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MMU2s breaking filament during filament change  

Andy Forsberg
New Member
MMU2s breaking filament during filament change

I'm having a failure mode rather consistently during filament change:

  • MMU2s thinks it fully removes previous filament
  • selector moves to a new position
  • the tip of the filament string gets jammed between the selector and selector body, blocking the next filament 

I've checked:

  • The FINDA seems to be properly calibrated

It seems like:

  • either the MMU2s isn't retracting the filament far enough
  • or the cut-off blade is snagging the filament and pulling it out

I'm in the middle of a benchy MMU print right now, and the first 10mm or so of the benchy was fine- now this is happening in every filament change. I'm able to recover by unscrewing the selector stepper, pulling it over 25mm or so, then pulling out the broken piece of filament.  


I'm trying to extract the blade from the selector during this print to see if this will help.


Posted : 05/10/2019 4:44 pm
RE: MMU2s breaking filament during filament change

the filament shouldn't be stringing.  
Is your filament fresh and dry? 
is your temperature for the extruder too high? 

are you using the latest firmware and slicer?

are you doing enough cooling moves?
are your ramming settings good?


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 : 05/10/2019 5:14 pm
Andy Forsberg
New Member
Topic starter answered:
RE: MMU2s breaking filament during filament change


  • Removing the blade seemed to have no impact at all. (blade removed, blade retention clamp replaced)
  • I took a look at the FINDA calibration again, and moved it up as high as possible. 

So far the FINDA re-calibration seems to have done the trick- many exchanges so far without issues.

Posted : 05/10/2019 6:26 pm