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Underextrusion / blockage... what do I try next?

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Hello, I have Ultimaker 2 and have been sucessfully printing quite large and complex PLA parts for a month or so (having initially wasted some time trying to print in ABS).

Now it is not going so well!! Just when I really need to get parts completed!!

I can only get printer to run for short periods (couple of minutes) before feeder clicking and underextrusion starts, sometimes the feeder will start grinding untill no grip on filament. This is printing parts which I have printed sucessfully before with same reel of filament.

I have tried a lot of things:

- Atomic nozzel clean (many times and nozzel seems fine)

- Printing at higher temperatures (this maybe helps a bit, not sure)

- Changing feeder tension

- Taking apart feeder mechanism

- Taking apart nozzel and cleaning up the teflon spacer.

- Checking filament diameter

It seems to be either the feeder is not man enough of I have extra friction in the system or maybe a dodgy temp sensor?

Can anyone suggest things I can try, or ideas as to what it might be?

Many thanks in advance


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Did you check the small fan cooling the nozzle end when your under extrusion occurs? It could be stopping. It's suppo to be on all the time. The one directly behind the aluminum block.

Also, check what the nozzle temperature reads until the under extrusion happens. Sometimes you can see Huge fluxuations.

How is your filament mounted? Is it on the factory spool holder clipped to the back or did you upgrade to something better with bearings?

Sometimes at the end of the spool the filament gets extremely tight coiled causing a tremendous amount of friction.

Just trying to give you some other things to check.

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Thanks for replys,

axsdenied, no I have not tried cleaning Bowden tube, I will try that next, thanks.

Personal Drones, yes I think I will order a fresh one just in case.

Chrisp, yes fan works all the time and I have a separate spool holder....

It could be that the coil bend in the filament is causing extra friction in the Bowden tube, especially if bowden tube has filament bits in it.

Any other suggestions plese let me know. Thanks.


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Hey Will_Design!

Were You able to solve Your problem yet? I got the same problem since about 2 months and I wasnt able at all to fix it ... Did the same as You did already but without success.

For me the problem starts after a certain amount of time (always different), then the feeder is doing a clicking sound and nothing is getting extruded any more.

If I let the printer cool down and try again another day I am not even able any more to get trough a successful 'change material' process any more, because the clicking sound appears again before any filament is extruded again. I am really getting desperate since I am unable to print since months. Ultimaker Support seems to be overtasked atm too. :(

Thanks for Your answer.


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Since you had abs in that nozzle I fear that it might be the culprit if you haven't found anything else from the suggestions above. When I use abs on the um2 I have to use the atomic method about 6 to 8 times at various temperatures to get all the abs out. I use leftover rolls of white and heat up the hot end to 250 C and manually push the filament through then let it cool to 60 C and manually pull out to clear the nozzle completely. Usually there are little black bits that are attached to the white filament. I repeat until all the black is gone. In order to manually feed I am using Roberts feeder which makes it easy.

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Did you look at the Teflon insulator (the white thing above the nozzle). After some time the inside deform and increase pressure on the filament causing feeder to click backward and extrusion to stop or be really hard to achieve.

You can try to drill the deformed part out for temporary fix but you should order a replacement if that is the issue.

drilling teflon piece with 1/8" drill


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