Nozzle stops at perimeter change



  • Hi folks,
    As I'm currently analyzing my blobbing problem, I noticed the following:
    When retracting at layer change, the nozzle pushed quite a big blob at the start or the first (inner) perimeter.
    Additionally, the nozzle stops for a split second when it changes to the next perimeter(s) which also results in additional blobbing.
    Does anyone have a clue why this stopping occurs?
    Link to S3D profile and Duet config:
    https://drive.google.com/drive/folders/1Km_6ZQwyBDyLP2Ud__PldtW7bxEX-NcE?fbclid=IwAR3nCLb5PsGNBp8A_SwU41jG-jFciY0TJX-w4Bt0CYU6mMRsYJOXp-UB6xk

    Thanks in advance,
    Paul


  • Moderator

    It looks like you're retracting 12mm of filament at 10mm/s which is going to cause a noticeable pause on layer change. At least that's what I gathered from the factory file plain text since I don't have S3D. But the behaviour you describe would be consistent with slow retraction or slow layer change.

    I suggest tuning your retraction to see if you really need 12mm and increasing the retraction speed.



  • I'm retracting 6 or 6.5mm at 60mm/s.
    Dont know where these numbers come from 🙂

    Update:
    The short stop is also present on an object sliced with Slic3r.


  • Moderator

    Are you using coasting or wipe on retract?
    Pressure advance?
    Firmware version?



  • @phaedrux
    No wipe or coast is used (wipe + coast gave me worse results).
    PA is disabled, Firmware version 1.21


  • administrators

    It will be easier for us to work out what is going wrong if you share a GCode file that exhibits the symptom.



  • @dc42
    Good idea.
    Gcode file added to the Google Drive link from above


  • administrators

    @royce said in Nozzle stops at perimeter change:

    Additionally, the nozzle stops for a split second when it changes to the next perimeter(s) which also results in additional blobbing.
    Does anyone have a clue why this stopping occurs?

    Retracting 6.5mm of filament with speed 60mm/sec and acceleration/deceleration 2000mm/sec^2 will take 0.14sec. So will re-priming. Is this the "split second" that you observe?



  • Well, when changing perimeter lanes (from inner to mid to outer), there is no retraction. It just changes the lanes.
    So I dont think the stop has something to so with the retraction.


  • administrators

    I'm sorry, I misunderstood. Here is a sample perimeter change from your file:

    G1 X168.762 Y144.337 E0.0357
    ; feature outer perimeter
    G1 X169.050 Y143.953 F7200
    G1 X169.534 Y144.346 E0.0231 F1800

    It should complete the last extrusion of the inner perimeter (coming to a stop at the end of the move), execute the ~0.5mm travel move, then start the new perimeter. The time it takes to do all that will depend on your acceleration settings. If you are using a Bowden extruder and no pressure advance, then there will be some over-extrusion at the end of the inner perimeter, some oozing during the short travel move, and perhaps a little under-extrusion at the start of the outer perimeter. The fix for that is to use pressure advance.



  • That's good to know.
    So I need to dig into the PA feature a little more, I didnt use it so far.
    Any point to start?


  • administrators

    For a non-Bowden extruder, try 0.05. For a Bowden extruder, try 0.2. For best results, search this forum for threads on calibrating pressure advance.



  • Thank you, I'll read it up 🙂
    Very much appreciated!



  • @dc42
    Do I need to set M572 in the config or in the slicer's start code?


  • administrators

    It doesn't matter. I set it in config.g. If you find that you get best results using different values for different filaments, you can put it in the slicer start GCode instead.

    You can change it on-the-fly by sending the M572 D0 Snn command from the GCode Console of DWC, or over USB, or from PanelDue. It takes a few seconds for the new value to take effect.

    Note, if you use high values of pressure advance (e.g. above 0.4) then you may need to reduce retraction, to avoid over-retraction.


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