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UM2 - Removing bowden tube very often -> wear

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more often that not I have to remove the bowden tube (head end) because some filament strands get caught inside the tube. This is a problem because the bowden clamp will play nice only so many times and then the tiny teeth will loose their grip.

Another issue occurs when the filament strand snaps off and stays on the teflon coupler.


If you look closely, you'll see the red filament strand. If I were to insert the bowden tube now, I would wedge in the strand between tube and teflon coupler. This would block the path for the new filament and/or will slowly dispense some red filament and ruin prints visually.

Not to mention that it is quite annoying to have filament strands that end in a blob of plastic, inside the extruder. I bought a crochet hook in order to fish for loose filament inside the extruder, but it ain't nice anyway.

I suggest the filament changing procedure should be adjusted (less heat, pulling faster at the beginning and then slowing down - not sure). This will surely tone down a few support requests for broken bowden tube clamps in the future (and make filament swapping easier).

What do you think?


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Yup, I've been warning people about this for a long time, "good" to have someone agree with me finally hehe (although I've seen gr5 mention it a bit lately as well).

This is one of the reasons I designed my alternative feeder, to make swapping filaments easier. Being able to give the filament a good powerful tug when it has cooled down a bit means you get all of the old filament out in one go and when you put a new filament in you don't have to sit there and extrude for 3 minutes to make white PLA actually white.

However, I can't say that remaining strands in the bowden was ever a problem for me before. I always just loaded the new filament and those tiny strands would get pushed into a small "hair ball" and then get pushed down into the nozzle with the new PLA.

I noticed when doing the filament change procedure with the newest firmware (instead of manually like I usually do these days) that it pulled out quite slow at first and then sped up after a few cm were pulled out. I don't know what the logic is behind it. Pull out, let cool, speed up to break the strand that forms?


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I agree. I recently stopped changing filament the "normal" way. Robert kept mentioning that he could push and pull filament through the UM2 feeder if the stepper was off and he's right - it doesn't really take much force at all - less than 1kg I think.

So my new procedure is to heat head to 90C to 120C region and when temp is around there I just pull it out! :)

Then I heat to 180C (or don't even bother with that) or so and push the new filament in. It's much faster also!

Sometimes I go to move filament (once the new filament is in) and spin the knob until the color changes or at least until it is primed.

Now I like this so much - I get to feel the resistance of the bowden with my hands. It's always good to have a feel for what might be causing "extruder skips" or other issues.

It's surprising but pretty much every time I go to do something like this the feeder motor is off. This is very convenient. I haven't had to cut power (to get the feeder stepper into an off state) yet.


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I dunno, the filament changing procedure sounds tedious. And my problem is that the space behind my UM2 is very limited. I can only access it from the front and need to bend over the table because I can't get behind the printer. Already got a manly scar on my thumb when I tried to pull filament out of the extruder and rammed my thumb into the (sharp) side of the case...

So right now I am relying on the standard filament changing procedure and hope for the best.


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