Pressure Advance - no visible impact - what am I missing?



  • After seeing significant improvement using Linear Advance on my MK2, I decided to try Pressure Advance on my Kossel Mini with DuetWifi running 1.21RC2.

    I printed a total of 5 20mm XYZ cubes. Oddly, while I believe I heard the influence of PA (especially at 0.25 and 0.35), I can't say I could see the difference.

    Off all 5 cubes, the top surface of one looks a bit more dull. I think that is because I printed that cube at a different temperature. That is also the cube without PA configured.

    The material is MakerGeeks PLA. The cube was sliced with S3D 4.0. My extruder is an E3D Titan. I had just calibrated yesterday before started the PA testing.

    I inserted the following command in my start GCODE:```
    [[language]]
    M572 D0 S0.25 ; Pressure Advance - 2/24/2018

    Changing the S parameter as shown below the images, but between: (no PA), 0.25, 0.25, 0.10, 0.35.
    
    You can see larger images from the Imgur album: [https://imgur.com/a/sZj9A](https://imgur.com/a/sZj9A)
    
    Any ideas? (sorry that the lighting is not ideal)
    
    ![](https://imgur.com/EPGLKXi.png)
    ![](https://imgur.com/RaeoEfo.png)
    ![](https://imgur.com/uThpI4a.png)


  • Any noticeable increase in print times ? Did you mod any jerk / acell settings ?



  • @SputnikOC3d:

    Any noticeable increase in print times ?

    No - each print finished within 20 seconds of each other.

    @SputnikOC3d:

    Did you mod any jerk / acell settings ?

    I didn't make any changes. Here are the appropriate lines from the config:

    [[language]]
    M566 X1200 Y1200 Z1200 E1200                       ; Set maximum instantaneous speed changes (mm/min)
    M203 X18000 Y18000 Z18000 E1200                    ; Set maximum speeds (mm/min)
    M201 X1000 Y1000 Z1000 E1000                       ; Set accelerations (mm/s^2)
    
    

    Thanks,

    John


  • administrators

    How long is the Bowden tube on your printer; and what was the printing speed?

    Yor M201 acceleration settings are quite low, which means that you probably have little need for pressure advance. Pressure advance is more important when you use high printing speeds and high accelerations.



  • I also made some pressure advance tests, and didn't notice much changes as I'm also using low speed/accel. So it seems normal. I also have a long Bowden.


  • administrators

    There is a test print for calibrating pressure advance in this thread: https://www.duet3d.com/forum/thread.php?id=3661#p32897. When I get time I will put together some standard tests prints; but right now hardware and firmware development is keeping me busy.



  • I just use a cylinder about 60mm diameter single walled. Make sure its not on vase mode. Tune retraction well then add in 0.2 pressure advance print fairly fast 60-80mm/s. You'll soon see if the thin section is at the beginning of the layer (not enough advance) or the end (too much).

    It's not a perfect test but it's visually fairly easy to see.


  • administrators

    Another simple test is a single-walled cube printed in vase mode. Pressure advance affects the quality of the corners.



  • @dc42:

    How long is the Bowden tube on your printer; and what was the printing speed?

    The bowden tube is about 470mm between Titan extruder and E3D-v6.
    Print speed was was 60mm/sec with outline at 48mm/sec.

    @dc42:

    Your M201 acceleration settings are quite low, which means that you probably have little need for pressure advance. Pressure advance is more important when you use high printing speeds and high accelerations.

    I chose to start my testing at this speed as a "known" speed, and expected to ramp up from there. Because I had seen positive impact with Linear Advance at similar speeds on my MK2, I started with the same speeds here on the Delta. I'd agree that my starting position on the MK2 had worse looking corners at 60mm/sec than I do on the Delta. The process I had used on the MK2 was to try to get my 80mm/sec prints look as good as my 40mm/sec prints. I was thinking along the same lines for the Delta.

    I had also selected this model since it was closer to my "real world" prints than some of the simpler tests.

    Thanks for the insight.

    John


 

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