My previous extruder broke so I had to make a new one, I decided to go with a new design since I was planning to hang it from the top of the printer. It became a mix from some previous extruders I used. The acrylic one from http://www.blueeaglelabs.com that came with their Kossel Clear printer and another one also here on Thingiverse from ChiggerPepi http://www.thingiverse.com/thing:245677Until now it works really well for me, but I'm still tweaking the design for easier and more all round use. If you decide to build it I would love to know how it works for you, so please let me know if you think there is stuff that could be improved. You can download the print ready slt files or the zip files if you want the parts separate. For information about what version you need, MK7 or MK8 check this: http://reprap.org/wiki/Drive-gear