Tool Change retraction confusion

marzubus

I am having a bit of a hard time understanding something that should be simple. I have a pebble wiper, that purges a pellet and whacks it with a servo after every tool grab. After the pebble is formed, I retract 4.8mm, before print resumes.

; prime.g
G92 E0                    ; Reset Extrusion
G1 E-4.8 F1500      ; Retract

In my slicer settings, I am confused as to if the unretract will undo this retracted state, as in generated gcode, it looks like there is an additional retract after my tool is grabbed, and it undoes that retract obviously, but does the printer know about and undo the other 4.8mm retraction too?

; slicer code
; tool change
T1
G1 E-4.8 F2400
G1 X137.29 Y76.988 F21000
G1 Z.2
G1 E4.8 F2400

I am confused as to if the printer knows about that extra retract in prime.g, and does it undo that when extrusion starts again?

Does the G1 E commands undo the extra retraction I have in my prime.g?
Do I use postX.g scripts retract 4.8mm or do I use PrusaSlicer per tool retraction when stowing tools? Does this make any difference? As I like to use PrusaSlicer's wipe and retract.
When I grab a tool, I unretract, purge, then retract to stop drooling, but the first time any tool is used, it seems to not be unretracting the right amount before first line. So there is a initial underextrusion.

dc42

@marzubus the printer firmware only knows about retraction if you configure your slicer to use firmware retraction (G10 and G11 commands) and configure the amounts of retraction and reprime using M208. If you do not use firmware retraction then it is your slicer that is in control of retraction, apart from any manual retract and reprime commands that you use, for example in tool change files or pause.g and resume.g.

It may be that your slicer retracts filament from the old tool before doing a tool change, and primes the new tool after a tool change.

If you use firmware retraction then RRF tracks the retraction state and will ignore a G10 command if the filament is already retracted by a previous G10, or a G11 command if the filament is not retracted.

marzubus

@dc42 Does that mean I can use G10 and G11 in the script g-codes, while the job uses normal G1 E extrusion?

dc42

@marzubus you could, but I don't see how that would help.

marzubus

@dc42 I think I am just over thinking this, if I use G1 R2 I can zip back to the print position rapidly with only minor retraction.

prime.g

G91                   ; relative pos
G1 Z3 F1000           ; raise Z
G90                   ; back to absolute pos

M106 S0               ; fan off
M109                  ; wait for temp
M42 P0 S1             ; turn servo on
M280 P0 S100          ; servo home 100 degrees
G4 P100               ; wait 1 second

; move near pebble wiper, two movements to come in from 
; the right edge so any tail hangs over the far edge.
G0 X-35 Y160 F30000
G0 X-42 Y161 F24000
G0 X-39 Y153 F24000   ; move to pebble wiper purge spot

; make a pebble
G1 E1.5 F200          ; purge reduce from 5 to 3
G4 P200               ; wait 200ms
G1 E5 F300
G4 P200               ; wait 400ms; 
G1 E10 F500           ; purge
G1 E5 F360            ; Pebble Purge
M106 S1               ; fan 100%, cool and harden the pebble
G1 E1 F240            ; Final Slow Pebble Purge
G4 P14000             ; Dwell for 12s, a bit long, need to tune down this.

; do a minor retraction
G92 E0                ; reset extrusion
G1 E-0.4 F1500        ; Retract a bit

; servo wack the pebble away
M280 P0 S0            ; whack!
G4 P250               ; Dwell for milliseconds

; zip over the brush
G0 X-35 Y123 F24000   ; move across brush
G0 X-39 Y200 F24000   ; back over the brush
G0 X-35 Y123 F24000   ; move across brush
G0 X-39 Y200 F24000   ; back over the brush
G0 X-35 Y200 F24000   ; back over the brush
G0 X-25 Y131 F24000   ; back over the brush
G0 X-40 Y131 F24000   ; back over the brush
G0 X-25 Y131 F24000   ; back over the brush


M106 R2               ; Cooling Fan Off
M280 P0 S100          ; servo home                 
M42 P0 S0             ; servo off

; restore Z before moving tool back
G91                   ; relative pos
G1 Z-3 F1000          ; lower nozzle
G90                   ; back to absolute pos
G29 S1                ; mesh levelling on

; return to position where toolchange was initiated from
G1 R2 X0 Y0 Z2 F50000 ; Move to saved position at lightning speed
G1 E0.4 F1500         ; Unretract
G92 E0                ; reset extrusion