Posted by: @protoncek-2

I ended up buying MMU3, and it's even more of the mess there:  start with "ugly" and place consuming/wasting reel placement, odd filament buffer which is PITA to handle with ... so i ended up with "Rewindr" system. It rolls back very nicely using gravity. I've had to remodel one gear a bit, but otherwise it works pretty well. I also made "coreboxx" case to sit at the top of core one, so i ended up with a printer which should be a factory default for MMU3 in the first place.

I've only been using Prusa printers a couple of years but it seems (to me at least) that they take the reprap philosophy to heart. Do the basic engineering and then let the customers fix it with mods. 

just put the filament back on the spool and don't worry about it.

Yeah... i guess you're right... at least until all it does is tangle at the end of print. If things will start to go wrong during print then it'll be worrying. And, correct, MK4 doesn't have long tube, so air between spool and intake acts like a buffer.

That's why there is a filament buffer and all kinds of auto rewind spool designs for use with the MMU3. 

So if i wanted to be "picky" i could make one of that mmu3 buffers... on the other side, MMU3 just came out for core one, and it's tempting...

Posted by: @protoncek-2

I'm thinking that it can be because spool "hangs" on holder it doesn't roll evenly - instead it "leans" forward and when tension is over limit it "jumps" (unrolls) and it does it too much. I think that's why some guys created a holder with teflone tubes for smoother rolling... 

iftibashir: what holder do you use?

Having the filament retracted from the nozzle means there's no oozing when heating up and I can swap the nozzle before a print without having to unload the filament and waiting for the hotend to cool down again. Prusa implemented it for multiple reasons, with the only downside being the tangling on full rolls. 

Just take off the little string on the nozzle after each print and check the spool. 

 It never happened on MK4S... not once

Did you feed your filament into your printhead through a bowden tube? If not, then that is the reason why it never happened on your MK4S. The bowden tube in the Core ONE restricts the sideways movement of the filament and when the extruder pushes it back by 5 cm, it comes out by 5 cm on the other end. That is how bowden tubes work. 

I have my filaments in overhead dryboxes with bowden tubes feeding in a straight line directly into the printhead. The bowden tube is not fixed to the printhead, so when the filament is being pushed back it doesn't push back the filament through the tube. When something like your situation happens, I have to open the drybox to fix it, which is a hassle. This is how it that looks:

But that is not an option for you, since the Core ONE has the tube fixed to the printhead.

 I might just try that before i print  anything to be sure that holder is really the culprit. 

I can already tell you that this will not help. It's simple 'filament mechanics': you can not push it back onto the roll. It will unwind and fall off in the same manner. That's why there is a filament buffer and all kinds of auto rewind spool designs for use with the MMU3. 

If I were you, I would take the pragmatic approach: just put the filament back on the spool and don't worry about it. Like I imagine every one of the thousands of Core ONE owners do. I have not heard anyone complain about this.

iftibashir: what holder do you use?