Delay extruder to improve blobs and zits

  • Hello everybody,
    Please excuse following my english but google tries his bestets.

    To my problem .....
    I have small blobs with the slicer (S3D) are not get away.
    This is not due to the settings of the Slicers.
    The extruder is operated with the standard driver of the Duet Ethernet.
    The axes X, Y & Z are operated via external drivers.
    My guess:
    The signals to the external drivers are delayed;
    X, Y, Z
    step timing microseconds

    not to the extruders;
    step timing 0.0,0,0,0,0,0,0 microseconds

    Thus, in the outline of the start of the axis to the extruder is not synchronous and the axis starts delayed with the extruder starts immediately.

    Is it now possible to increase the times of the extruder to achieve a delay?

    Please kruze info if this way of thinking is right or there are other ways to synchronize / delay.

    Best regards


  • administrators

    @visioneer I am not sure that the issue is the 3 microseconds difference in step timing, especially as the internal drivers have a 2 microsecond timing by default (from memory). Have you looked at pressure advance as part of the solution?

  • If the extruder started moving before the axes, then this would result in blob at the start of a move, which is really unusual given that most blob are formed at the end of moves. Are you sure that this is the case?

    Given the nature of how hot viscous filament acts, I'd doubt very much if a 3 micro second delay on the extruder would have any noticeable effect. My maths might shaky here but if you take say 400 steps per mm for the extruder and run it at say 5mm/sec, then that's 2,000 micro steps per second. So a delay of 3 microseconds would equate to a lag of something like 3/500 of a microstep (but I might well have got the maths wrong on that).

  • The drain is in the outline as follows ....
    When changing to the outer line is at the beginning of a minimal
    over extrusion. At the end, parameter: M572 D0: 1: 2 S0.06
    so that a clean spout is guaranteed.
    The values of the X and Y axes are in the Acceleration and Jerk ranges
    M201 X1050 Y1050 Z200 E2000
    M566 X2100 Y2100 Z10 E1000
    I definitely have a problem that the extruder runs minimally in advance.
    I do not doubt that the temperature is a bit too high. But this is due to the strength of the component.0_1539166133175_P1060945.JPG

    I made a high-resolution image in which I marked some places

    Is there a way to delay the extruder when switching to the outer line?

    Thanks for your help

    Best regards


  • That's simply ooze from the previous move leaving a blob, not the extruder starting too early. Try more or faster retraction and / or increase pressure advance.

  • Supplement to the steps .....

    M92 X1009,000 Y1010,000 Z201,000 E2075,000

    Matematically there would be a little delay.


  • When changing from the penultimate outer line to the outer line no retract takes place.

  • @visioneer said in Delay extruder to improve blobs and zits:

    When changing from the penultimate outer line to the outer line no retract takes place.

    Try increasing pressure advance then. Or print slower. Or try a lower temperature. Or look at your slicer settings to see if there is something in there that is disabling retraction for those moves.

    The problem is definitely that when you stop the extruder motor, filament continues to ooze out of the nozzle - especially in situations where there is no retraction to pull it back. So pressure advance will help. Also printing slower will reduce the nozzle pressure. A lower temperature will make the filament more viscous (less runny). A high instantaneous speed change (jerk) and or higher acceleration will reduce the time that it takes te print head to move from one perimeter to the other. Any or all of these things might help.

  • administrators

    Using the T parameter doesn't delay the start of the step pulse unless there the last one ended less than 3.2us ago, or the direction signal changed value less than 5.3us ago. Also I am sure that a delay of 3us won't cause a noticeable effect. But there is nothing to stop you using the same T parameter in the M569 commands for the internal drivers too.

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