I have a Pro with a dual extruder. Printing with 2 colors of Polymaker PETG using Cura. Cura and the printer firmware are up to date and the printer is calibrated. I’ve had this printer for years and it just started doing this about a month ago.
Extruder 1 starts the print fine. When the machine switches to extruder 2, it doesn’t extrude for the first several layers. The feed gears are moving, and the filament is not stripped.
If I back the tension off and manually insert filament, it feeds right away, but like it is clogged. This light feeding seems to last for several layers and then prints fine.
I do not know what to do. It seems like extruder 2 is retracting the filament too far. The second color doesn’t even come out for at least 2 layers. Even with the manual insertion of the filament, the first layers after the color change are thin (see picture).
IIRC, Cura does a lengthy retract on the filament when it switches toolheads. This retraction in extruder #2 isn’t properly de-retracted at the end of a print, so if you have extruder 1 in red, extruder 2 in green, it:
Prints in red, retracts the red 20mm.
Switches to green. Prints in green, retracts green 20mm.
Switches to red. Un-retracts the 20mm, then prints.
Print ends.
At this point, green is still -20mm from the nozzle tip, so until 20mm worth of green has been extruded according to GCODE, there’s nothing to come out.
This would be bad enough, but now, when the nozzle heats up, there’s only remnants of filament inside. As the nozzle is heating it’s at 100% power, and parts of it are going to exceed the optimal filament temperature and can get burnt (the same reason you don’t put food in an oven that’s pre-heating). The overcooked filament is not going to flow the same, and can easily clog a nozzle, or at least interfere with flow as it gets worked through the nozzle.
Older Dual startup gcode had a fairly lengthy purge before a print that accounted for the final retraction of the toolhead, but I have been using a custom OrcaSlicer profile for my Dual that (IMO) handles things better. I haven’t started modifying my Pro yet, so that profile should be good for all stock Taz Pro Duals. If you want to give it a try, I’ll post that profile.
I had that retraction length problem last year & this is what solved it according to lulzbot
But good news I have another toolhead for 1.75 but I was also told I can make special requests for 1.75
