Pressure advance limits?



  • I have a RailCore II that is pretty well tuned. Can run at 10,000mm/sec^2 acceleration on XY and if the material is good enough, print at 300+ mm/sec.

    My problem is, I can only seen to get pressure advance to mitigate ghosting at acceleration of 2000. I tried tuning for 4000 and there are some decent bands, but it never disappears like it does at 2000.

    I've printed ghosting tests at true 200mm/sec with 2000 acceleration and they're so smooth, they look like a an animation cell.

    Long story short, is there a limit to how much pressure advance can help?

    My extruder, BMG with 0.9 motor, acceleration is 6000.
    Jerk for XY is 1500
    Jerk for extruder is 600.

    Any ideas? This print has 10 bands of PA increments, increasing from bottom to top.

    IMG_20200824_215136.jpg

    IMG_20200824_215124.jpg

    IMG_20200824_215102.jpg



  • @gnydick I think you're confused between Pressure Advance and Dynamic Acceleration Adjustment.

    Pressure advance aims to compensate for the elasticity of the filament and the extruder system which can cause under-extrusion whenever the extrusion rate is increasing, for example at the start of a straight line when the nozzle has to accelerate from zero or near-zero speed, or over extrusion when the extrusion rate is decreasing.
    https://duet3d.dozuki.com/Wiki/Pressure_advance
    It is mostly effective at stopping under/over extrusion blobs at sharp corners. If you want to calibrate this, I'd recommend the steps at the bottom of the wiki page above.

    Dynamic acceleration adjustment is used to help ringing/ghosting in your prints by tuning out the frequency you set. I think this is what you want 🙂
    https://duet3d.dozuki.com/Wiki/Gcode#Section_M593_Configure_Dynamic_Acceleration_Adjustment

    I'm guessing you've already chased after all the mechanical things to aid ringing (belt tension, making sure your pulley mounts/axles are solid, reducing mass on your moving gantries etc). If after all of this, you find you can't get raise your printing accel as much as you want, you can always use your slicer to vary it by feature type (I know PusaSlicer, Cura and IdeaMaker all have this at least). That way, you can set much higher accelerations for infill, but drop it for internal/external perimeters to maintain quality. In Cura & IdeaMaker, you can also do the same with Jerk.



  • @engikeneer thanks. Yes, I'm aware of the distinction. From my pictures, you can see the ghosting only happens after sharp feature changes. That's why I believe it's PA.


  • Moderator

    @gnydick said in Pressure advance limits?:

    Jerk for extruder is 600.

    Increasing extruder jerk is generally recommended to allow PA to function better. Try 3000.



  • @gnydick said in Pressure advance limits?:

    @engikeneer thanks. Yes, I'm aware of the distinction. From my pictures, you can see the ghosting only happens after sharp feature changes. That's why I believe it's PA.

    I may be missing something, but I don't believe its PA, and I do believe it is DAA, M593. Have you configured M593?

    I think you're conflating a PA "fix" at 2000 mm/s^2 when really the system doesn't create ringing at 2000mm/s^2.

    I would recommend running your same test, but with an appropriate value of M593 configured. Verify the speed at which your outer perimeters are set to (stock print speed doesn't always equal the perimeter speed... make sure you double check), and divide that by the "peaks" of the ghosting ripples.



  • @sebkritikel what am I supposed to do if the ghosting is not the same frequency on different parts of the print?

    The front of the print in these images has 2.5mm between peaks. the back surface as 1.5mm.

    I don't think this is DAA.



  • @gnydick said in Pressure advance limits?:

    @sebkritikel what am I supposed to do if the ghosting is not the same frequency on different parts of the print?

    The front of the print in these images has 2.5mm between peaks. the back surface as 1.5mm.

    I don't think this is DAA.

    With DAA, you want to target the lower frequency, in this case whatever your frequency would be with the 2.5mm peaks (assuming 200mm/s / 2.5mm = 80hz) rather than the frequency at 1.5mm.

    Some artifacts specifically located at the corners can be improved by your selection of PA, but I don't see how these areas would be improved by PA values.
    48d782e7-4734-44fa-b206-05514cd10a31-image.png
    cd58bd0b-091a-41fa-b61c-f26ff63f71b7-image.png

    Would be interesting to check the ringing on a longer wall section, like 150mm or so.

    I don't have any advice on your PA specific testing, but would be interested in seeing how it turns out.



  • @sebkritikel I'll print some bigger sections. WRT to the artifacts around the logo, PA isn't limited to "corners." A corner is just a sharp directional change. Any sharp direction change will be considered.


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