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Problem with material flow UM2

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For the last months I have problems getting good prints. It seems that suddenly the printer does cannot get any PLA trough the nozzle. The filament push motor (do not know the correct name) retracts and almost at the same time only drops come out of the nozzle instead of a steady stream of material.


Thinks I have already done:

- Cleaned the nozzle (seemed to help for some time)

- Put the temperature to 225 C. (seems to help)

- Bought a new nozzle (did not make much difference)

- Cut a few centimetre of the bowden tube (because the end got damaged)

- Put a bit of oil in the bowden tube (seems to help a bit)

- Print in the front of the build plate (seems to help a bit)

- Used different filament (does not seem to make a difference)


But once in a while I still get prints as shown in the picture.
I think I have tried everything. What else could go wrong? Please help!!


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This looks more like what happens if the Z stepper *driver* overheats.  What happens is the driver shuts off power to the stepper briefly (less than a second) but long enough for the bed to fall a bit.  If you put a brick on there the gaps will be much bigger and you will know that is the problem.  The fix is to lower the current to the Z stepper which was a standard firmware update over a year ago.


But you could be right - it could be underextrusion.  If it used to work fine and you didn't change any slicing settings then it's most likely the teflon part.  It is considered a consumable so it fortunately is priced pretty low.


Also could it possibly have been a filament tangle?  Did you check to see if the filament is moving nicely?


If you are certain these two guesses aren't your issue I have a list of about 20 other things that can cause underextrusion.


Another quick test of the Z driver issue is to remove the cover and tilt the printer while it's printing and have a desk fan or window fan blow gently under the printer.  If this fixes it then let us know and I'll post more info.

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I think the Z- as is not the problem. That is because I see this happening on the first layer. (you can see it a bit in the previous picture on the brim.


The filament was not tangled, it was an almost new role and I use two extension for my filament




I have also already updated the firmware to the latest version.


The teflon part looked ok to me, a bit dark at one end (is that normal?) but it did not look deformed.


So what are the 20 other thinks that could be wrong.

(thanks for your help)


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From all you say, and if you ruled out what george said, i would really have a close look at the teflon isolator.


How many hours of print has it been through?


Also it's an ultimaker 2 so if it's an old one this piece wasnt that resistant in the early units.


Another possibility could be the feeder, assuming you have the black one that has a tendency to grind filament, maybe it needs a good cleaning.

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1000 hours printing!!! Yes!  change the teflon.  It needs changing more often than that.  The price from UM (and other resellers) is quite reasonable!  But don't get one from China as the teflon from UM and from 3dsolex is much better.

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4 hours ago, Massassi said:

How often should I change the teflon, (how many print hours). are there other parts that need replacing?

When it is worn out. That depends on the temperatures at which you print. Once above 210...220°C, the old teflon couplers degrade quite fast, especially when printing fast (=high internal pressure). When printing slow (=low internal pressure on the molten filament) and cool (=less thermal deformation and break down), then it lasts much longer. I usually need to replace them every 200 to 300 hours on my UM2 (non-plus), when mostly printing PLA at 210°C, and PET at 220°C. Apart from that I haven't replaced anything yet, and both printers have about 1000 hours. Although I made a few minor modifications, such as a compacter and low friction spool holder, and different bowden-tube clamps (to make them pinch the tube less).


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If you print at 240C and hotter it will "die" much faster than at 220C.  No one seems to have a definitive answer on this issue unfortunately.  Basically it works great for a while and then slowly you notice you have to print slower and hotter to avoid underextrusion and eventually you realize - "oh - it's time to replace teflon".  It always creeps up on me and surprises me.


I have one customer who has 3 UM2 printers going nonstop 24/7 and he says the newer teflons from UM and 3dsolex last 3 months.  That's just one datapoint.  I don't know what temperature he prints at.  For UM3 the teflon should last pretty much forever because even though the nozzle gets to 210C or 250C the teflon shouldn't get above 100C.

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After playing around with all sorts of thinks, I discovered the real issue.

It seems that the bowden tube  sometimes does not attack to the teflon tube. (see picture). This causes (cold) air to be blown in to the teflon tube and cooling the nozzle. I my case the clamp on the bowden tube, is warn out. (need to order a new one). For now I just turned the bowden tube around.

This seems to solve this problem. But still I think the force on the bowden tube and the clamp is to great and will cause this problem again in the future. (and with other users)



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