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MMU2S Messing With Retract Settings??  

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Ewest
(@ewest)
New Member
MMU2S Messing With Retract Settings??

This is a bit of a lack of understanding on my part about how the MMU2 Works.  Does the MMU let go of the filament once the extruder grabs onto it or do the two drive motors work in tandem the whole print?

Either way I am having issues tuning out some stringing with PETG and I am wondering if the MMU2 is messing with it. On my other MK2.5s with no MMU2 the same setting produce minimal strings, however on the MMU2s Mk3 the stringing is so bad the thicker whiskers that grow are present. 

 

Retract: 2mm (max recommended by prusa) (Set under filament overrides) 

Retract Speed: 50mm/s (Set under filament overrides) 

Travel Speed: 200mm/s

Temp: 250C

Cooling always on, Min 30%

Posted : 05/10/2021 7:05 pm
JoanTabb
(@joantabb)
Moderator

I use 0.4mm retraction. with my MMU2

the MMU2 hands over control to the Mk3 Extruder as soon as the filament sensor acknowledges arrival of the filament, 
from that moment on, the MMU should select a null position where the pressure roller is inactive for that filament
similarly when the printer unloads the filament, the MMU takes control as the filament leaves the filament sensor.  
Have you tried a lower extruder temperature to control the stringing?

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 : 05/10/2021 7:14 pm
Ewest
(@ewest)
New Member
Topic starter answered:
Reply

 

Posted by: @joantabb

I use 0.4mm retraction. with my MMU2

the MMU2 hands over control to the Mk3 Extruder as soon as the filament sensor acknowledges arrival of the filament, 
from that moment on, the MMU should select a null position where the pressure roller is inactive for that filament
similarly when the printer unloads the filament, the MMU takes control as the filament leaves the filament sensor.  
Have you tried a lower extruder temperature to control the stringing?

regards Joan

I have not, I might play around with temp some but do not want to give up too much layer adhesion. Im also just confused why on one printer the stringing is far worse than the other. 

Posted : 05/10/2021 7:21 pm
JoanTabb
(@joantabb)
Moderator

Printers are like humans, they are all different. 
your temperature control is handled by thermistors which may not be accurate when connected to your controller. 
so it is entirely possible that the displayed temperature is not the actual temperature of your hotend. 

usually they are pretty close, but they do have a tolerance... as does the controller board, so occasionally you may have issues. similarly. different rolls of filament may have different characteristics
the white filament in this print, was awful...

I ended up printing it at 170Centigrade.

Temperature issues can be especially problematic, if you, or someone else have replaced your Semitec thermistor, with a different manufacturer's thermistor. the resistance slope may be good at 25Centigrade, but may be significantly different above and below that temperature

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 : 05/10/2021 7:35 pm
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