This is only for people who want to print really fast ;)

Its use is shown in this video:
http://www.youtube.com/watch?v=cSBqBW1w2wE

This is the filament drive mechanism end of the Bowden extruder. The same coupling could be used on the other end (the extrusion, or hot end), or a special purpose (smaller) coupling could be designed to fit your specific extruder (one that also clamps the heater insulator).

The idea of turning a nut onto the PTFE tube comes from profounddevices. I really liked it so much that I replaced my previous design to incorporate this idea.

I\'m thinking of using the nut as part of an electrical switch to get feedback of when the pressure is fully released. This way you can put reversing functionality in the firmware without needing to configure it per material.

The concept of using a Bowden cable as guide was suggested and pioneered by Ed Sells. See his post here:
blog.reprap.org/2009/04/bowden-extruder-concept.html

If you can print to high tolerances or don't mind some trial and error prints, you can use a 'push to fit' variant of this coupling:
http://www.thingiverse.com/thing:3775

1. Start printing the part.
2. Screw nuts onto the ends of the PTFE tube (see parts list). If needed, cut a little material away from at the end of the tube to make it fit.
3. If your filaments do not run through easily anymore, run a 3mm drill through the end where you have the nut.
4. If you want it to be able to stand more force, put a drop of super glue on the PTFE (above the nut) and screw the nut a bit further. Then truncate the PTFE to be flush with the nut.
5. Push it into the printed part.