PLA jams -- how can I prevent this?

Discussion in 'Calibration, Help, and Troubleshooting' started by jet, Jul 2, 2016.

  1. jet

    jet Well-Known Member

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    I've never worked with PLA before, so it's entirely possible I'm just doing it wrong...

    I have a reel of SainSmart 1.75mm PLA in Fluorescein green. I can get a great print, but only once. When I go to do another print it's completely jammed and I have to clean it out (some times take it apart) to get another print. I let the unit cool between prints and I'm wondering if I should do a massive retraction at the end of a PLA print to keep the nozzle from getting clogged.
     
  2. Paul Winter

    Paul Winter Well-Known Member

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    Nozzle temperature too high, and the filament is burning inside the nozzle?
    When the printer is printing, the PLA is moved through pretty quickly, and doesn't have time to burn.
    Try pulling the filament back out a few minutes after a print, and check to see if there are any charred or black bits coming back out on the end of the filament.
    Another issue might be the particular colouring agent in the filament aggregating at the nozzle.
    What happens with other reels of PLA (if you have any)?
     
  3. mike01hu

    mike01hu Well-Known Member

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    Reduce your in-print retraction to between 1.5 and 2.0 and add about 0.25 Z-lift and do a purge and long retraction at the end as you said, the purge ensures that the filament is not too soft when the long retraction takes place, so that no melt is drawn back into the heat break. This is good practice for the stickier filaments such as PLA and its variations. Alex's end code incudes this and I have kept this in my profiles.
     
    #3 mike01hu, Jul 2, 2016
    Last edited: Jul 2, 2016
  4. Alex9779

    Alex9779 Moderator
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    Actually this end code is just based on the ram purge. I thought it could be a good idea because I don't wanna have my nozzles dripping when I start a new print so I moved the ram purge to the end too.
    Don't forget you have to undo the massive retraction when you start a new print...
     
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  5. jet

    jet Well-Known Member

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    I think I have Alex's, maybe I should retract 50mm or so?

    ;purge extruder 0
    T0 ; select extruder 0
    G1 E25 F400 ; extrude 25mm
    G1 E-14 F4000 ; retract 14mm very fast
     
  6. jet

    jet Well-Known Member

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    Ok, pulled out the PLA and I'm stunned at how little of a melted bump on the end of filament will be blocked by the back of the .4mm nozzle.
     
  7. mike01hu

    mike01hu Well-Known Member

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    It's not so much the little bump it's the fact that when near fluid PLA is very sticky and adheres to the heat break; you don't need much to stick to cause a jam. You wouldn't think that when is does not stick to the bed! :(:D
     

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