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Solved Pla not feeding after 45 minutes

Discussion in 'Troubleshooting' started by John Pearsley, Mar 20, 2021.

  1. John Pearsley

    John Pearsley Member

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    We have a problem with the PLA not feeding after about 45 minutes. We have a R1+ with a new Ramps board and new hotend (inc thermistor and heater). We are using PLA at 210 C. The PLA stops feeding even while the hobbs bolt is rotating. We sometimes find a bubble in the PLA at the top of the hotend which stops the feed but we don’t hear the hobbs bolt clicking or see the nicks in the PLA. The hot end cooling fan is warm to the touch. When I try to pull the PLA back out of the hotend while the temp reads 210 C, it acts like the hot end is not hot enough and the PLA sometimes breaks leaving a curled section about the length of the hotend tube. Attempts to measure the temperature externally (handy steak thermometer) indicates the temp is at least 186 C. (I don’t think there is a good thermal connection so I think it just indicates the temp is high). The PLA bubble and warm fan makes me wonder if the hotend has heated up too much at the top so it is not filling the reservoir at the bottom. Any suggestions?

    thanks to Mark. When we removed the hot end cooling fan its bearing were not good. It would rotate but slowly. We are replacing it with a new one. problem solved.
     
    #1 John Pearsley, Mar 20, 2021
    Last edited: Mar 21, 2021
  2. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    What you are describing is called heat creep

    In a normal working hotend the filament comes down the hotend through the finned section (cold section -- should be slightly better than room temperature in the worst case) through the heat break (the narrow part) and into the melt zone. This is the only place the plastic should actually be melted -- just before it is pushed out the nozzle.

    With heat creep the heat break fails to do its job (keep the heat in the heater block) and the cold section heats up and you get melted plastic in or above the heat break.

    Why this can happen? Usually on the all-metal style hotends (Hexagon, E3D, etc) the fan attached to the side of the hotend blows room temperature air across the finned section to keep it "cold" relative to the heater block. If that fan is not working or there is something else awry with the hotend (bad assembly can do it if the heat break is too buried in the heaterblock or the finned section to do its job) then you have problems. This is also why it is not happening immediately. It takes time for the heat to "creep" up the hotend and cause problems.
     
  3. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    So things to do:
    1) make darn certain the little hotend fan is running all the time and full-speed. If it is not -- replace it.
    2) make sure the hotend is assembled correctly. That you can see the heat break and the narrowest section is centered between the heater block and the finned section.

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