by printed plastic parts. All three axes are driven bystepper 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. Early extruders for the RepRap used a geared DC motor driving a screw pressed tightly against plastic filament feedstock, forcing it past a heated melting chamber and through a narrow extrusion nozzle. However, due to their large inertia, DC motors cannot quickly start or stop, and are therefore difficult to control with precision. Therefore, more recent extruders use stepper motors (sometimes geared) to drive the filament, pinching the filament between a splined or knurled shaft and a ball bearing.

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 Sanguino motherboard, and an additional, customized Arduino board for the extruder controller. This architecture allows expansion to additional extruders, each with their own extruder controller.

Major revisions

The first publicly released RepRap, Darwin, has an XY gantry mounted above a moving Z-axis print bed. Darwin’s Z axis is constrained by a leadscrew at each corner, all linked together by timing belts to turn in unison. Electronics are mounted on the steel supports of its cuboid exterior, and on a second platform at the base. In an effort to minimize the number of non-printed components (or “vitamins”), Darwin uses printed sliding contact bearings on all of its axes.

Mendel replaced Darwin’s sliding bearings with ball bearings, using an exactly constrained design that minimizes friction and tolerates misalignment. It also rearranged the axes, so that the bed slides in the horizontal Y direction, while the extruder moves up and down and in the X direction. This makes Mendel less top-heavy and more compact than Darwin, while also removing the overconstraint of Darwin’s four Z axis leadscrews. The build envelope for Mendel is 200 mm (W) × 200 mm (D) × 140 mm (H) or 8″ (W) × 8″ (D) × 5.5″ (H).


RepRap has been conceived as a complete replication system rather than simply a piece of hardware. To this end the system includescomputer-aided design (CAD) in the form of a 3D modeling system and computer-aided manufacturing (CAM) software and drivers that convert RepRap users’ designs into a set of instructions to the RepRap hardware that turns them into physical objects.

Initially two different CAM toolchains have been developed for the RepRap. The first, simply titled “RepRap Host”, was written in Java by lead RepRap developer Adrian Bowyer. The second, “Skeinforge”, was written independently by Enrique Perez. Both are complete systems for translating 3D computer models into G-code, the machine language that commands the printer.

Later, other programs like slic3r, pronterface, Curarepetier host were created. The closed source KISSlicer also seems popular.

Virtually any CAD or 3D modeling program can be used with the RepRap, as long as it is capable of producing STL files.(slic3r also supports .obj and .amf 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 modeling programs like Blender or OpenSCAD.

Replication materials

RepRaps print objects from ABSPolylactic acidNylon(possibly not all extruders capable), HDPE 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. In addition, several RecycleBots have been designed and fabricated to convert waste plastic, such as shampoo containers and milk jugs, into inexpensive RepRap filament.[6]

The RepRap project has not yet identified a suitable support material to complement its printing process.

Printing electronics is a major goal of the RepRap project so that it can print its own circuit boards. Several methods have been proposed:

  • Wood’s metal or Field’s metal: low-melting point metal alloys to incorporate electrical circuits into the part as it is being formed.
  • Silver/carbon-filled polymers: commonly used for repairs to circuit boards and are being contemplated for use for electrically conductive traces.[7]
  • Direct extrusion of solder
  • Conductive wires: can be laid into a part from a spool during the printing process


Other 3D printer designs (such as the commercial Makerbot) and parts constructed by other means (such as Meccano) may be used to “bootstrap” the RepRap process by building RepRap parts. Many such machines are based around RepRap designs and use RepRap electronics. These are generally known by the name RepStrap (for “bootstrap RepRap”) by the RepRap community. A RepStrap is any open-hardware rapid-prototyping machine that makes RepRap parts and is itself made by fabrication processes which aren’t under the RepRap umbrella yet. Some RepStrap designs are similar to Darwin or Mendel, but have been modified to be made from laser cut sheets or milled parts. Others, such as the Makerbot, share some design elements with the RepRap (especially electronics) but with a completely reconfigured mechanical structure.

Although the aim of the project is for RepRap to be able to autonomously construct many of its own mechanical components in the near future using fairly low-level resources, several components such as sensors, stepper motors, or microcontrollers are currently non-replicable using the RepRap’s 3D printing technology and therefore have to be produced independently of the RepRap self-replicating process. The goal is to asymptotically approach 100% replication over a series of evolutionary generations. As one example, from the onset of the project, the RepRap team has explored a variety of approaches to integrating electrically-conductive media into the product. The future success of this initiative should open the door to the inclusion of connective wiringprinted circuit boards, and possibly even motors in RepRapped products. Variations in the nature of the extruded, electrically-conductive media could produce electrical components with different functions from pure conductive traces, not unlike what was done in the sprayed-circuit process of the 1940s named Electronic Circuit Making Equipment (ECME), described in the article on its designer, John SargrovePrinted electronics is a related approach. Another non-replicable component is the threaded rods for the linear motions. A current research area is in using replicated Sarrus linkages to replace them.[8]

Project members

The “Core team” of the project[9] includes:

  • Sebastien Bailard, Ontario
  • Dr. Adrian Bowyer, Senior Lecturer, Mechanical Engineering Department, University of Bath
  • Michael S. Hart, creator of Project Gutenberg, Illinois
  • Dr. Forrest Higgs, Brosis Innovations, Inc., California
  • Rhys Jones, postgraduate, Mechanical Engineering Department, University of Bath
  • James Low, undergraduate, Mechanical Engineering Department, University of Bath
  • Simon McAuliffe, New Zealand
  • Vik Olliver, Diamond Age Solutions, Ltd., New Zealand
  • Ed Sells, postgraduate, Mechanical Engineering Department, University of Bath
  • Zach Smith, United States
  • Erik de Bruijn, The Netherlands
  • Josef Průša, The Czech Republic

Project sponsors include:[10]


The stated goal of the RepRap project is to produce a pure self-replicating device not for its own sake, but rather to put in the hands of individuals anywhere on the planet, for a minimal outlay of capital, a desktop manufacturing system that would enable the individual to manufacture many of the artifacts used in everyday life. From a theoretical viewpoint, the project is attempting to prove the hypothesis that “Rapid prototyping and direct writing technologies are sufficiently versatile to allow them to be used to make a von Neumann Universal Constructor“.[11]

The self-replicating nature of RepRap could also facilitate its viral dissemination and may well facilitate a major paradigm shift in the design and manufacture of consumer productsfrom one of factory production of patented products to one of personal production of un-patented products with open specifications. Opening up product design and manufacturing capabilities to the individual should greatly reduce the cycle time for improvements to products and support a far larger diversity of niche products than the factory production run size can support.

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