PA tuning Disparencies



  • Re: PA tuning
    Re: Enhancing pressure advance

    Hi,

    After countless trials with configurations, I can also confirm having similar difficulties in PA tuning and retraction tuning as other users on this forum.

    By tuning extuder jerk, retraction distance and micro stepping resolution (16x to 256x) Ive been able to make the start point from missing material to having too much material (dot) with direct drive extruder.

    The next segments are also effected - if a dot is formed, it measures 0.5mm, and the next lines measure 0.3mm, after it settles to 0.4mm after few millimeters of printing.

    Another forum user suggested dynamic unretraction constant. But using firmware from mdealer fork didn’t seem to help.

    Similar thing happens when attempting PA calibration method of Marlin PA1.5 so I tried injecting M572 D0 P0 commands to the gcode at G10 and M572 D0 P0.04 at G11. This helped in line test but not in round shape.

    Also, when using low retraction amounts, they work nicely in calibration, but in real print start randomly stringing, leaking alot when retracting and moving (when printing larger areas). Large retraction amounts make gaps. Tested with both Simplify3D code and Cura code with absolute, relative and firmware retraction modes.

    Could we make some changes to firmware where extruder or filament amount is reset at the event of retraction / unretraction?

    Other possible solution would be if the DDA would detect that this is a retraction move, and all corrections should reset when the retraction event is noticed. What would firmware developers suggest?



  • By doing more testing with Retraction distance 0.6mm and retraction speed 1800mm/min, the gaps increase if adjusting pressure advance from 0.04 to 0.07.

    Could this issue be related to extrusionPending inside dda.cpp?

    Because otherwise print quality is very good but starting point always fails by either missing material or having too much.

    Would it make sense to add anything like this to end or beginning of DDA::Prepare etc?

    if ( moveBuffer.hasPositiveExtrusion && axesMentionedExceptZ.IsNonEmpty() )
    {
    extrusionPending = 0
    }
    


  • Hi,

    @dc42 could you please comment on this?

    I was wondering if this problem could be related to other known bugs such as this one:

    Github BugList.txt: Don't do pressure advance during accel/decel of sequences of short segments [LINK]

    Could other kinematics (such as corexy vs cartesian) be more or less affected?



  • I think the Duet team is in the midst of investigating and working on improvements to PA. It might be best to hold tight and wait for the announcements. IIRC RRF 3.4 is the earliest we'll expect to see anything.



  • @petriheino said in PA tuning Disparencies:

    a dot is formed

    I've noticed the dot, too. After printing several skirt lines, it retracts and builds a dot at the landingspot.
    I blamed my Volcano hotend, because I print the first layer really slow and hot. The Volcano doesn't like that.


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