Clearing a plugged nozzle

[gcan...@mtu.edu]

One of the teams has reported that their nozzle has become plugged. This typically occurs either as a result of bad filament (filament having some contamination) or a small piece of PTFE comes off the Bowden sheath. Clearing the plug can be problematic - I've thought I had successfully cleared blockage only to find that I had simply pushed up up the hot end so it plugged again shortly after printing.

Which is a good point - pushing something like a wire up the nozzle when it's hot doesn't work. The blockage must be removed from the filament side.

What we've found to work best is to heat the hot end to operating temperature, push a little filament through it, and then let it cool and carefully and slowly pull the filament back out of the hot end when partially molten. I've found 75-85 degrees C to be a good temperature to start pulling the filament back out. The goal is to remove everything in the hot end - too warm and the filament breaks off, too cold and the filament sticks to the hot end. If the temperature is right, the filament feels a bit elastic as you pull on it.

The above process may work better with the Bowden sheath removed from the x-carriage, which requires disassembling the extruder drive after pulling all the filament out.

[Michael Attan]

We had an issue with a new hot head not taking filament. Here's how I ended up diagnosing/fixing it:

Tried removing the hot end from the batmobile, heating it to ~210 C and manually pushing filament...no go. Either the inner sheath was plugging the hole, or the end was plugged.

With the end still heated, I took an insulin syringe and CAREFULLY inserted it into the tip (from the bottom)...lo and behold, it cleared.

Not sure what the gauge was, but the insulin needle had a 0.33 mm end, and it fit perfectly. (My pipette tip cleaning wire was too big)