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Bowden tube comes loose in mid-print

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I've been doing some 10 hour prints on a UM2, using a .8mm nozzle and printing layers of .2mm. Jobs have failed twice with the bowden tube becoming disconnected from the print head, with the result that filament has just been pushed through into empty space. I've been printing for 3 years and this is the first time this has ever happened to me. The tube was fed into the print core in the normal way, with the little blue clip holding the white bit up and seeming locking the tube in place. Before the second print, I specifically checked the tube and I confirmed that it could not be pulled out. I'm also pretty sure that it had been pushed right down. Certainly, there had been no problems when I reloaded filament at the stat of the job. I was checking these jobs about every four hours, so I did not pick up any advance notice that this was going to happen.


So what on earth might have caused the bowden tube to pull out of the print core in the middle of printing something which should just have involved continuous printing? Could it be something to do with the volume of filament that I was printing - wide nozzle, thick layers? I was using one of the 3D infill patterns, so might they be posing issues? It's a machine which I've had for three years, and I can't remember if I've ever changed the Bowden tube so, might the age of the tube be an issue?

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Every time you remove the bowden it tends to get worse.  But don't let that discourage you from removing it.  The fix is easy.  Inside the collet (that ring that holds the bowden in place) are 4 tiny metal blades.  They can scrape the outer surface of the bowden.  It's not obvious, the bowden may look fine.  Anyway...


Remove the bowden and look in the collet to make sure the 4 blades are still there (one may have broken off) and make sure they look the same.  Assuming the collet is fine (it usually is) cut off about 4mm from the end of the bowden.  This way when you insert the bowden back in the blades will get a grip on a fresh location of the bowden.  That's it.  Fixed.

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