PETG problems - finally solved. Pressure Advance M572 values in filament custom GCode need updating for Obxidian nozzles...  

PETG problems - finally solved. Pressure Advance M572 values in filament custom GCode need updating for Obxidian nozzles...

I feel as though I have reached the end of a particularly frustrating tunnel, and I have found that the light is not actually a train.

I have an XL 5-tool, currently with two 0.4mm Obxidian 500 high-flow nozzles, two 0.4mm Obxidian high-flow nozzles, and a 0.6mm Obxidian high-flow nozzle. I have a general preference for printing with PETG, and I'm hoping to play with the UltraGlow and PC-CF filaments as well.

I had been having significant problems with all varieties of PETG filament buildup around nozzles, that buildup causing printhead crashes with prints, buildup dropping onto prints and creating a raft of weird problems both structural and aesthetic, problems with gaps in layers where filament extrusion wasn't "gripping" to the underlying and adjacent print layers, and a significant amount of time and effort and filament reels being wasted in pursuit of "good enough".

I had tried all of the advice, from manipulation of the temperature of extrusion, significantly lowering the feedrate of filament, significantly lowering the printhead speeds, changing the fill types to avoid crossing, varying the extrusion percentage, lots of playing with retraction and wipe and Z-move settings. Nothing was giving me similar results to what I had been getting when I first assembled the printer, and everything was having similar problems. Reverting firmware didn't help either.

As it turns out, one of the few configuration items I did not play with was the "Pressure Advance" parameter, that is in the M572 GCode setting.

Following the suggestions here: https://www.printables.com/model/641490-prusa-slicer-pressure-advance-test I set up the test print with a range of parameter from 0.01 through 0.30 in a couple of prints. For my setup, the HF500 nozzles were looking best with M572 values in the 0.08 to 0.09 range, and looking noticeably poor in the 0.05-0.06 range, and from 0.12 upwards. This was using dried Prusament PETG in the SignalWhite flavour.

Checking the "Custom GCode" for the filament profile, I had seen that in the code there, if the nozzle was advertised as 0.04mm, that the value for Pressure Advance was being set at 0.53.

Setting that value in the custom code section to 0.09, and running a print through one of the normal slightly-modified print profiles that I had previously been having lots of trouble with, I ended up with a print that completed without blobs, that had a consistent surface finish, and that had a nozzle that was free of filament. I was really surprised at the difference this made..

Changing the parameter for other PETG filaments that had poor results previously, allowed similar high standards of completed test prints. 

I effectively have a printer that (assuming no bed adhesion issues, but that is another story!) is pretty much guaranteed to give me a print output that is what is expected, and without the problems that were present.

I am _happy_ now.