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Unresolved PETG warping on large parts.

Discussion in 'Troubleshooting' started by Nathanfish, Nov 22, 2015.

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  1. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    The longer Y axis just means more potential steps for full travel.
    The math for how many steps is needed to travel X amount is the same.

    ?
    I doubt that over extrusion will affect the dimensions in a consistent way... it would mean more bulging layers, so in that regard they might be slightly over-sized. You should be able to see that looking at the sides...
     
    #61 mark tomlinson, Dec 7, 2015
  2. WheresWaldo

    WheresWaldo Volunteer ( ͠° ͟ʖ ͡°)
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    Just so you know, most plastics shrink when cooled, some by significant margins (ABS for example). Also they expand when heated, again some by significant margins (PLA for example). Any very small discrepancy in the mechanics multiply over the growth in model size. I know that if I want a part to be dimensionally accurate in PETG, on my printer I need to scale X and Y by a factor of 1.014, Z does not shrink as much since the layer height is a small fraction of the extrusion width so I don't scale it at all.
     
    #62 WheresWaldo, Dec 7, 2015
  3. Nathanfish

    Nathanfish Active Member

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    I just find it odd that the X axis is within .001 at 2.850" but Y is off so much. If it was a shrinking error i would assume it would be consistent. I'm going to go home after work and calibrate the Y axis and hopefully get it dialed in.
     
    #63 Nathanfish, Dec 7, 2015
  4. Nathanfish

    Nathanfish Active Member

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    So i'm still waiting on the first layer of this 100mm test cube but it's coming in around 101.75mm on Y. Obviously i need to wait for it to cool and remeasure before i do anything but I don't see an option in simplify to scale just one axis. Is this only done in the firmware?
     
    #64 Nathanfish, Dec 7, 2015
  5. Mike Kelly

    Mike Kelly Volunteer

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    Have your calibrated your E steps per mm?
     
    #65 Mike Kelly, Dec 7, 2015
  6. Nathanfish

    Nathanfish Active Member

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    still researching.. 100mm cube came up very close to 100mm on X and 101.65 on Y. So definitely should have checked that before 40 hours of printing..
     
    #66 Nathanfish, Dec 7, 2015
  7. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    If the Y drive belt is the same number of teeth per inch then it should be fine.

    I'd say check the POTS calibration for the Y stepper driver, but I would totally expect if it were under-current that it would under-step (drop steps) never add extra ones. Calibration of the Esteps as @Mike Kelly suggested will rule out over extrusion. Although I am having a hard time imagining that would cause your symptoms--but that's just my thinking :)
     
    #67 mark tomlinson, Dec 7, 2015
  8. Nathanfish

    Nathanfish Active Member

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    Well i changed my steps per mm in the firmware from 80 to 78.7 and it's coming out right at 100mm now. I need to reprint this 12hr tool for work is there anything else you guys would check or should i go for it? I brought home the aluminum blank so i guess i can check to make sure the two alignment dowels line up after the first few layers.

    So frustrating! I really appreciate all the help.
     
    #68 Nathanfish, Dec 7, 2015
  9. Mike Kelly

    Mike Kelly Volunteer

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    Don't do this. The 80 steps per mm is a calculated value. Tom uses the analogy that adjusting this is like having the air low on the right side tires in your car, so you stear left to compensate for it. It's not fixing the problem but rather moving the problem somewhere else.

    Watch these 2 videos:



     
    #69 Mike Kelly, Dec 8, 2015
  10. Nathanfish

    Nathanfish Active Member

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    Yeah i watched those videos but couldn't figure out how else to do it other than that. So if i leave that at 80 do i just scale my model on Y to compensate?
     
    #70 Nathanfish, Dec 8, 2015
  11. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    Yes, agree. There is a spreadsheet on the RepRap site where you can even enter all of the pertinent info and it will tell you what these values are. It is a mechanical dependency.
     
    #71 mark tomlinson, Dec 8, 2015
  12. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    Again you are treating a symptom without curing the disease. If it is not accurately stepping 80 steps/mm then something is mechanically wrong on that axis.
     
    #72 mark tomlinson, Dec 8, 2015
  13. Nathanfish

    Nathanfish Active Member

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    What if for some reason the belt i ordered isn't exactly the same as what came stock? Would that be the proper way to adjust it? That's the only thing i can think of that might be wrong but i was fairly certain I ordered the same thing as stock.
     
    #73 Nathanfish, Dec 8, 2015
  14. Nathanfish

    Nathanfish Active Member

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    #74 Nathanfish, Dec 8, 2015
  15. Mike Kelly

    Mike Kelly Volunteer

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    Wait you replaced a timing belt? Why did you do that? Needs to be a GT2 belt
     
    #75 Mike Kelly, Dec 8, 2015
  16. Nathanfish

    Nathanfish Active Member

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    Well I think i found my problem then. I used that for the Y axis belt. Can't remember where i got the link from but i just ordered without much research on my own. It looked very close to what was stock so i assumed it was right, i'll check closer when i get home. So now knowing that i had the wrong belt should i order a GT2 belt to replace it or would keeping my steps per mm at 78.7 be sufficient?
     
    #76 Nathanfish, Dec 8, 2015
  17. WheresWaldo

    WheresWaldo Volunteer ( ͠° ͟ʖ ͡°)
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    #77 WheresWaldo, Dec 8, 2015
    mark tomlinson likes this.
  18. Nathanfish

    Nathanfish Active Member

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    Cool, just overnighted me one. Thanks again guys. Hopefully this print i have going turns out. I'll know here in an hour or so.
     
    #78 Nathanfish, Dec 8, 2015
    mark tomlinson and Mike Kelly like this.
  19. Pergo

    Pergo Member

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    Same here I also use the esun PETG and love it.. I notice that the tell tale sign is keep moving the temp up (1C increments) until the filament has a sheen. 1C below that temp it slightly has a dry look. when you see the sheen or shine, you got the right temp. For the Robo3D R1 (Sep purchase) with my E3Dv6 upgrade, I see the perfect temp for esun black PETG to be 249C Pine Green seems 1C lower.
     
    #79 Pergo, Dec 22, 2015
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