It's clear from the RepG source code and firmwares on git that Makerbot is just about to release a MK6 extruder, which will be stepper-driven on the 4th axis of the Thing-O-Matic. You can stay ahead of the curve by getting in now! Driving your stepper from the axis gives you control as fine as you'd possibly like. In addition, it's a great way to get around the problems some people (me!) have had with the Thing-O-Matic extruder controller's motor port; it's not used in this build (although I /think/ the firmware wants a cooling fan for the stepper motor on that port now, I'm still investigating).The video of me testing the extruder after hooking it all up is here: http://www.youtube.com/watch?v=fegRf_M_GBk Here's an earlier video from my bench-test before putting it all back together: http://www.youtube.com/watch?v=M2OBWO2ooWEPLEASE NOTE: If you want to build this and use it, YOU MUST USE THE LATEST REPG AND FIRMWARE! This is BLEEDING EDGE development; in fact I can guarantee you the files below are already technically out of date. Also I can't accept any responsibility for the firmware files below; if they ruin your machine, don't come crying to me. If you want to do it right, get the firmware from the git repo and compile it yourself. It's not hard.!Print 1 of these: http://www.thingiverse.com/thing:5164 Or the newer design here: http://www.thingiverse.com/thing:5795If you want yours to look just like mine, you'll also need one of these: http://www.thingiverse.com/thing:5169However, that last part is just a hole-compatible MK5 top peice, so if you want to hook all this up to your existing plastic pusher, you can do that instead.I can try to provide better instructions, but I think you'll get the idea from the pictures. You need:1 stepper motor (Mine is from a cupcake) 1 stepper controller (Mine is the old 2.3 version, again from a cupcake)1 606 bearing IN ADDITION TO the 1 already in your MK5 plastic pusher. 1 #6 bolt, 40mm. I used 50 here, but it's about 1cm too long. No worries. A couple washers and nuts. The nifty plastic-pushing gear from your existing MK5. Miscellaneous M3 hardware (probably leftover from your machine build).Now, if you have a MakerBot Stepper Controller 3.3 you just wire it up in the obvious fashion and hook it up to the A AXIS.If you have a MakerBot Stepper Controller 2.3 (the CupCake one) like I do, you need to make a special cable to attach it to the A Axis port. The 2.3 controllers use a 10-pin connector, but the motherboard has a 6-pin connector. Just use the first five (not six!) pins and connect them straight across. See the attached photos. In addition, if you have the CupCake 2.3 controller, you are going to need to change your RepG profile; the profiles I mention in the next paragraph are set to 1600 steps, but your CupCake controller needs you to set it to 200 in machines/makerbot.xml.Either way, you're going to need to make a longer cable for the stepper, I'm sure. I did it using a (too-long!) piece of shielded 4-wire twisted pair cable, but you can use whatever is handy. I also made 'quick connects' for the cable using some DB9 connectors, since they were handy.After hooking that all up, and installing the firmware, you can start up the latest RepG (which you got from the git repo, right!?) and choose File->Preferences->Show Experimental Machine Profiles. Then go to the Machine Menu->Driver->Thingomatic w/HBP and Stepstruder MK6, or w/ABP as appropriate. Now YOU are part of THE FUTURE.