RepRap .34mm Nozzle with 3mm ID Feed Path and 1.75mm ABS

As the title suggests, I was (unknowingly) attempting to run 1.75mm filament through a 3mm  inside diameter PTFE rod to my hotend. I ordered all of the hardware for my kit from the same location and everything was specified in 1.75mm dimensions for the filament – I made the mistake of assuming that I received what I had ordered.

The PTFE rod, when I did measure it, turns out to be 3mm. Due to the pressure required to force filament through a .34mm nozzle (most use 5mm or 4mm) the amount of play in the filament channel causes the downward force of the extruder to push the filament sideways. In the case of PLA this causes a clog right above the brass channel, with ABS something stranger happens when there is cooling on the cold end.

I had to add cooling to the extruder because it was warping under the heat and pressure of trying to run this setup. The cooling seems to have caused it’s own issues by being too effective.

The end result is the filament (which twists coming off of the spool and going into the extruder) melts in the hot end, but cannot produce enough force to extrude through the nozzle effectively. As it softens in the brass tubing it kinks around and produces something like this:

As you can see, I tried it many times at various temperatures and settings to prove this was indeed what was happening. I have contacted the supplier of the PTFE tube and let them know their error and provided this photo of the problem with the “1.75mm” rod.