I ordered the BitsFromBytes RepRap kit v 2.0 last summer. I put it together just in time for the Alt Party 2008, and even got it to extrude a bit. Above is a picture of it at the Pirate Party booth, nicely illuminated by a 12V RGB LED rail. Thanks to the guys at the party who helped me to wire up the heater and test it!
However, there were multiple problems with it, and I shelved it for half a year and went to work on other projects (the major problem was that I had decided to try using ball-chain with custom drive wheels instead of the standard (but expensive) drive belt)
I took a look at it again recently, but decided to try building an own design from scratch instead of fixing it (yes I know, probably more work, but I'm a designer at heart :) ). Hopefully some useful insights come from this new project.
My goal is to create a simple design that can be easily constructed with a small amount of standard parts from a well sorted hardware store (plus electronics ordered over Internet from e.g. the rrrf store). The design should be relatively modular, with possibility to easily remove the different axis assemblies and toolheads from the box for maintenance and upgrades (the laser cut RepRap designs take a lot of time to put together, and to take apart and put back together if you want to change some part..).
I decided to put the 3D Printer in a box, as it seems that printing in a hot ambient temperature around 50-70 degrees Celsius eliminates the warping of plastics. A box also provides a sturdier frame, which could allow operating a CNC mill with the same positioning system, opening up an additional range of materials, as well as circuit board milling and drilling. The box also neatly contains the unit together with fumes and dust, making it nicer to use in a home.
I made this initial design in SketchUp, which is an excellent tool for this type of work (unfortunately I could only get version 5 to work with Wine under Ubuntu).
The box itself can be made from MDF board or Plywood with 3 cm wide wooden beams to support it. It's a bit small in this design, I'm planning to make it 50 cm wide and 60 cm deep and high in the next design iteration. I placed the stepper motors outside the box, as they are rated for at most 80 degrees celsius.
I use threaded rod to drive all three axes in this design, it's probably ok for milling, but maybe somewhat slow for 3D printing. On the positive side, the wooden box design makes it a bit easier to switch to a belt drive later if needed. Another alternative would be to use larger diameter threaded rod with some gears to speed it up.
The Z motor movement is transmitted through a bevel gear that slides along a rotating square-profile aluminum extrusion. I'm not sure how well that would work, and it would also require a custom-made part, so I will probably change it in later design iterations. This picture should illustrate it:
The stepper motors will be attached directly to the lead screws like this:
A possible improvement could be to add smaller diameter aluminum tubing to the stepper motor end to achieve a tighter fit.
It's not visible in the pictures, but I'm planning to use skateboard bearings attached to an L shaped aluminum extrusion for the linear bearings, as described on buildyourcnc.com.
I put the electronics in a drawer underneath the main box, so that they can be easily accessed, and so that heated air can be blown from the power unit and stepper controller cooling fins up through a vent to the main box, to create the preheating required for warp-free plastic extrusion.
I'm currently working on a second version of the design, which rearranges things (changing to a moving x axis and stationary bed to allow automatic tool change, and moving electronics and dust collection to the back of the machine instead of a drawer). I will post more when I get the design finalized and start building.
Edit: Added closeup of z platform.