It may be that you’re trying to print too slow especially if you’re doing thin layers. Don’t forget that one of the effective coolants for the cold end is fresh filament coming in one end picking up whatever heat made it through the insulator and shoving it back down into the hotend, but only if the total flow rate is high enough.
sry for not reading the previous 21 comments, but I am very sure that the transition-zone of your hotend is too long. PETG has a bigger temperature zone at which it is going to get soft, so if your coldend isn’t cold enough, you geht a soft zone of filament right in the transition-zone. This is going to get pushed flat and thick and thus blocking/jamming the hotend. I bet, that when pulling the filament back out, you have a big “plug” on the end of the filament. If this is the case, you need either to print faster in terms of pushing more filament through in the same time, e.g. printing with bigger layerheight or just faster, or you need to work on your coldend/coldend-cooling.
Actually it looks like an air bubble. I think the retraction is too high, and the transition location is too high, so the retraction happens fast, the plug cools down too high and gets stuck. The plug isn’t sealing, thus why there is an air bubble.
@Stephanie_A I usually print with petg without retraction. You will get some stringing, but with high enough temperature and speed, it’s not so bad. Petg is a bit strange compared to other plastics. You will find that the onorthodox methods work better. Listen to @Eclsnowman and @raykholo . They are right. Personally I get much better results printing at 0.3 mm layer hight then with 0…2mm. Probably something to do with the bigger flow through the hot end. The only time I had a jam with petg was when my cooling system wasn’t working.
I print PETG on an e3dv6 at 0.1 with no problems. Layerheight can’t be the case. So: Did you grease the thermalbrake with thermal compound like e3d montioned in its newer assembly guides? This will help a lot with shortening the transition zone. The airbubble you see is generated by you, pulling it back out, not during retracts.
Ya, I greased the thermal break. It printed the last print ok. I’m printing another at 240c and 1.5mm retraction. So far no issues. I also cleaned out the hobbed drive, that probably helped too. I’m worried at this temp I won’t get good bridging.
I had good bridging with 240c. I was using esun PETG (actually inland brand but it’s been widely considered just esun rebrand)
After Rene’s suggestion I tried bumping my print speed up to 150% of normal and a tall, thin part I couldn’t get to print in the past did print quite nicely. It seems that heat creep may be my biggest problem with PETG then.
@Stephen_Baird I think the only time you need to print slow is for the top layers. I use at least four top layers with PETG.
I print slow because I get a lot of corner ringing/ghosting.
Keeping the mass off your extruder/bed (if it moves) will be the biggest factor for ringing aside from messing with your jerk and accel. I never print my outer shell above 35mm/s and unless I have my jerk down to 700 on XY I will get ringing.