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I keep having a recurring problem with my ender 3 pro. The bowden tube keeps popping off here (pictured)

enter image description here

I've read elsewhere online where people are having a similar problem, i.e. the ptfe tube is actually popping out, but I don't know if thats the case here. It's staying attached to the metal coupler, but that metal coupler is unscrewing during the course of the print and falling out. Any tips to fix it? New one? Some sort of loc-tite to get it to not unscrew? Any ideas?

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The fitting can be defective and no longer hold upon the PTFE tube anymore. In that case, you need to cut off a short piece of the tube and most likely replace the fitting.

If the metal coupler unscrews you can fix that by properly screwing it tight. If it does not stay put after applying some torque upon it, then the screw thread is broken, and the whole extruder gearing-setup needs to be replaced. An aluminium swap part costs about 10 to 15 €.

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  • $\begingroup$ I’ll agree that the threads must be damaged. On my Ender 3 Pro, that connector is only tightened finger tight and it never unscrews by itself. $\endgroup$
    – DoxyLover
    Jan 2 at 5:45
  • $\begingroup$ @DoxyLover I unscrew that end regularily because it makes loading easier :3 $\endgroup$
    – Trish
    Jan 3 at 19:46
  • $\begingroup$ @Trish If you put a bevel on the inside of the PTFE tube, that can make loading easier. $\endgroup$ Jan 4 at 12:59
  • $\begingroup$ @AndrewMorton no, it's a problem with the fitting bevel being too small, a tiny lip that the filament hits on loading on the fitting. $\endgroup$
    – Trish
    Jan 4 at 13:12
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    $\begingroup$ It was simply unscrewing. The threads didn't look damaged so I simply tightened a bit more (with a wrench this time instead of just my fingers) and added a bit of loctite (the removable kind) and its held for two prints so far. $\endgroup$ Jan 4 at 21:19
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If the fitting is remaining attached to the PTFE tubing, that would indicate that the threaded end of the fitting is pulling out of the drive assembly. This implies that the internal threads of the drive assembly have stripped out. This is not unusual for a plastic drive assembly.

The best solution is to replace the drive assembly. I believe I paid about US$12 for the last one I purchased and it was aluminum, not plastic. A quick search for "Ender 3 drive mechanism" returned a number of choices. One of them from Amazon (14.98) is anodized aluminum and purports to be improved over the original.

ender 3 compatible drive assembly

A less than ideal solution would involve drilling out the stripped threads and installing an insert (sometimes called a Heli-coil™) but that could be as expensive as a replacement mechanism.

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