Strange behaviour at the end of a print



  • So after building a Prusa i2, failing to get anything out of the hot-end, shelving it for years and finally coming back to it with a new hot-end (Pictures below - Please excuse the extruder being held on by a cut-up Ferrero Rocher box and the Duet Wifi floating in the air) - I've finally printed something !

    The print came out okay at the start, but sadly melted due to my lack of print cooling fan, that's an easy fix however.

    One thing I did notice was some strange behaviour at the end of the print. When it got to the last position, the print head stopped, the heaters were turned off and then it seemed to just sit there - A little while later I noticed that the extruder was retracting a lot, enough to empty my bowden tube and then some.

    While wondering what was going on, I ticked the "Pause at end of print" so I don't know if this messed up the numbers, but the UI at the end says "Extruder Drives: Drive 1: -2". The G-Code (From Cura) is lined below, but it looks like the last retraction part didn't go into relative mode or something like that ? After it finished its retraction, it then moved the head out of the way as expected.

    Any ideas as to what caused this ? I have E1 set as a second Z axis driver:

    M584 X0 Y1 Z2:4 E3
    
    

    https://objects-us-west-1.dream.io/yngndrw/PI_xyzCalibration_cube.gcode

    https://objects-us-west-1.dream.io/yngndrw/3D%20Printer/3D%20Printer%20-%20Overview.jpg
    https://objects-us-west-1.dream.io/yngndrw/3D%20Printer/3D%20Printer%20-%20X%20Carriage.jpg
    https://objects-us-west-1.dream.io/yngndrw/3D%20Printer/3D%20Printer%20-%20Hot%20End.jpg


  • administrators

    That behaviour is usually caused by a combination of two things:

    1. Your slicer is generating absolute extruder coordinates. We recommend you switch it to relative extruder coordinates. Cure is the only slicer that doesn't support them.

    2. You have a command in your slicer end gcode to retract a little filament, and that command uses a relative extruder command, but it has no M83 command before it.



  • Thank you David, I didn't realise there were separate machine / extruder commands for absolute / relative positioning.

    I'll switch over to relative extrusion when Cura starts supporting it and in the meantime I'll litter the header and footer G-Code with M83 / M82 where required.

    Thanks.


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