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NAB 🇬🇧🇪🇺🔶:marmite:

Calling all people - HELP! I can't for the life of me work out why PETG is doing this (PLA prints perfectly) - it's the 2nd infill layer that seems to be doing this. I've tried increasing temperatures. I've tried slowing the print down. I've tried increasing extrusion. This happens for all PETG filaments (the only common factor is that they're a couple of years old). This is the best quality I can come up with. Does anybody have any idea what the cause is or what else I could try?

Thank you to those who've suggested moist filament. I shall dry it and try again.

So... the answer is two-fold. Firstly there was moisture in the filament which overnight in a dehydrator sorted out, but the second is that while I can print PLA at 250mm/s, PETG simply won't. Drop it to 125mm/s and it prints fine.
Ho hum.

@NAB PETG is very prone to moisture absorption issues, which fits with its age. Might be worth drying your spool and trying again?

@tamonten Thank you. I did wonder about this, but thought that since it was stored next to the PLA that prints fine, it would be OK. I shall shove it in the dehydrator!

@NAB@mastodon.me.uk if the filament is a couple of years old, how has it been stored?

could moisture have been absorbed by the filament? that can supposedly cause issues if it happens.

@NAB try changing the retraction setting - maybe putting it up a little? My other point would be what you already said you tried - increasing temps.

Two year old PETG is also likely to be quite wet, although I can’t see how this could be caused by moisture.

@krn Hi, I believe it is moisture. The filament is in a dehydrator right now, so I'll know when I come to test tomorrow morning!

@NAB Good luck! That’s fascinating - I’ve never seen moisture cause that sort of effect before.

@krn From what I can gather, the filament is exploding as it's laid down!

@NAB It's probably the filament it'self, have you had it for a while?

@wackomedia It turns out it is the filament 😢

@NAB
looks like the teeth grinding inside the filament instead of pushing it while printing(because printing infill makes a lot of back and forth movements)

I dont know your printer but can you try hardening (and if it doesnt work releasing) the teeth against the filament ?
maybe PETG is not soft enoughe and get hollowed instead of pushed

@NAB you have all the suggestions now. I would just add that I even dry pla, as it also suffers from moisture accumulation when stored for a while outside its orig packaging. (In my env)

@NAB @garius are you using a PETG-specific material profile in your slicer, and have you run through a printer calibration using PETG? Generally PETG needs faster travel moves (150mm/s) and much slower retraction speed (30mm/sec) than PLA.

This could also be the hotend leaking because PETG is very runny, so make sure the nozzle is tightened when the hotend is at printing temperature. The way I normally do it is to screw the nozzle all the way into the heatblock first, unscrew 1 full turn, then screw the heatbreak/heatsink in until finger-tight and/or aligned as needed. Bring the hotend up to temperature, then fully tighten the nozzle, likely there will be 1/2 a turn in it.