Retract inactive nozzle before starting print

[b-morgan]

I'm printing on a LulzBot TAZ6 with a Dual Extruder V3. I have PLA in the first extruder and PVA in the second. The retract distance for T0 is 1mm and the retract distance for T1 is 5mm.

Looking at the GCode produced from S3D after the start GCode. The first code block below (comments with ;; added) appears to assume that T0 is the selected tool (and it is). The second code block is before the first use of T1 and it appears to assume that T1 still has filament at the nozzle tip (which it does, what's left anyway). The third code block is before the switch back to T0 and shows T1 being retracted and T0 being un-retracted (primed). The fourth code block shows the same before the next switch back to T1.

My problem is that T0 and T1 are both primed and T1 with PVA really likes to ooze. The skirt starts printing and PVA blobs appear every time T1 crosses over the filament laid down by T0.

After a couple of tool changes, the inactive nozzle is retracted and the newly active nozzle is primed and for the most part, printing proceeds normally.

What I want to happen is that S3D retracts the inactive nozzle before starting the skirt. I believe it will then remember that it is retracted and generate the proper GCode to prime it before using it. Is there something I can do to make this happen?

I don't believe editing the GCode manually will work because S3D doesn't know where each nozzle is.

Code: Select all

	;; start of generated GCode
G92 E0
G1 E-1.0000 F1800	;; retract distance for T0
G1 Z0.600 F1000
; process Process1
; layer 1, Z = 0.400
T0
; tool H0.400 W0.650
; skirt
G1 X121.572 Y89.083 F4800
G1 Z0.400 F1000
G1 E0.0000 F540		;; un-retract the above
G92 E0

Code: Select all

	;; first use of T1
G92 E0
G1 E-12.0000 F600	;; retract T0 before tool change
G1 Z0.600 F1000
T1
; tool H0.400 W0.500
; prime pillar
G1 X103.387 Y204.934 F4800
G1 Z0.400 F1000
G92 E0

Code: Select all

	;; second use of T0
G92 E0
G1 E-12.0000 F600	;; retract T1 before tool change
G1 Z0.600 F1000
T0
; tool H0.400 W0.650
G1 X133.937 Y198.102 F4800
G1 Z0.400 F1000
G1 E-0.5000 F600		;; un-retract T0
G92 E0

Code: Select all

	;; second use of T1
G92 E0
G1 E-12.0000 F600	;; retract T0 before tool change
G1 Z0.600 F1000
T1
; tool H0.400 W0.650
G1 X101.887 Y204.166 F4800
G1 Z0.400 F1000
G1 E-0.5000 F600		;; un-retract T1
G92 E0

[b-morgan]

Using a Tool Change Script almost solves this problem but there are some shortcomings in that approach as well. I have started another topic for that.