Mysterious retraction:



  • Hi,

    I have a tool changer running a prime.g script after picking up a tool.
    Prime.g is supposed to brush over the nozzle, purge the nozzle with filament, brush again and start printing.
    What I find is happening, that after the purge I'd like to have 3mm retraction, but I get approx. 10mm (10second long, not sure how much). Does anyone see where it comes from?

    purge.g:

    ;brush in
    G1 X-23 Y171 F25000
    G1 X-23 Y207 F25000
    G1 X-23 Y171 F25000
    G1 X-23 Y207 F25000
    
    ;Park for prime/purge
    G1 X-23 Y223 F50000
    
    ;Prime
    G92 E0
    G1 E50 F200 ;extrude 50mm
    
    ; HERE: approx. 10s of slow retraction. Why?
    
    G1 E-3 F200 ;retract 3mm
    G92 E0
    
    ;Run Out
    G1 X-23 Y207 F50000
    
    ;Brush Out
    G1 X-23 Y205 F25000
    G1 X-21 Y200 F25000
    G1 X-23 Y195 F25000
    G1 X-21 Y190 F25000
    G1 X-23 Y185 F25000
    G1 X-21 Y180 F25000
    G1 X-23 Y175 F25000
    G1 X-21 Y170 F25000
    
    G1 X-23 Y170 F25000
    G1 X-23 Y205 F25000
    ;brush in
    G1 X-23 Y171 F25000
    G1 X-23 Y207 F25000
    G1 X-23 Y171 F25000
    G1 X-23 Y207 F25000
    


  • Hi,

    Is the extruder set to Absolute or Relative mode?

    Frederick



  • Using PrusaSlicer, "use relative E distances" is unchecked. So I guess absolute?



  • @schmluka said in Mysterious retraction::

    Using PrusaSlicer, "use relative E distances" is unchecked. So I guess absolute?

    Check it and try again.

    Frederick



  • is there any other work-around? I always thought you are supposed to use absolute extrusion values for higher precision?



  • @schmluka said in Mysterious retraction::

    is there any other work-around? I always thought you are supposed to use absolute extrusion values for higher precision?

    I was always told to use relative.


    Link to article talking about Relative or Absolute


    With relative you retract with negative values - G1 E-3.

    But with absolute to retract 3mm after a G1 E50 you would use a G1 E47.

    Frederick


  • Moderator

    @schmluka said in Mysterious retraction::

    is there any other work-around? I always thought you are supposed to use absolute extrusion values for higher precision?

    The firmware has to convert to relative extruder values anyway. Absolute is a holdover from the early days of reprap and can be safely left behind.



  • @fcwilt Thanks for the quick help. Changing to relative E distance worked.


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