o 1 Dremel bit #196 (high speed cutter)
o 1 m3x25 screws
o 6 m3x10 screws (If you have a 6mm one, it will simplify things)
o ~6 m3 washers
o 4 m3 nuts
o 1 20mm 8mm threaded rod
o 1 608 bearing
o 2 r2zz bearings
o 4 m4 nuts
o 2 m4x50 screws
o 1 nema 17 stepper motor
Please note, the STLs are all configured for 1.75mm filament. If you want to use this for 3mm filament, please download the source and export your own STLs.
Print the four parts, main block, idler, large gear and small gear. I put the main block and idler in a combined STL, but I was using a printer with a 10x10cm print area, so it didn't fit. I included the idler and main block as separate STLs as well. After printing, make sure your holes are big enough, otherwise drill them. Some holes are covered by filament and must be drilled. Also snap off the hinge support.
While it's printing, you can work on flattening the end of the dremel shank. Don't bother trying to use a file, it won't make much of a dent on the hardened steel. Instead you'll need something to grind it with. Something with a moving sandpaper for instance. (See attached picture) Oh, and if your motor shaft is not flattened already, you'll need to do this for the motor shaft too. (See reprap wiki for details on this.)
Once the preparations are complete, you'll need to mount the small gear on the motor. If you're lucky, and have a long motor shaft, you can invert the gear before you print it and mount it with the set screw away from the motor body. For me, this did not work, and a standard m3 10mm screw is too long. (Hits the motor mount) However, a few minutes with a file will easy convert a 10mm screw into a 6mm screw. You can also file the head down a bit to make sure it doesn't hit anything. Now drop an m3 nut into the slot (requires some force) and then fasten the small gear to the motor shaft.
Drop an m4 nut into the slot in the base under the motor mount and tape it in place. You can do this later, but it's just easier to do it now. Put the motor in place with 3 x 10mm m3 screws and washers, but don't tighten yet.
The large gear has two nut traps, this is because we need a lot of force to hold the dremel shaft, and using a single set screw causes the gear to wobble. Push m3 nuts into the nut traps of the large gear and put set screws in.
Take the two r2zz bearings, push one in from each side of the main block. Put a m3 washer on the dremel shank and push it through until it starts to poke out the back. Put as many m3 washers as you need to align the gears up on the dremel shaft (2 for me). Then put the large gear in place and push the dremel bit in all the way. Now tighten the set screws of the large gear, make sure one of them hits the flat part of the dremel shaft.
Now adjust the motor and tighten. Make sure gears are working smoothly.
Now for the idler.. Put an 608 bearing on a 20mm piece of threaded rod (8mm) and snap it into place in the idler. This might take some force. Then hold an m3 nut in place inside the idler hinge while you insert an m3x25 screw from the outside. After it is screwed half-way into the nut, put the idler in place and screw the screw in all the way.
Drop m4 nuts in the nut traps on top of the block, put springs, rubber grommets or whatever you have handy on the m4x50 screws and screw them into the screws, don't bother tighten until you have some filament in there. Springs are nice, but rubberized washers works too, as you can see from my picture.
In your firmware, set the steps per mm to:
steps microsteps 47/9 / (sin(pi/10) 10 7/32 * 25.4)
With 200 steps and 32 microsteps, this comes out to 1939.