This is not the extruder you're looking for. If you're looking for the extruder referenced in Josef Prusa's i3 design, see http://www.thingiverse.com/thing:24219 A dual version of my compact extruder.The only issue I've had with the design so far is that getting the nozzles to the same height is both critical, and difficult, and requires the addition of shims between the groove mount plate, and the carriage.Unfortunately, I think that the solving the alignment issue may require changing to a "Vertical X" carriage style, so that the point where the extruder is mounted to the carriage is separated from where the hot end is mounted to the extruder.Vitamins: Extruder bodies     2 Geared stepper motor (Minbea PG35L-D48)     2 Drive wheel (MakerBot MK7 or Arcol 11x5).     2 624 bearing (4x13x5).     4 M3 x 25mm Socket head screws.     8 M3 x 35mm Socket head screws.     2 M4 x 20mm Socket head screws.     12 M3 washers.     12 M3 nuts.     2 M4 nuts.Motor sources:      http://eminebea.com/en/product/rotary/steppingmotor/pm/gearbox/pg35l-d48.shtml      http://allelectronics.com/make-a-store/item/SMT-365/STEPPER-MOTOR-WITH-GEARBOX/1.html (Out of stock.)      http://www.mpja.com/prodinfo.asp?number=18840+MS (Identical to the motor carried by All Electronics, including the vestigial gear.)Drive wheel sources:      http://store.makerbot.com/mk7-drive-gear.html      http://indiegogo.com/mini-hyena (the 11x5 version).If you purchase the motor from all electronics, you'll need a small gear puller or faucet puller to remove the vestigial gear.Vitamins: Carriage     4 igus bushings ( sdp-si.com/eStore/PartDetail.asp?Opener=Group&PartID=64165&GroupID=830 ).     3 M3 x 25mm Socket head screws.     4 M3 x 20mm Socket head screws.     6 M3 washers.     7 M3 nuts.     1 M3 locknut.Print the parts, remove the support membranes and walls (The curved ends of the belt clamps on the carriage are support walls which should be removed).Note: If you previously printed the Ron's Compact Extruder, then you can re-use it - just print xcr.stl (the mirror image of rcx.stl) and rdx_carriage.stlNote: I had to use SFACT to slice the model, because slic3r doesn't generate good toolpaths for many of the bridges, and because it leaves out the support for the belt clamp on the carriage.If you think that you need assembly instructions, refer to http://www.thingiverse.com/thing:22980 .When assembling onto your printer, it's very important that the height of the nozzles be as close as possible - one nozzle is going to be dragging over your print, while you're printing with the other one. I shimmed one of my nozzles with a couple of thin washers, and a couple of layers of kapton tape, to get it as close as possible to the height of the other nozzle. I intend to further tune it with 1200 grit sandpaper, after a bit of testing.