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Dual V3 start code purge sequence not purging material on E2
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The reason why E2 (T1) doesn't purge is because Marlin does not maintain current E for each extruder, only a global E value.

At the beginning of the Start Gcode, T0 and T1 are set to 0 (G92 E0) and then retracted -15 (G1 E-15 F100). (Global E is -15)

After "M117 Purging...",
T0 is moved to E0, set to E-15, and moved to E0. This works because Global E is -15 from above.
T1 is selected and moved to E0 but wait, it is already there because of the global E value being set last by T0! Marlin needs to be told that T1 is at E-15 first! Solution, add another "G92 E-15" after "T1".

The Purging section of the Start Gcode should be:

M117 Purging...              ; LCD status message
T0                           ; select this extruder first
G1  E0 F100                  ; undo retraction
G92 E-15                     ; set extruder negative amount to purge
G1  E0 F100                  ; purge XXmm of filament
T1                           ; switch to second extruder
G92 E-15                     ; set extruder negative amount to purge
G1  E0 F100                  ; undo retraction
G92 E-15                     ; set extruder negative amount to purge
G1  E0 F100                  ; purge XXmm of filament
G1 Z0.5                      ; clear bed (barely)
G1 X100 Y0 F5000             ; move above bed to shear off filament
T0                           ; switch to first extruder
M190 S{material_bed_temperature_layer_0}; get bed temping up during first layer

Event Timeline

b-morgan created this task.Mar 18 2018, 4:02 PM
alexei triaged this task as Normal priority.Jun 12 2018, 11:29 AM
alexei changed the edit policy from "Custom Policy" to "Cura LulzBot Edition (Project)".
alexei added a project: Cura LulzBot Edition.
karrad claimed this task.Jun 12 2018, 2:44 PM
karrad moved this task from Backlog to Release 3.6.xx on the Cura LulzBot Edition board.
karrad added a subscriber: karrad.

@b-morgan Thanks for the work on this one, we will get it incorporated!

karrad reassigned this task from karrad to lansky.Jun 12 2018, 2:53 PM

Please test out in TSR, and let us know what your team thinks

It still isn't fixed in 3.2.21

@b-morgan Indeed, we are testing your proposed fix internally. Once we verify it won't cause issues, we will roll it into further releases.

@karrad We ran a print with the test purge gcode incorporated. Rough measurements indicate that extruders 1 and 2 purge ~160 mm.

@johnson @lansky What are the thoughts on the change?

The amount extruded is a little much, but that is easily changeable.

Personally, I like the extrusion distance. I think it would be good especially if a previous filament was in the extruder. It would make for a more thorough purge.

@lansky @johnson I will update the distance to what you prefer, just be aware this can be a double edged sword.

Too much extrusion, will get complaints about wasting material.

Too little extrusion, complaints of skirt not priming enough.

Just let me know!

If you take into account that the end gcode retracts the filament quite a bit then the purge should be enough to actually have filament at the nozzle when you start your next print. I think I upped my personal purge value(s) to G92 E-25.

BTW, I added a purge to all of my tool heads. I don't know if you want to consider that for the default start gcode(s) or not.

karrad claimed this task.Jun 15 2018, 12:45 PM

I think the current amount is fine to implement, if users want to change it it is easily done so.

karrad closed this task as Resolved.Jun 18 2018, 8:58 AM