Deretraction - when is it executed by the firmware, does the printer MOVE ON to the next line before it is completed?
 
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Deretraction - when is it executed by the firmware, does the printer MOVE ON to the next line before it is completed?  

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kevin1954
(@kevin1954)
Active Member
Deretraction - when is it executed by the firmware, does the printer MOVE ON to the next line before it is completed?

PETG in Prusa Slicer 2.3.3

I had an under extrusion (for 2-5 mm), immediately AFTER a "long move" retraction.

It was TOTALLY solved by speed increase of the Deretraction.

Now I wonder "why"?

The Deretraction gcode section follows...
The question is, does the printer/firmware "complete the Deretraction move", BEFORE beginning the extruding move of the LAST line below?  And if so, WHY did a FASTER DERETRACTION SPEED "absolutely" fix the under extrusion which was occuring at the location, at the start of the LAST line?

GCODE snippit follows...
G1 Z1.000 F7800.000  ;Z retract
G1 X149.009 Y96.593  ;Move to new location (no extrusion)
G1 Z0.800  ;Z lower to printing layer
G1 E0.70000 F3000.000  ;Deretraction with speed of 50 ms
M204 S800  
G1 F1500.000  ;Set feed rate for normal processing
G1 X149.009 Y95.891 E0.71828  ;;  !The extruding move, this is where it UNDER EXTRUDES for 2-5 mm occurs UNLESS I set Deretraction Speed from 35ms to 50 ms

FYI: Retraction Speed is 35ms, NOW Deretraction speed is 50ms and it ABSOLUTELY fixe the under extrusion issue?

I tried the best I could to explain, hope it somehow makes sense.

Thanks for all your help!

 

Posted : 08/12/2021 12:56 pm
Neophyl
(@neophyl)
Famed Member
RE: Deretraction - when is it executed by the firmware, does the printer MOVE ON to the next line before it is completed?

You are asking a question about firmware in a prusa slicer forum.  Its entirely dependant on the firmware how it handles gcode passed to it.  Ask that question to the people who wrote your printers firmware.

Regardless of the firmware, detract speed has effects on material flow too.  Its physics.  By retracting filament you are creating negative pressure in the molten plastic in your hotend.  Different retraction speeds are going to effect the plastic in different ways.  As an example to visualise, a slow pull on a length of rope causes it to move back a small amount, a sharp pull of the same distance will cause it to whiplash and move further.  That's just one effect.  Remember that even non flexible plastics like pla are 'still' flexible to a certain extent too.

When detracting it has to fill that space back up and the same sort of elasticity of filament has to be done in reverse.  Then theres backlash to consider.  While there shouldnt be any backlash ideally, its a mechanical system and real world doesnt often meet theoretical ideal. Thats why theres other settings like extra length on restart.  All to try and tune the extruder output.

Just be glad you were able to figure out a tuning setup thats working for you.

Posted : 08/12/2021 1:46 pm
kevin1954
(@kevin1954)
Active Member
Topic starter answered:
RE: Deretraction - when is it executed by the firmware, does the printer MOVE ON to the next line before it is completed?

Great explanation!

Yes, I am VERY happy to definitively fix and issue which was so serious, "on my particular parts".

Thanks for the feed back!

 

Posted : 08/12/2021 2:12 pm
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