Rubberband Direct Extruder MK7 Hobbed Bolt

Requires:
1 NEMA 17 Stepper Motor
1 Hobbed Bolt (Preferably a Makerbot Stepstruder Mk7 or Mk8)
2 M3X20 screws
2 M3X25 screws
1 608 bearing
Rubberbands

The idea for this extruder drive is for a simplistic design, but one that works and doesn't use too many parts you have to find from elsewhere. Most direct extruder drives require extra screws, washers, springs and nuts but this one only requires the use of rubberbands. Do not add too many rubberbands, as this will cause your motor to start skipping. This effect also occurs if you are using a spring-based direct extruder drive and your spring tension is too high.

I use Blue coloured round Theraband. I basically cut a few 2-3mm thick strips. you may use other colours like black instead, and use fewer rubberbands. I use up to 3 blue theraband strips like this and this works just fine, printing at speeds up to 100mm/min. haven't tried faster though.

The file 'bottom' is made specifically as a replacement for Reprap Mendel Prusa. there is sufficient space between the mounting plate and the 'bottom' mount for most nozzles. if you'd like you can design and print your own nozzle mount as appropriate.

Update:
I have shifted the Portabee files to another page to make things less confusing.
they may be found here
http://www.thingiverse.com/thing:244084