Frame material

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People have built RepRap-based ... things ... out of a surprisingly wide variety of materials.

Most of the mass of the RepRap is the outer frame.

There seem to be 4 main approaches to making the frame:

  • build-up: Build the frame out of parts built-up to exactly the right shape and size.
  • modular: Build the frame out of some modular construction material, to make it easy to make a little bigger (so you can make bigger parts) or a little smaller (to improve rigidity and hopefully precision) or to otherwise experiment with different configurations. Also, once such a RepRap has been built and printed out the second generation, it can be disassembled and the parts used for other things.
  • cut: Build the frame out of some continuous material that is cut to length, and perhaps a few holes drilled in it, but not otherwise shaped.
  • shaped: Build the frame out of parts shaped to exactly the right shape and size.

The Mendel frame seems to be a pretty good compromise, combining a few "cut" parts -- the studding (threaded rod) -- and a bunch of parts built-up from thermoplastic filament using a previous generation RepRap.

The ideal material for a n+1 generation RepRap has these characteristics:

  • raw material extremely low cost
  • quick to convert raw material to parts (to reduce generation time) with nth generation RepRap
  • adequate strength-to-weight ratio so that it can hold itself up and move the tool head to a precise positions
  • ...
  • please fill in other characteristics I'm missing ...

The ideal material for a 0th generation RepStraps has these characteristics:

  • raw material easily available
  • easy for a human to shape ("easy to work") with easily available tools
  • adequate strength-to-weight ratio so that it can hold itself up and move the tool head in a precise positions
  • ...
  • please fill in other characteristics I'm missing ...


build-up construction materials

The most astonishing thing about RepRap is that it is designed out of parts that, with few exceptions, can be built-up on a RepRep.

modular construction materials

grid beam

Early version of Eiffel, showing the grid beam TriLap joints. (The beams should have through-holes repeating along the side.)

grid beam: 2"x2" square beams with a line of holes: typically used for furniture and street signs. "pre-drilled square beams". A typical piece of furniture built out of grid beam uses lots of TriLap joints.

Wooden grid beams seem easier to cut to length. Metal grid beams seem stronger and more rigid.

Does it make any sense to use a mixture of both wooden and metal grid beams bolted together?


Bitbeam is a miniaturized grid-beam system compatible with Lego Technic, using 8mm x 8mm square beams. [1] [2] [3]

extruded aluminum

  • MakerBeam; 80/20 T-slot extrusion; etc. -- T-Rep, SamBot, etc.

see Extruded Aluminum for similar aluminum materials.


"The OS (OpenStructures) project explores the possibility of a modular construction model where everyone designs for everyone on the basis of one shared geometrical grid."[5]

Based on a 4×4cm square that marks cutting lines and assembly points. Designed for disassembly, adaptation, re-assembly, and scalability. (lots of TriLap joints in the illustrations).


Main page: Contraptor
  • "Contraptor is a DIY open source construction set for experimental personal fabrication, desktop manufacturing, prototyping and bootstrapping. ... Contraptor is mechanically compatible with 1" T-slot ..., pegboard, 1" grid beam (such as commercially available perforated steel tube), and likely other things with dimensions standardized in 1" grid."

See Contraptor for more details.

other modular materials

glue gun fabber: Is this Vik Olliver's Meccano-set based RepRap prototype?

(the Free Universal Construction Kit is a set of adapters for interoperability between several of the above construction "toys").

cut-to-length construction materials

metal rods

  • 8 mm threaded steel rod (aka "threaded rod" or "allthread" or "M8 studding"): Many RepRaps and RepStraps use all-thread as a easily-adjustable frame material. Many also have at least one axis driven by a "lead screw" of 8 mm threaded road or nearly equivalent 5/16" threaded rod that acts as a worm gear, turned by a stepper motor, that pushes parts back and forth. A few use bigger sizes such as M12 and M10 threated rods in the BiBONE[7] or smaller sizes such as the 1/4 inch threaded rod used in smaller SAE Mendel machines.
  • 8 mm smooth steel rods (aka smooth rod, aka "drill rod"): Most RepRaps and RepStraps have parts that slide back and forth on 8 mm or nearly equivalent 5/16" smooth rod. A few RepStraps ( DriveTrains#rotary to linear motion conversion) spin a smooth rod with their motor rather than a threaded rod. A few use other sizes such as the 12 mm smooth rod used by HaMendel[8] and BiBone. "O1 drill rod" ? "A2 drill rod" ?

water pipe

other cut-to-length construction materials

  • low-cost softwood dimensional lumber, roughly 18x45mm and 18x70mm (close enough to "1x2" and "1x4"), bolted together -- 1X2 and WolfStrap
  • poplar planks -- Tommelise
  • extruded aluminum L rails -- Doboz
  • #extruded aluminum in other shapes

cut-to-shape construction materials

Should we distinguish between cutting flat materials into a (2D) shape (perhaps with a CNC Router) and perhaps drilling a few holes into the face and edges, vs. cutting large blocks of material into arbitrary 3D shapes?

To make future generations of self-replicating machines out of such materials seems to require a CNC Router or a Laser Cutter.

other discussions of building material

  • Wikibooks: robot building materials implies that cardboard (!) is best for quick prototypes; for functional robots, "wood is probably the best material to start with."; where wood isn't quite durable enough, aluminum is the best metal -- better than steel for most robots.
    • Is "edgeboard"[14] the same as corrugated cardboard? It's apparently strong enough to hold up full-sized humans; is it strong enough to hold up an extruder nozzle?
    • Is it possible to build a FlatPack RepStrap mostly out of "Laminated Laser-cut Cardboard"[15]?
      • Izhar Gafni has made a type of bicycle with a composite frame (cardboard & epoxy?/some polyester?) ("Cardboard Bicycle"). It is apparently waterproof and strong enough to hold up full-sized humans. It is definitely worth an investigation, if nothing else for the other end of the M8 threaded rod there.. are on several levels; Epoxy Granite.

  • User:Mrkim mentions various "Classes of machines",[16][17] including entire classes of machines that the above seems to neglect.