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Extra Retraction at Start


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Posted (edited) · Extra Retraction at Start

@GregValiant 

G92 E0 ;Reset Extruder
G1 Z2.0 F3000 ;Move Z Axis up
G92 E0
G92 E0
G1 F1800 E-5           <----Here.
;LAYER_COUNT:171
;LAYER:0
M107
G1 F300 Z0.4  <---- picks up nozzle?

 

In the previous code snippets, it is there too.  The amount varies I think based on the retraction settings you have stored.

 

Update:  So I made a noob mistake (yes, I've only had the printer a short while).  It was the z-offset that was really causing the problem for my first layer.  However, the above extrusion is still interesting, although not critical anymore.

Edited by KronosMT
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    • 5 weeks later...
    Posted · Extra Retraction at Start

    i am also trying to remove/modify the retract line right before starting the first line being printed.

     

    G92 E0 ;Reset Extruder
    G1 Z2.0 F3000 ;Move Z Axis up
    G92 E0
    G92 E0
    G1 F1800 E-5           <----Here.
    ;LAYER_COUNT:171
    ;LAYER:0

     

    i have an ender 3 v2 and cannot pick 2 extruders from the drop down in machine settings, as others say.

     

    has anyone been able to either modify the json file or find a way to edit the applicable cura nozzle settings in a backdoor manner?

     

    search and replace is not a good option, as i modify the retraction and feed rate frequently depending on what im printing...

     

    thanks for any help!!

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    • 2 weeks later...
    Posted · Extra Retraction at Start

    I'm also having the same issue as everyone else. Extra retraction and E0 command between Start code and print code. It seams to be related to the retraction settings in the profile menu! With retraction enabled it's automatically adding the extra code with the retraction amount matching what ever youv'e set in the profile. Doesn't matter what printer you have as I've loaded several with there default settings in tact and its always the same in the code and writes this extra line that matches those settings. It's a real pain as it means the print doesn't start till that retraction is made up via normal print extraction distance, it then dribbles out and F£$s up the print. Below is a code example same as everyone else's. ATM I'm just deleting this line of code manually from the file in a text editor (notebook!) but that's a bit of a pain!

    So any other suggestions people?

     

    G1 X30 E15.4704 F1200 ;continue purge lines back to start
    G1 Z-0.1 X150 F5000 ;wipe nozzle
    G92 E0 ;Zero extruder
    G92 E0
    G92 E0
    G1 F4200 E-6.5 =======These are the extra line of code!

    ;LAYER_COUNT:33
    ;LAYER:0
    M107
    G0 F2880 X92.552 Y96.245 Z0.32 ;adjusted by z offset
    G92 Z0.3 ;consider this the original z before offset
    ;TYPE:SKIRT
    G1 F4200 E0 Here it zero's the extruder but the fillament is still 6.5 mm up the tube!!!!!!!!
    G1 F1200 X92.998 Y95.921 E0.0275
    G1 X93.486 Y95.666 E0.05497

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    Posted (edited) · Extra Retraction at Start

    I agree this delays the start of any extrusion at the beginning of a print.  I don't like it.  Most people don't notice it as it only affects the skirt or brim.  The "Start G-code" of some printers includes thick and heavy purge lines that mitigate this.

     

    @Marky, the final line you have highlighted is a G1 line, not a G92 line.  It advances the filament from -6.5 to 0 at 4200mm/min.  So the filament does indeed end up at the nozzle.  I believe the initial under-extrusion is due to oozing rather than the numbers in the Gcode and although it looks like it should work (the numbers do add up), there is no pressure at the nozzle and so extrusion doesn't start immediately.  In my case that is for anywhere from 30 to 120mm.  For parts with a maximum build plate footprint (that I can't use a skirt/brim on) this delays the extrusion of the first layer of the actual part.  It also can end up with the nozzle dragging around a "string of beads" that ends up in the area of the print.

     

    The Search and Replace workaround (that I described earlier) works.  In Marky's example it would SET the extruder to -6.5 with the filament still at the nozzle ready to extrude.  When the later G1 F4200 E0 line advances the filament - there is a serious prime which will sometimes leave a blob.  If I could measure the amount of oozing (which ain't happenin' because it's temperature and time dependent) that blob could be adjusted to nothing and extrusion would start as we expect.

     

    One fix for this would require the addition of a setting to the Travel section.  "Initial Print Prime" (new keyword {retraction_print_prime}??) that would effect that single line in the Gcode.  Instead of "G1 F{retraction_retract_speed} E-{retraction_amount}" it would be "G92 E-{retraction_print_prime}.  That would leave the filament at the nozzle, but set the extruder location back.  A few lines later the filament advances to 0 as it does now, but the filament starts at the nozzle, not retracted, so it results in immediate extrusion start which is what we want.

     

    A second fix is to add "purge lines" to the Start G-Code of your printer.  MaxX size prints require a snatch-and-grab to get rid of the purge lines before they become part of the print but that doesn't happen often.

    Edited by GregValiant
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