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How to fix: after 10-15 minutes the hotend temp regulation goes bad

Discussion in 'Mods and Upgrades' started by Lance Weston, Apr 7, 2020.

  1. Lance Weston

    Lance Weston Active Member

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    I only had one R2 where the temp regulation of the hotend became bad after 10 to 15 minutes. On that machine it got worse with fan speed. That machine was the only machine that I had forgot to put the hotend heat shield on. When I tried a new shroud ( moved the IR board up ) I put back on the heat shield and all of my regulation got better and the 10 to 15 minute mark no longer mattered. I have a couple of shrouds with heat shields posted on thingiverse. If anyone wants, I will post my latest shroud and variable pressure arm. Picture of heat shield attached.

    I suspect it has to do with how high the print head is off of the print, but I only know the remedy, not the cause.
     

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  2. tkoco

    tkoco - -.- --- -.-. ---
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    The only factor which I can think of is the PID control loop is regulated too tightly. And once the heater block gets outside of the ability of the PID control loop, then could result in the loss of control. Is this R2 the one where you did a modification of the PID calibration routine?
     
  3. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    That sounds like in the one instance the parts fan might have been cooling the hotend -- or something at least was inducing a lot more air flow over the heater block. That will make things "intersting"
     
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  4. tkoco

    tkoco - -.- --- -.-. ---
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    And it might be model dependent, possibly redirecting the cooling fan air to the hot-end, or not as printing progresses.
     
  5. Lance Weston

    Lance Weston Active Member

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    It is an interesting problem and when I researched it, I found many people with the same problem. The parts that I was printing were parts that are identical from bottom to top so the cooling profile is identical except for height. Yes, it is my modified smoothing constant, and the 15 minute mark did not bring about and decrease in regulation as long as I had the heat shield.

    When using the PID wizard the fans are off and not affecting the hotend. The shield works the same way.
     
  6. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    Yea, without being hands-on to observe it directly the cooling air-flow as a source of the problem is just a targeted guess.
    I have seen it when you get too much part cooling as well as when the part cooling is misdirected as nozzle cooling :)

    Only you can make that call.
     
  7. Lance Weston

    Lance Weston Active Member

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    This is the shield ,in action (attached). I am tuning into a new plastic. It does not allow any of the cooling fan flow back onto the hotend heater.
     

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  8. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    It is not the heater block itself you want to avoid cooling (although -- sure -- you do want to avoid cooling it too) rather the nozzle. Parts cooling fans can be mis-aimed and flowing air across the nozzle which will suck some of the heat away. This is why on most printers the parts fan is on the back side of the X carriage so that it is far enough away to only direct flow at the bed. Inevitably some will hit the nozzle, but it is when folks upgrade to more or larger fans that it becomes an issue (generally).

    Also the hotend can matter. For example the R1 used the hexagon as well by default and the parts cooling fan was aimed correctly for that hotend. If you just directly swapped to the E3D it was longer and the parts fan is now only cooling the nozzle.
     
  9. Lance Weston

    Lance Weston Active Member

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    Here you can see my temp regulation with a shield. This is with the Partsbuilt proto with the same electronics as the R2. I get +/- 0.3C regulation, and it extends all the way out. After 15 minutes no change, like you can see on my other pictures.
     

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  10. Lance Weston

    Lance Weston Active Member

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    This picture better shows what I am doing. All airflow points down, only the tip of the nozzle is in the air flow. I use an E3D wade with a 30 mm cooling fan. I like the wade because I pick them up from eBay for $8 when lucky. I take the thermistor off and use it. I do not use the standard heater block, I machine my own out of brass. Brass has three times the mass but not as good heat transfer as aluminum. In the Marlin software.I modified the code to offer the 3950 thermistor that is in these cheap clones. It is only a few degrees different from the Robo thermistor, but why not take it into account. I also use 40w heaters.
     

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  11. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    What happens when you print with no parts cooling fan running? Does it behave the same way?
     
  12. Lance Weston

    Lance Weston Active Member

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    Have a print running for another 3 hours. When finished will run without fans and post result.
     
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  13. Lance Weston

    Lance Weston Active Member

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    This is with no fans running. I can see at 18 minutes out a very slight increase in change. It went from a +/- 0.3C to +/- 0.4C.

    I also went to 48 mm steppers and increased the bias from .9v to 1.1v, a 20% increase in current. I thought this might reduce my ghosting. It did not. When the Partsbuilt board is released you will have more tuning options because the stepper current is adjustable allowing larger or higher current steppers.
     

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  14. tkoco

    tkoco - -.- --- -.-. ---
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    By any chance, do you have some sort of post-processing enabled in your slicing software?
    The last image posted suggest a post-processing issue rather than a regulation issue. I would expect a regulation problem to show as an erratic wandering line instead of the step function which is displayed.
     
  15. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    Bear in mind thermistors (the 100k ones) are generally only accurate with a 0.20 Celsius range. So if it fluctuates that much or less it is just "noise"

    Thermocouples tend to be more accurate, but probably still within 0.1 C
     
  16. Lance Weston

    Lance Weston Active Member

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    The first layer is printed hotter than the rest of the print for adhesion. I use cura 4.4.0
     
  17. tkoco

    tkoco - -.- --- -.-. ---
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    Try removing all post-processing and see what happens. BTW, Cura is now version 4.5.0
     
  18. Lance Weston

    Lance Weston Active Member

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    I do not know what you are referring to with post processing. In the the cura file I control temp, speed, line width and many other settings. I could send you my cura file. I do not automatically update cura because in the past they have released versions that did not work.
     
  19. tkoco

    tkoco - -.- --- -.-. ---
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    In Cura, Extensions -> Post Processing -> Modify G-Code. Delete any scripts / instructions within the box.

    And you are correct about versions of Cura having problems. I generally try the newest version of Cura. If I run into problems, I either post a work-around or post an alert explaining the defect.
     
  20. Lance Weston

    Lance Weston Active Member

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    In Cura, Extensions -> Post Processing -> Modify G-Code Nothing there
     

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