https://www.youtube.com/watch?v=TBOkLRoWxTE&feature=youtu.be

NOTE: The company that sold the lead screw drives for this design (Trinity Labs) has gone out of business. I have not yet found a replacement. That does not mean they are not out there somewhere. Just make sure you have them in hand before dedicating a tremendous amount of plastic to the construction of this machine. I do plan to revise the design to also use common off-the-shelf hardware, in which case it will be truly scalable on any axis.

BE SURE TO DOWNLOAD THE LATEST BUILD PDF!
TankRap #1 has been commissioned and is working properly. Notes are in the construction PDF. Yoda tested at 70% reduced size, with .5mm hot end (white ABS, yellow PLA, see photo).
The TankRap is an easy-to-assemble 3D printer, built like a tank, with accuracy in mind.

TankRap #1 survived international transit as checked luggage, and nothing broke. Testament to its ruggedness :)

This is a complete file set to build a TankRap 3d printer with lead-screw X and Y drives.
This design is easily scalable in any axis, and the frame axes are designed to mount to plywood or acrylic to both enclose the work area and prevent frame torsion.
THIS IS A WORK IN PROGRESS. I have just finished constructing it and am now testing. So far the basic first design works correctly.
I do not recommend this project for someone's first 3d printer; it takes quite a bit of plastic to print everything, and the design may not be as easy to understand as some of the other opensource repraps available.
NOTE important: I originally designed this machine around the Bulldog XL extruder, but while testing, I have found the problem I have been having with extrusion lies not with the hot ends I have been using, but with the extruder itself. Perhaps I received a lemon, but until I get a replacement that works, I cannot recommend the Bulldog. I have redesigned the X carriage to hold a Greg/Wade Accessible Extruder and whatever hot end you can attach to it (I prefer my tried-and-true Buda hot ends from Airwolf 3D)

BE SURE TO DOWNLOAD THE LATEST BUILD PDF!
Print 8x cube vertex.
Print 2x Z motor mount.
Print 2x Z idler.
Print 1x everything else (choose X carriage based on hot end type).
Uses 2x Trinity Labs lead-screws for X and Y axes. http://trinitylabs.com/products/10-start-25mm-pitch-anti-backlash-nut-fast-lead-screws
Uses 1x Greg/Wade Hinged Accessible Extruder. I prefer the older model with the closed top guide. It seems to work much better for me. http://www.thingiverse.com/thing:11892
Uses 1x Reprapdiscount Rumba control board "big box" kit.
http://www.reprapdiscount.com/kits/62-rumba-big-box-with-smart-lcd-controller-endstops-mk2b-heatbed-1-wiring-set-capable-of-24v.html
Uses 5x NEMA stepper motors. 1xX, 1xY, 2xZ. Get high torque ones (40 newtons) if you can; they make a huge difference in reliability both in terms of accuracy and not-overheating-and-crashing your controller.
I recommend an Airwolf 3D hot end. I have used this on my other printer for a long time and it works great. http://airwolf3d.com/store/products/jr-jam-resistant-3d-printer-hot-end/
If using this hot end, print the buda type x-carriage and x-linkage.
Label all your parts with a sharpie as they come off the bed, so you can keep them organized. Due to some design slop, not all clamp pieces are universally compatible with other pieces.
I have scaled up all "internal" parts to 105%, so that bearings etc will fit better. Depending on your printer you may experience slight differences in print size. Always doublecheck with some sort of calibration tester before you print, to avoid waste, and modify the STLs as necessary.
Consider building a backup X and Y axis drive coupling because (a) they are designed thin to shear off in case of an endstop failure so the machine doesn't tear itself apart and (b) you may need to drill their holes out to get them to align better.
See PDF for detailed build instructions.
My copy of Configuration.h (for Marlin) is in here for the firmware, using a homemade Greg's Wade extruder, which may vary from yours. Most important are the acceleration settings-- default Marlin settings will cause a lot of skipped steps, mostly on Y, due to backlash.