MMU2S keeps “needing attention” - filament getting scraped by idler
 

MMU2S keeps “needing attention” - filament getting scraped by idler  

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Pixelpeeper
(@pixelpeeper)
New Member

Just finished my setup of the MMU2S, coming from MK3S. It’s been frustrating.

To get things going, I ran first layer cal on all the filaments and after some initial pointy-end issues, I tested them all OK.

On my first 2 material print (PLA and Prima Select PVA+), the printer would run fine for about 5-6 layers, then encounter issues when switching filament.

I find myself having to undo the Festo on the MMU end and when I pull the filament out to check and cut a new tip, I find two issues: in all cases, the gear in the idler seems to have dug into the filament (idler spring not set right?) - see attached photo. In a quarter of the cases, the tip gets a bit stuck.

Where and how can I start troubleshooting?

thanks!

Filament ends pulled from MMU end of PTFE

Best Answer by stewartr:

Have you checked that the screws holding the MMU idler housing aren't too tight? From your description it sound like that's the issue here. The normal advice is that they should be flush with the top of the casing and then tightened two turns. In your case maybe less perhaps. When you pull out the filament from the front of the MMU it shouldn't have too much friction; it's hard to describe, but you shouldn't need 'too much' force. Maybe the PTFE feeder tubes are squeezed too much if this is the case - at the MMU end, or the buffer end if you're using that. Was the filament easy to feed in when you first loaded it?

Posted : 01/01/2021 9:04 am
stewartr
(@stewartr)
Eminent Member

Have you checked that the screws holding the MMU idler housing aren't too tight? From your description it sound like that's the issue here. The normal advice is that they should be flush with the top of the casing and then tightened two turns. In your case maybe less perhaps. When you pull out the filament from the front of the MMU it shouldn't have too much friction; it's hard to describe, but you shouldn't need 'too much' force. Maybe the PTFE feeder tubes are squeezed too much if this is the case - at the MMU end, or the buffer end if you're using that. Was the filament easy to feed in when you first loaded it?

Posted : 01/01/2021 8:09 pm
Pixelpeeper
(@pixelpeeper)
New Member

Hi, and yes, thanks for clueing me in! Yeah, it was the idler, but I’m still not sure that it was too tight.

I undid the idler springs to blow out the filament shavings in there, and set the screws like you mentioned and now it’s experiencing more layers before stalling.

This time, it seems the tips aren’t forming properly and have that wisp that gets caught.

I’m starting to suspect that the tips could not make it down the PTFE and the bondtech was shaving the filament trying to push the filament through.

I’ll check the print temps and increase the cooling moves like the manual mentions and see how that works out.

Thank you and happy new year!

Filament tips

Posted : 01/01/2021 11:35 pm
JoanTabb
(@joantabb)
Moderator

@pixelpeeper

what happens if you lower the temperature a little?

the tips should be less stringy. 

I am out of date with the MMU2S because of the Covid issues, I haven't seen the printer for 9 months...

Other folk may be able to help more. 

IIRC I used to increase the ramming time to 4seconds,  and increase the cooling moves to 4 

regards Joan

I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK...
Posted : 02/01/2021 1:34 am
Pixelpeeper
(@pixelpeeper)
New Member

@joantabb

Hi there and thanks - I feel compelled to reply because I have managed to solve the problem after trying a bunch of approaches:

  1. Yes, lowering temps worked out. I had about 245-250 on my notoriously stringy eSUN PETG, and after another temperature tower, I tried 236C instead and the PETG is surprisingly well-formed. There's still an occasional string, but the it's far more successful, and I'm no longer intervening - the string sometimes just gets pushed out at the idler or isn't sufficient enough to gunk the bondtech at the extruder.
  2. IR sensor calibration had to be redone. I read a bunch of forum pages and reddit and a lot of them complained about the calibration, so I redid it, even though I just assembled and calibrated it. Turns out that the IR readout in the menu wasn't stable when I tried this time, so I started over and now it's super-reliably reading it.
  3. Initial tips are a lot sharper because I switched to using a flush wire-cutter instead of the provided yellow ones (which limit the angles to about 45 degrees). The sharper tips are now reliably loading.

Overall, I'm having a much better time with the MMU2 now that the setup is up and running. If I can suggest, do consider rethinking the IR sensor calibration - I'm hoping for more certainty that I got it right.

Again, thanks for everything - am grateful for the help I got!

Posted : 06/01/2021 6:46 am
pcweber
(@pcweber)
Estimable Member

@pixelpeeper

Hi, 

I have gotten to know the mmu2s quite well since I've had it for over a year now. 

I had some intermittent flashing lights errors which finally came down to the MMU pcb. 

Other errors came from the selector rubbing against the part where the selector rubs against. I polished this part until there was no more binding. I also reprinted the carriage case it came with a layer shift when it was new. 

Until the filament travel was smooth I cleaned the path through the extruder.

To get the IR sensor perfectly correct, I did the mod where an smd led is soldered on top of two smd resistors on the IR board. Drilled a tiny hole to view the leds condition. Occasionally I've had to adjust the chimney position, but it has simplified troubleshooting.

Adding a coupler nut to the idler barrel eliminated the occasional loosening of the two screws. 

In my opinion the mmu2s is a great concept that could be refined. Learning how to eliminate the problems can be a grueling task; however, there is great satisfaction once the unit is operating optimally. 

I have to thank all who've placed their knowledge on this forum that's helped me overcome my issues. 

Stay safe and healthy, Phil...
Posted : 13/03/2021 3:46 pm
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