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Temperemental under extrusion problem

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Hi guys, I thought that I had been pretty fortunate in not having major issues with the UM2 after using it for the last 4 or 5 months. Unfortunately i'm encountering a strange and persistent underextrusion problem. I started getting really bad prints about a month ago. It would print either really badly or sometimes just part print. It is no fun coming back to it 6 hours into a 10 hour print to find it happily whizzing away in mid air with nothing coming out! After reading some very helpful advice on here I increased the nozzle temp. to 230 and, sure enough, I went back to having pretty good prints. For about a week anyway. The quality started slipping again until this is what I was ending up with.


It had pretty much the consistency of an ice cream cone and obviously useless. I bumped up the temp to 235 and got a perfect print of a different object. (didn't want to chance the first one again as it was 6 hours)

Thinking that I had solved it I set up another print. Absolutely nothing was being extruded. After around 8 atomic pulls I am still having no luck with it. When I manually extrude, the filament flows ok and will extrude with very little pressure although once I start into the change material cycle the machine can't seem to extrude any and I get the loud clicking from the feeder. I have noticed that I do have to jiggle the filament about a little bit to get it into the nozzle. if I try a print and am not quick enough to abort, the filament gets ground down like so:


And I have to end up snipping the damaged bit off and pulling the filament out by hand, which is a waste. The end which was in the printing head seems to be intact which makes me think that it isn.t even getting into the nozzle.

It just strikes me as odd that I can have a run of good prints and suddenly start getting crappy ones or none at all!

Here are the settings that I've been using

Temp. 235

100% Fan 60

layer height 0.1

shell thickness 0.8

retraction - min. travel 1.5

                   enable combing All

                    min. extrusion before retracting 0.02

z hop 0

Bottom/Top thickness 0.6

Fill density 20%

Print Speed 50

I do have to add that I am using only one of the blue clips, at the printing block end of the tube. Would this realistically make a difference?

I'd certainly appreciate some opinions as I've totally run out of ideas. My next move is to dismantle the block and see if anything is warped in there blocking the filament from getting in to the nozzle. If anybody has any ideas that doesn't involve dismantling the block i'd be very grateful! Thanks.

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Have you done an atomic pull recently? If you have, post the result.

Usually you can tell by the shape of the pull if you need to replace the PTFE coupler. If you have trouble doing an atomic pull at 90C, as in the whole nozzle assembly moves with the pull, then you've likely got a pocket in your PTFE and needs to be replaced.

4-5 months of use is probably around the time where you have to change it out.

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Hi and welcome :)

Thanks for the advice! Yeah the printer has seen a lot of use! I'm thinking that I actually have two separate issues, the coupler and the under extrusion.

I came up with a kind of work around that made me think this.

I tried changing material (again!) with no result. Instead of removing the filament I took the tube out and, sure enough, the filament was intact and not enough was past the end of the tube to have been reaching the nozzle. I moved the material a bit further forward then reinserted the tube, jiggling it about until I was sure the filament was far enough in to get past the coupler.

Tried a print and it worked. Still getting some under extrusion but not as much as before.

It's hardly a permanent solution so, looks like I need to replace the coupler and then worry about the under extrusion.

This explains why the filament isn't going where it needs to be and also the grinding at the feeder but I'm still stumped about the under extrusion issues. Would a knackered coupler cause it?

I would check the Teflon Coupler and most probably replace it. Have you used the printer a lot?

To check and change it check this page


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Thanks for all the help guys. I'm using colorfabb stuff so hopefully that won't be the problem. It's actually printing quite well now, not perfect but acceptable after I did the workaround.

I'm pretty much convinced that it's the coupler so next time the issue comes up, and there's always a next time, I'll replace it as a spare hot end pack came with the machine. Thanks again guys, it's a great community here.

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