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Filament SWELLS and clogged inside PrintCore.

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I am printing PLA filaments.

I am experiencing under extrusion after printing for a while and later filaments not coming out of the nozzle at all.

I checked everything, feeder, nozzle etc. every thing works fine but.

When fail/clog happens:

If i remove the bourdon tube from the print core, feeder extrude filament just fine.

Then if I manually push filament(a fresh piece of filament or cleaning filament) into printcore, it extrude from nozzle just fine.

I noticed that the reason is filament going into the hot-end swells/enlarged/thickened up. and it seemed to be the reason why it is not pushing through the core:


Does it meant that I am printing in a temperature too high that it somehow melt and swells the part of filament before it reaches nozzle? Or am I printing in temp too low that the filament cant get liquefied enough to keep on the flow so that it stacks and builds up? Or is that a result of wrong retraction setting?

I am using everything default on CURA PLA setting on extra fine profile, except for the fact that I try printing in high temperature (220C~230C).

Any Help?


Edited by Guest

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I believe 230°C is too high for PLA, at least at normal default speeds. Then it would soon burn inside the nozzle and get brown. Try 210°C first.

Also, did you check if the little fan at the back of the nozzle does work well? If it does not, heat will travel upwards into the filament, and soften it way up there. This could cause blocking due to "swelling" (actually the half molten filament is squeezed together). This is for an UM2, I don't know how it looks in an UMO or UM3.

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I have not seen a material profile that goes that high in temperature.

in other printers I have found this to be a common cause of blockage.

it's heat creep where the heat travels up the material faster than it can cool and the material softens and compresses, this causes it to expand as it can't go anywhere else especially when printing fine as your extrusion rate will be slow. this expansion then causes it to get wedged.

you might have to do a hot and cold pull to make sure its cleared out.

hope this helps

PLA as a standard should max out at 210 but normal printing is at 195 to 200.

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Although printing with normal setting at 230 is quite high, in some cases it can be nessesairy. When printing with 2.0mm nozzle on UM2, with layer thicknesses of +-1mm. I need to go up to 250 te get the best quality of prints!

Besides that there are also quite significant differences between different UM's (even in the same batch). sometimes even having differences of up to 15 degrees difference between printers.

In you're case the fan, and adjustment of temperature as stated is probably the way to go.

If it is a old printer, you could also check if the ptfe tube above the nozzle could case this upswelling. But I would only suggest that if both other options given dont work, and the printer has been printing quite a lot.

Although prisumable it is correct, but do you use propper 2.85mm filament and not 3mm (3.00) filament? this could also result in a clock if the filament goes to the upper tollerance of 3.10.



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