Furry stringy nylon layers??

[ScanHD 32]

Today I started a large ultimaker nylon print. The first layer and brim went down great!! (left side of first image) But the next few layers seem to be furry and stringy, and I can hear a slight crackle from the nozzle.

 

Is this normal? 

 

edit -

sliced with cura 4.0, and S5 is updated to latest firmware 

Layer height is 0.1 (fine) all print settings are standard cura profile for Ultimaker nylon

 

Edited January 4, 2019 by ScanHD

[ScanHD 32]

The nylon has been out in atmosphere on the machine for 2 weeks.... Is it possible that it's too wet? But the material already in the bowden tube stayed dry and therefore produced a good first layer??? 

 

 

 

edit- so i canceled the print, i wasn't happy with the way its looking especially as its for a client.

 

I have another, unopened spool of nylon so i thought i can print it with that instead, if my wet filament theory is correct. But before i did that, after clearing the bed, i restarted the print as a test to see if the first layer would be weird looking like the upper layers of the previous print....

 

To my surprise, the first layer went down perfectly, and now the 3rd layer is printing without issue also...so that rules out wet filament! The filament is fine.

 

Has anybody seen this behavior before?

 

My best (uneducated) guess now is that it was a partially blocked extruder, that was somehow unblocked when i restarted the print?

 

 

 

*as a side note, as i'm not sure its relevant, when i aborted the previous print the extruder still oozed for 30 seconds or more. Could this maybe indicate a blockage?

 

 

Edited January 4, 2019 by ScanHD

[ScanHD 32]

OK so i have been closely monitoring this print all day and i have discovered some very unusual behaviour. 

 

The print was going fine for the first few hours but then i saw the same thing happening as before. I was trying to find out what caused it when i touched the print head very lightly downwards and noticed that it INSTANTLY improved the print quality again.

 

i tried to show it in this short video...

 

 

hopefully you can see the line before i touch the head is terrible quality, then as soon as i touch the head everything returns to normal.

 

in the first couple of seconds of the video, the crackling can just be heard above the fans, and it also instantly disappears when i touch the head.

 

vibration maybe? under extrusion?

Edited January 4, 2019 by ScanHD

[Smithy 1,043]

I am pretty sure it is wet filament. Nylon is VERY hygroscopic and printing without a drybox or something like that can be a pain. A few hours are enough to "destroy" the spool, so if you say it is out for about 2 weeks then it was too long out in humidity. So you should dry the spool for several hours on the heated bed or in an oven.

 

I guess that the filament on the outside of the spool is more wet. So you started your print, the piece in the bowden tube was dry and the first layer was ok. But then comes the wet filament and you heard the sizzling sound and got a bad layer. I cannot say why the restart helped, but I guess the wetness is not the same over the whole spool. Additionally, the wet filament could or has clogged your nozzle a little bit.

 

So, dry your spool, use a new one in the meantime, but do some hot/cold pulls first to get a clean nozzle. And consider to buy a drybox or build your own if you have nylon prints of several hours. Nylon is more hygroscopic than PVA and PVA is already a pain to use in higher humidity.

 

 

[ScanHD 32]

thanks for your input!I actually already bought a drybox today so we are very much thinking the same thing there!

 

Im pretty sure its not the filament tho. I was thinking it might be under extrusion so i tried upping the material flow to 130% in the tune settings and the last couple of layers are looking really good!

 

could all this be down to an incorrect setting in a profile?

 

 

Edited January 4, 2019 by ScanHD

[Smithy 1,043]

It is possible, i.e. printing with the wrong temperature, but I still think it is/was the filament. Maybe just some meters and the inner ones are ok now, but the wet filament has already slightly clogged your nozzle. That could be the reason for your under extrusion and you compensate it now with more flow.

 

Clean your nozzle if you have finished your current print and then I would change the spool to the new one and print out of the drybox directly for your long print job.

[ScanHD 32]

great thanks! That would actually make a lot of sense.

 

I was thinking about a clogged nozzle as a kind of binary parameter.... it is or it isn't. But of course it can be partially blocked aswell which may explain the fluctuating results. I had no idea wet filament could cause a blocked nozzle either!

 

All part of the learning curve i guess!

 

 

[ScanHD 32]

just out of interest, if the nozzle was to suddenly unblock itself... would the 130% flow cause the print to fail?

 

I'm leaving this one overnight and was considering what the risks are...

[Smithy 1,043]

3 minutes ago, ScanHD said:

if the nozzle was to suddenly unblock itself... would the 130% flow cause the print to fail?

Hard to say, but I guess you will get over extrusion if it really unblocks itself, but I don't think it will unblock. More likely it will get more clogged with the time. But give it a try....

[ScanHD 32]

It survived, and it's looking great! 

 

9 hours to go! 

 

[Smithy 1,043]

Looks great, good luck for the next hours 🙂 

[ScanHD 32]

Just a quick update for those who are interested....Two very successful prints using this core, spool of filament and 130%material flow setting. 

Edited January 7, 2019 by ScanHD

[Smithy 1,043]

Thanks for the update.

Strange that it is working with 130% flow, but the result is great.