I often have a bit of filament (mostly PETG-HF) that remains hanging from the nozzle after a print. It can be a 2mm or so bit sticking out, sometimes it’s a tiny clog, and of course there is a bit of filament remaining inside the nozzle. That nozzle is brand new and i print with the door open to prevent heat creep too.
Is it ok, to finish purging the hotend, to simply turn the heat on at PETG-HF melting tem (250°C or so) to let the filament drip out, or is it bad practice?
This is oozing, not dripping. Filament oozes because it’s absorbed moisture, which expands when heated, which pushes filament out of the nozzle. Drying it will eliminate this problem. Dry filament will not ooze.
However, if you don’t mind the negative effect it has on print quality, you can just ignore it. You don’t need to purge the nozzle of anything. When you start a new print job, the printer will purge the nozzle on its own.
1 Like
I see. The reason why I worry about it is that I’ve had several instances where the printer initializes and then gives me a message that says that there is an obstruction preventing proper levelling.
The X1C cleans the nozzle tip before it does bed leveling. It heats it up and then rubs it off on the tab on the back of the plate. As part of that process, it waits for the nozzle to cool to 140º, which is lower than the melting point of the plastic, specifically so that the nozzle can’t ooze while homing and leveling is underway.
If it complains that there’s an obstruction preventing leveling, it’s for something else. The odds are there’s a scrap of filament or a flung-off poop resting on some part of the Z axis and blocking the bed from getting all the way up. But I think once I managed to install my build plate slightly skewed and that interfered with homing.
3 Likes
Thanks for the clarification. I’ll keep an eye out for these obstructions then, and I’ll rerun the drying function on my partially depleted spool of petg-hf. I weighted it before doing it, and after 4 hours in there I’ll check ih it lost some water.
Drying inside the printer really isn’t very effective, I’m afraid. IMO It just doesn’t get hot enough. You really need a purpose-built dryer. For filament like PETG you’re going to want to get it north of 65ºC for a few hours (meaning, you have to give it a few hours to heat the whole spool up, and then wait a few more hours for it to drive the moisture out).
2 Likes
This happens even with dry PETG. You can try increasing retraction length or reducing nozzle temperature.
2 Likes
I disagree. It doesn’t happen at all with PETG I use, that is properly dried.
Filament shouldn’t ooze to any significant degree (regardless of type). Adding more retraction to address oozing is a band-aid solution and not a fix. But thoroughly drying will eliminate it.
I print with PETG all the time. Printed this out of PETG just this last week. Zero stringing. No oozing. The nozzle hasn’t been touched since the print finished a few days ago and there is no filament sticking out of it.
My PETG was dried. 70ºC for 24 hours. Also helps that it’s early Spring here so the ambient humidity has been and still is pretty low.
I print in Nylon a lot, too. Nylon absorbs moisture even more than PETG. Dried out, it doesn’t ooze either.
3 Likes
About the printer not running hot enough for drying, the setting on the X1C for PETG says 80°C for 12 hours. Is that really not enough?
The wiki temps worked for me when I was drying PETG, PC, ASA, or PA with my X1C heat bed. It was inconvenient because I was forever waiting for the filament to dry instead of actually printing, and it was slow, but it worked.
The issue with determining how long to dry filament is that you never know how much moisture is in the spool at the start. Maybe 12 hours is long enough, or maybe your spool is extra wet. You can dry, then test, then dry some more if needed.
I weigh spools on a cheap digital scale, then dry until the weight stabilizes - less than a gram lost in an hour.
I did just that. My spool was 661g, I thew it in the printer for drying for 4 hours, it lost less than 1.5g… so really, I wonder.
Yes, it’s not. Because that’s the build plate temp. You’ll be lucky if the chamber temp gets higher than 45ºC. And it’s the air temperature that matters, that’s what heats (most of) the filament (except for the filament on the roll that’s closest to the build plate - that will get hot enough).
Remember, plastic is an excellent thermal insulator. It takes a fairly long time at the target temperature before the entire roll of plastic has been heated up. And once temperature is reached, it takes hours for the moisture to diffuse out of the filament. If I’m drying a filament like PETG or PA, it gets 24 hours at 70ºC before printing. The equivalent exposure in the lower temperature build chamber is probably a week or more…
The build chamber drying method is better than nothing if it’s all you’ve got, but it’s not a replacement for a real dryer.
2 Likes
I did a couple ofshort tests with the 80°C heat bed.
Covering the spool with old spool box with the lid cut off, the air temperature in the middle of the spool reached 53°C after an hour.
Using the Bambu filament drying box, the air temperature peaked at 54°C after an hour, in spite of the six holes in the top.
These lower temperatures are why the Bambu-recommended heat bed drying times are 50% longer than using a dedicated dryer at 65°C.
In both tests, the chamber only reached 30° C.
I also see that the Bambu filament guide is now suggesting 75-85°C for PETG-HF heat bed drying, so adding a few more degrees might improve drying a little.
Pretty sure PETG (dried) still oozes. It’s not just moisture. The filament itself also expands. For example the Bambu PETG-HF would do this even if you dried it under 60C for 8 hours.
1 Like
I only print with PA, PETG, ABS and ASA (well, I tried some HIPS last week and was pretty happy with it, so I might start printing more with this plastic). All of these have high water absorption. If I don’t dry them, they ooze. If I do dry them, they don’t.
I can’t remember the last time I messed with retraction settings. And I’ve been FDM printing since around 2010.
But my definition of “drying” is 70ºC for 24 hours minimum. A unsealed roll of PA might go for 48 hours mid-summer when ambient humidity levels are highest. 60ºC for 8 hours is IMO nowhere near enough time or temperature for filament in an unknown state. For a full roll of plastic, that’s probably barely enough time to get it all up to temperature, and not close to the time it actually needs for drying. Once it’s hot, you have to keep the plastic hot for many hours for the moisture to have the time to diffuse out of the plastic. Diffusion is a slow process. And plastic is a good thermal insulator. It doesn’t like to get hot.
If your PETG is oozing after drying for 8 hours at 60ºC, try it again after drying for 24 hours at 70ºC.
3 Likes
All filament expands. It’s being heated, and it’s going from solid to liquid form. It has to expand. That expansion increases pressure in the nozzle and it can push a little filament out. But if the extruder is extruding, the pressure in the nozzle is much higher, and when the extruder stops extruding the pressure in the nozzle drops to zero. The plastic that’s already in the extruder is already hot and has already expanded and the “overpressure” that expansion caused went out the nozzle during extrusion. You might get a little tiny blob of filament if the extruder stays hot without extruding. But the only way plastic can continue to be driven from the nozzle when the extruder isn’t running is if something is continuing to push it out. Water turns to a gas when it’s hot enough and that pressure is what drives excess filament from the nozzle.
Which is also why wet filament might “pop” when printed, as steam pockets get pushed out the nozzle they make noise.
2 Likes
1,5g loss actually shows that it is working. A few grams do make a large difference.
If you measure again after say 8, 12, 16 and 24h, you should be able to see a reduction in the loss.
Also make sure you change your desiccant in ypur ams if you have one. I bought a hydrometer to put inside my ams and I have noticed that when it hits 20% humidity thats when I need to redry my filament and change the desiccant. The number reporting from the ams never changes.
It happens because the Machine Ending gcode finishes print, then does a few things before turning off the nozzle, resulting in some oozing, and the printer doesn’t rewipe until next print is started.
Put this M104 S0 here
You can see the offending delay followed by their intended ‘turn off hotend’ here:
By the time the printer actually turns off the hotend, we’ve retracted, moved around, turned off bed, turned off fans, wiped, pulled back filament into AMS (which can take awhile compared to the rate of oozing), moved around, wiped again, then turns off. Giving the nozzle a good 20 seconds before the temp falls passed oozing temperatures.
1 Like
I’ve never tweaked values before. Where do I do it? I know, I sound dumb ^^;