Pressure Advance: Doesn't Behave as Expected

In doing some manual pressure advance calibration, using the scripts built into Orca Slicer, I found some strange behavior.

While the test starts out as you would expect, with some under-extrusion at the beginning of the fast print move, and over-extrusion at the end (not enough PA); as you move through “ideal” PA and into “too much” PA, the behavior is not good.

Rather than seeing the over-extrusion and under-extrusion switch positions on the print line, we see a return to the “under PA” behavior, but worse.

To me, it is looking like the extruder is skipping steps:

Material: Bambu PLA
Speed: 20 - 180 mm/s
Accel: 8000 mm/s2
Layer height: 0.2 mm
Line width: 0.6 mm
PA Range: 0.010 - 0.030

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0,020 seem the best.

That’s somewhat beside the point. Even 0.020 doesn’t look very good.

Every one of these lines shows underextrusion at the start of the fast segment, which shows that PA isn’t working well.

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