TAZ6 Dual Extruder v2 extrudes a bunch of excess filament before starting print

I have been running my TAZ6 for a couple of months and just put on the Dual Extruder Head v2 today. I’m printing out the calibration squares, and having a couple of strange issues.

(1) It was retracting far too much. At one point, one of the extruders retracted so much that it expelled the filament out the top and I had to reload it. I managed to fix this issue by going into Cura and changing Retraction > Dual extrusion switch amount from 30mm to 10mm. I don’t know why this was set so high initially?!? I certainly didn’t change it. I mention this just in case it is related to my current problem:

(2) Right after auto-leveling and just before beginning the print, it spits out a bunch of junk filament. First, the primary (T0) tool head extrudes a bunch of filament. Then the secondary (T1) tool head extrudes a bunch of filament. By a bunch, I mean like on the order of 60-80mm - almost enough to form a life-size hershey’s kiss ABS booger. If I pause the print and remove this, it completes the print OK.

Any advice on booger prevention?

Probably something to do in the start script.

Look for a line after a T0 (after the wipe process) that looks like “G1 Exxx”… could have a Fnnn.

Here is the code from start2.gcode that follows the wipe process:

G1 Z10                       ; raise extruder
M109 S170                    ; heat to probe temp
G1 X-9 Y-9                   ; move above first probe point
M204 S100                    ; set accel for probing
G29                          ; probe sequence (for auto-leveling)
M204 S500                    ; set accel back to normal
G1 X0 Y0 Z15 F5000           ; get out the way
M400                         ; clear buffer
M140 S{print_bed_temperature}; get bed heating up
M104 S{print_temperature} T0 ; set extruder temp
M104 S{print_temperature2} T1; set extruder temp
M109 S{print_temperature} T0 ; set extruder temp and wait
M109 S{print_temperature2} T1; set extruder temp and wait
T1                           ; switch to second extruder
G1 E0 F100                   ; prime nozzle from previous print
G1 F100 E-{retraction_dual_amount} ;retract second nozzle before print
G92 E-30                     ; adjust to 1st nozzle e value
T0                           ; switch back to back
M190 S{print_bed_temperature}; get bed temping up during first layer
G1 Z2 E0 F75                 ; extrude filament back into nozzle
M117 TAZ Printing...         ; LCD status message

I am new to gcode, so is it the line

G1 E0 F100

that causes the problem? Does this indicate extrusion of 100mm of filament? I am unsure as how to modify it.

No, that says to Extrude to 0 mm at Feed rate 100 MM speed. You probably retracted some filament earlier in the start scripts.

Also if you change the amount you feed it from 30 MM you will need to change the amounts to feed and retract in the start script also, as they are hard coded to 30 MM. (The line 2 below the one you asked about with the E-30.)

OK, I don’t think I trust myself enough to start fiddling with the gcode … I will likely hose it all up. I called Lulzbot support and they suggested I make a video of this, so here it is:
https://www.dropbox.com/sh/qgm17ihx9wpzgr5/AAAG3AWr2HiBks-Ib4ne__Bla?dl=0

There is nothing to see after the first 50sec or so - I just kept waiting to see if the other one would also extrude. When it also does this weird extrusion thing, T0 (the back one) always goes AFTER the front one (T1).

If you are going to use a dual extruder and expect it to perform as well as the single extruder setup, you are going to have to learn gcode, or find a friend who knows it. It’s not very hard to learn. The default start/end scripts for the dual extruders leave a lot to be desired. The whole dual extruder thing from Lulzbot leaves a lot to be desired. The end script retracts too far after the print is complete. The start script doesn’t clean thoroughly enough. The cleaning pad should be modified so the front extruder doesn’t touch anything during the cleaning process. I could go on and on. IMO the product development is not yet complete on the dual extruders, however if you take the time to set them up properly (i.e. do the post engineering and development) they do perform good. At least they are available for purchase even if they require some post user development. BTW if you make the switch to Simplify3D for dual extrusion, the need to know gcode is even more important. IMO Simplify3D is not simple (not even close), it’s much more complicated than Cura, however it has some nice features for dual extrusion. I must throw caution though, some of the features in Simplify3D do not play nice together, meaning it has so many features that if you enable the wrong thing, you will get unexpected results, which is why I recommend that you go ahead and learn gcode. It will probably help you out (at least in the near future) if you plan to use a dual extruder. As 3D printing software matures the issues we currently face will likely fade away.

A reference for gcode RepRap if you have not come across it already.
http://reprap.org/wiki/G-code

Thanks for the tips, everyone. I called Lulzbot support and they were quite helpful. I upgraded to Cura v20, and this seems to have done the trick - no more weird behavior.