Pressure advance question

  • Hello,

    I am trying to tune pressure advance on my Bowden setup. Using just a standard 20mm cube, I can't get sharp corners even with PA set to 1.0 the corners still buldge a little. And there are little blobs where the printer changes perimeter loops. At first I thought it was a retraction issue, but with coasting set to 2mm the blob at the corner is still there. You can see where the extruder stops extruding.

    This issue is driving me up a wall, no matter what I do I can't make it better. I've even changed the jerk and acceleration settings from very high to very low, and nothing makes the corners right. There is always a little buldges and blobs.

    Does anyone have any advice that might help me?

  • Try disabling coasting as it may be interacting with presure advance. You may also need more pressure advance. How long is your tube?

  • @Phaedrux Coasting was just to check if my retraction was giving me the issue. If the blob followed the coasting, I would know I had a retraction issue to weed out. But since the blob stays at the corners, I knew it was not from a retraction issue.

    My tube is about 600mm long, I was afraid to go too high with the pressure advance since all the information and other peoples examples only go up to 0.500 max. I will try bringing up the PA later tonight.

  • After a couple hours of trying to tune PA, I noticed my speed dropped a lot. I'm requesting 60mm/s but I could only get 35mm/s. So I bumped up my jerk from 10mm to 30mm. That worked a little, but I started to skip steps. So I changed my stepper motor from a 0.9 deg 1.2A, to a 1.8 deg 2.0A motor. I have not calibrated the steps yet, and the print is looking a little better.

    I did notice something that I need a little better understanding on. With my PA set to 1.5, my extruder pulls the filament back slowly, even though I have the settings through the roof. The extruder can move filament (no hotend, just PTFE tube) at 120mm/s, and during printing, the extruder doesn't look like it is getting close to its limit. is there something I am missing? I am using a true E3D titan extruder, are the settings for the extruder what the filament sees, or what the motor sees? should my extruder values be 3x the standard value (3:1 gearing)?

    Here are my current stable settings. I still have to fine tune the extruder settings, they could go up;

    M350 X16 Y16 Z16 E16 I1 S2
    M92 X80 Y80 Z640 E418.599302 <-- still have to work on steps per mm
    M566 X1800 Y1800 Z120 E1400
    M203 X24000 Y24000 Z900 E9600 <-- printer can travel at 400mm/s
    M201 X3000 Y3000 Z75 E3000
    M204 P500 T3000
    M906 X1600 Y1600 Z1300 E1500 I20
    M84 S30

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