MMU2 - First print worked right up until the retraction of the filament.
Having meticulously assembled the unit I was ecstatic that it appeared to work first time, then the filament stopped moving half way through the retraction.
I removed the filament, and tried again, this time it got stuck halfway between the extruder and te MMU2, removing the filament revealed half moon chunks taken out of the filament at regular intervals.
It now no longer seems to be able to pull the filament into the MMU, with a red light. flashing over the slot.
Pushing the filament manually will turn the led green, but it will still not 'bite' take the filament.
Open to ideas please
RE: MMU2 - First print worked right up until the retraction of the filament.
It can now bite the pla and drags it up to the top of the white tube, but then it goes no further (same on nozzles 1 and 2), there are no blockages and I have even recalibrated the gears on the idler to ensure they are all true centre.
RE: MMU2 - First print worked right up until the retraction of the filament.
It sounds like the extruder gear is gripping the filament too tightly at points where it's feeding it down to the extruder. Hence grinding chunks out of it.
There's a few things to check; are the tensioning (spring loaded) bolts on the MMU adjusted correctly? Flush with the body, and then two turns in seems to be a good starting point. Is the path of the filament from the spool, through the buffer (if you're using it) and through the MMU body smooth? With the MMU opened you should be able to pull the filament through without having to tug on it, or apply too much force. Likewise pushing it back.
RE: MMU2 - First print worked right up until the retraction of the filament.
@stewartr
I've adjusted the tensioning spring with less rather than more as my focus (flat with the top then max of 2 turns, the buffer seems sound.
I'll try pushing it back and forth through the buffer and note how much force I am using.
RE: MMU2 - First print worked right up until the retraction of the filament.
It seems to be taking too much force to move the filament backwards and forwards in the MMU, with more force needed on the return.
RE: MMU2 - First print worked right up until the retraction of the filament.
That could well be your problem then. The PTFE tubes are getting held too tightly possibly? Either where they enter the back of the MMU body, or at the buffer end. You could try fiddling about with the tightness of all the screws, or print some new (improved) parts. There's a discussion on the subject in this thread;
Although that may not have turned out the be the complete solution. It never hurts to reduce friction at the back as much as it can be. I printed the MMU body part and the parts for the buffer-MMU end. At the very least, using festo-style couplers helps remove things from the printer.
RE: MMU2 - First print worked right up until the retraction of the filament.
@stewartr
I printed a replacement part to hold the tubes at the back using FESTO couplers, that solved half the problem.
My new problem is that the filament is getting stuck leaving the extuder as the head is too big for the pipe.
RE: MMU2 - First print worked right up until the retraction of the filament.
Odd that that's just started happening. Are you using the same filament? That's usually down to temperature. With the MMU attached the printer has to shape the filament end as it comes out of the nozzle so that it can be reinserted again later; before, you'd have to cut the end before reloading it. It does this by pushing the filament back into the end of the nozzle after cooling it a bit. I've used a few filament types and just using the Prusament setting have always worked (although with some brands the tip was a bit stringy, but it still reloaded fine). The easiest thing to do would be to try adjusting the temperature a little bit. You shouldn't have to change it enough to affect the print quality - try adjusting it on the LCS screen first to see if that'll help then update the filament setting if you find something that works. Other things you could try are Filament Settings / Advanced: the MMU toolchange block of settings. Maybe Number of cooling moves (although I'm not sure exactly what this will do for you)? If you're feeling adventurous: Ramming parameters (it will warn you all about fiddling about in there, so be prepared for things to fail).
To be honest, I've not had any issues in this area. I generally use Prusament with Prusament settings and everything's fine. I've got some old PLA that prints at significantly lower temperature and that works out even if I forget to change the settings to that.