Extruder retraction at end of print



  • Hello,

    I've got an Ender 3 Pro running a Duet 2 Wifi with a Hemera direct drive extruder and hot end.

    A couple of days ago I played with a few things on BL touch calibration, using the BL touch for z homing for example. Nothing that I think would affect the extruder behaviour.

    Since then I'm getting a problem where at the end of my print the extruder runs backwards at full speed for a good 10 seconds. I'm asking for a relative E-2 retraction in my end G Code (copied from Cura below). I've searched the forums and google but can't seem to come up with any explanation. It does the 10 second retraction at the same time as the Z move which causes a string to form from the remaining filament in the nozzle. Can be cut off the print easily enough but it's annoying and I don't think the extruder behaviour is normal or can be good for it.

    Does anyone have any thoughts on what else might be affecting this behaviour or where I've gone wrong?

    Thanks,

    Greg

    End G Code
    G91 ;Relative positioning
    G1 E-2 Z10 ;Retract and raise Z
    G90 ;Absolute positionning

    G1 X0 Y200 ;Present print
    M106 S0 ;Turn-off fan
    M104 S0 ;Turn-off hotend
    M140 S0 ;Turn-off bed

    M84 X Y E ;Disable all steppers but Z



  • @GregL said in Extruder retraction at end of print:

    End G Code
    G91 ;Relative positioning
    G1 E-2 Z10 ;Retract and raise Z
    G90 ;Absolute positionning

    Try:
    M83 ; relative extruder moves
    G1 E-2 F3600 ; retract 2mm of filament
    G91 ;Relative positioning
    G1 Z10 F360 ;raise Z
    G90 ;Absolute positioning



  • That has fixed the extruder problem, thanks for the help!

    Not sure why it has suddenly taken issue with the previously fine G91 command to set relative extruder position but using M83 has fixed the problem.

    Still need to do a bit of tweaking on end of print retraction to fix the little bit of oozing I'm still getting but all that should be easily achieveable.

    Thanks again, Greg



  • @GregL said in Extruder retraction at end of print:

    That has fixed the extruder problem, thanks for the help!

    Not sure why it has suddenly taken issue with the previously fine G91 command to set relative extruder position but using M83 has fixed the problem.

    Still need to do a bit of tweaking on end of print retraction to fix the little bit of oozing I'm still getting but all that should be easily achieveable.

    Thanks again, Greg

    From the Wiki here https://duet3d.dozuki.com/Wiki/Gcode#Section_G91_Set_to_Relative_Positioning
    Quote....

    "Note: RepRapFirmware uses M83 to set the extruder to relative mode: extrusion is NOT set to relative using G91"


  • Moderator

    It sounds like you have Cura set to use absolute extrusion mode. Should probably change it to relative extrusion from the get go.

    Check box can be found under the "special moves" heading and may be hidden by default.



  • The reason that was happening it is was telling it to go to extruder position 2 from wherever it last was. If it is using absolute moves then that could be position 10000 or some other large number.

    Looking at the GCode that S3D generates it seems to use absolute positions but every feature or so it sends an G92 E0 which essentially resets the counter.

    Another way to do your end script would be to

    G92 E0
    G1 E-2



  • @GregL don’t forget to set it back to M82 before another print.


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