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Nicolinux

UM2 retracts after print way too far

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Hi,

I noticed that after a finished print the filament is retracted quite a bit. This is actually a problem because the filament is transported very far up, past the teflon piece. On the next print, the filament is pushed down again, through the teflon piece. This will certainly lead to increased wear because the filament tip tends to form a significant buldge which is squished through the teflon for every print.

retraction before print

filament Tip with buldge

Depending on the reason why the filament tip forms such a buldge or how pronounced it is, this might explain the underextrusion problems of some users where the teflon piece gets deformed.

What do you think?

Tested with firmware 14.09.

 

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I've noticed the extreme retraction as well. I've noticed myself checking more and more lately on the beginning layer of prints to make sure the nozzle is sufficiently primed, and the first layer is going down fine. I'm having to do this becasue there are times where it just doesn't prime enough, or for whatever reason the filament binds in the hotend/teflon, causing a jam. I used to be able to just hit print and walk away. Not 100% sure it's this long retraction, but it's definitely a strong candidate for being the culprit.

 

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Hm, right after the print, the bed moves down a bit (but fast) and then the head moves to the side. I don't think there would be a big chance of excess filament falling down. And even if, this lil strand of filament would be no problem to remove. I think teflon piece wear is by far more serious than that.

 

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But are you happy with the status quo? The prospect of the filament bulge passing through the teflon piece every time isn't something I'd would trade. I mean, this retraction after print is a somewhat recent change if I remember correctly (since 14.x). Even if PLA bakes onto the nozzle, the next time it is heated up it will soften again so it can be pulled out easily.

I'd love to hear Daid's thoughts about it.

 

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I agree with you Nico i think i sometimes have problems with that retraction as you said it can probably damage the Teflon, i had one or twice the filament stuck in the Teflon because it was too expanded.

I had to remove the filament by taking the Bowden off like in the Atomic procedure to get it out (was to hard to pull out from the feeder).

But indeed for things like woodfill it's probably a very good thing, anyway i would recommend cleaning the nozzle after every woodfill or bronzefill print to prevent blockage. Maybe it could be a parameter of the material?

 

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+1 :)

Is it retracting when aborting a print? I don't have the impression it does (I'm not home to test it).

 

It does in later firmware versions.

The idea of this retraction is to remove the filament from the hot-zone so it does not degrade while the hotend is cooling down. And heat from the hotend "creeps" up trough the filament melting more filament inside the teflon, causing problems there.

 

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