Higher speed PA tuning

  • Hello!

    I've been having a bit of a challenge getting the balance between speed, jerk, PA, and extrusion multiplier all dialled in for functional prints.

    My latest case I was printing at the following settings with a calibrated Hemera and Volcano block, 0.6 nozzle, PLA at 205C

    • Perimeters 120
    • External perimeters 60
    • Solid infill 100
    • Print acceleration 1000
    • Jerk 300 mm/min
    • Extrusion width 0.72
    • Layer height 0.2
    • PA 0.042
    • Extrusion multiplier in DWC 88%

    So I've found that my PA is a bit too high, and I'm ending up with underextruded perimeters on curves as PA would behave normally with these settings.

    My issue is that if I bump up the extrusion multiplier back to the calibrated normal percentage, I end up with overextruded short infill segments that frequently lead to nozzle collisions because of all the extra material. The filament itself is at 1.74mm so it can't be due to variation in filament width alone from my guess.

    Here's a shot of what that looks like when underextruded:

    You can clearly see the voids in the circular perimeters from the PA doing its thing as expected. Straight segments come out perfectly, and the top surface is otherwise flawless.

    So when I decrease PA or even disable it entirely, at the same reduced extrusion multiplier, the perimeters come out normally, but I still end up with overextruded short infill sections.

    What should I try next? I'm guessing I should print infill sections slower perhaps..

  • I dont think that this issue is due to PA. PA is only there for giving a consistent extrusion width while accelerating.
    Are you printing the outer or inner perimeters first?
    The plastic shrinks as it cools and holes tend to contract.
    If you print the inner perimeter first, the outer perimeter sort of pulls away from it while printing.

    Try printing the outer perimeter first, this will reduce that effect. A side effect is that you will get better tolerances.
    If that doesnt help, increase your flow factor from 88 to maybe 93 % and to compensate try printing with just 95% infill.

  • Hey

    I am printing external perimeters first. And PA works at the start and the end of segments to even out flow..

    But thanks for the tip. And infill percentage doesn't make a difference here cause it's solid infill and perimeters...

    And if you look at the straight segments you can see that they're slightly underextruded since the multiplier was a little too low too when I was trying to compensate. The empty spots are all where the print was either retracting or going around a corner.

  • I would suggest trying to print with an actial flow closer to 100%. 88% sounds like there might be something wrong with your settings or e-steps, and it does in fact cause underextrusion.
    When you print the infill faster than the perimeters, pressure advance compensates a little too much on the faster sections and too little on the slower. I would recommend to always tune your PA for the fastest sections, as the slower sections do not exacerbate the overextrusion during the accelerating section as much.

  • Moderator

    Retune your extruder: https://duet3d.dozuki.com/Guide/Ender+3+Pro+and+Duet+Maestro+Guide+Part+4:+Calibration/40#s165

    Retune your PA: https://duet3d.dozuki.com/Wiki/Pressure_advance?revisionid=HEAD#Section_How_much_pressure_advance_to_use

    Please post the rest of your speed settings from config.g

    I also use a 0.6 nozzle and find that I need to increase jerk a bit to get cleaner solid infill. I also find that it's prone to over extrusion in short sections with rapid back and forths.

    Using Cura and changing the top/bottom pattern to lines instead of zigzag also seems to help a bit as it will introduce a full extruder stop or even retraction at the end of the line rather than just a short extrude. Not an option with prusa slicer.

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