Nicolinux

Wait a second... I know this bottom surface from somewhere o_O Check out at 0:15 and play it in slowmo.

Thanks for the infos @ultiarjan. So I take it you are a believer now? Usually this issue doesn't bother me either when I print "organic" shapes. But for exact geometric forms with large flat surfaces it looks stupid and cheap. I'll try your tip about enlarging the hole for the grub screw when I'll disassemble the head again.

Alright, I worked on this issue again. Here is what I did: Disassembled the head again, took out the short rods, checked the linear bearings (alligned them X-Men style) and assembled everything again. Tightened the hell out of the short belts (again). Nothing changed :/ I printed the test square and aborted the print after the bottom was done. Here is the .gcode file. Print temp 215°. https://www.dropbox.com/s/8vilrm5zir0neiw/20mm-box.gcode?dl=0 That's right after I have assembled everything: Printed it again, this time with fans off: Printed again with fans on and flow at 105%: And one last print with 220° instead of 215°: During the maintenance I noticed something else. When the head is assembled there is one possibility to align the nozzle in the wrong way. This might add resistance to the filament because the PTFE coupler is not perfectly aligned with the metal collet and nozzle. And there is something else too. The spot where the PTFE coupler meets the nozzle should be tight and leave no gap since filament would expand and get caught up in there. It seems that the metal collet tilts the PTFE coupler slightly which leads to a gap on one side: On the right side, if you look through the hole, you can see a dark seam. That's where the gap is. On the left image, the seam is barely visible. I tested it with a dentist's tool (no dentist was harmed in this process): When I move the pointy end over that seam, on the left side I feel no resistance. But on the right side the tool snags onto that gap. The gap coincides with the rotation of the metal collet. If I turn the collet by 180° the gap would be on the left side while the right side is tight. I tried this with two different metal collets and different PTFE couplers. Also tested it with an experimental Olsson Block for 1.75mm filament. There it is the same. This might be the reason for the filthy under extrusion, but then I wonder why others don't have any problems with it. Btw. one tip about tightening the short belts. If you position the head in the center and tighten the belts, you might not be able to match the tension of the belts on the x and y axis. Try to move the head around and look for a spot where there is the most slack on one belt. Then tighten the hell out of it and repeat for the next belt. That was the only way to get the x axis on my UM2 to match the tension of the y axis.

Hey Labern, sorry I missed your reply. I already have it on my radar. Next time I need to print Robert's feeder, I'll take your mod. Thanks!

Hey Didier, sorry to be so thick headed, but I don't understand what you mean with the alignment of the four lines of the bearing balls. To me these lines look a bit curved at their ends. But everything is static and symetrical. Or can one relocate/move the inside of the ball bearing? Here is a picture: As for the short belts, I do remember that tightening these did have some impact on the surface quality, but more on the fact that the walls/shells didn't touch each other. Looking at my last two squares, that's definitely the case too. However, last time I tried to tighten the belts, I had a very hard time to get one of the belts really tight. It seemed that no matter what I tried, it wouldn't keep the tension. I think I need to file down the stepper motor holes a bit so I can push the stepper down and tighten the short belt(s) more.

Ok, so the linear bearings right?

Didier, which bearing do you mean? I don't get it. The linear bearing on top of the head? You have to pop out the thin rods in order to take it off right? I always wanted to avoid that.

Hm, I don't know... I hoped this is the solution, but for me - it is not. Here is what I did: Updated the firmware to the latest stable version (15.04.x). Disassembled the head and replaced the PTFE coupler. Then I printed a square with the following settings (I did abort the print right after the bottom was finished): layer height - 0.2 infill - 0 speed - 50 temperature - 215 It looks like this... There is even under extrusion on the outer walls :( Then I removed the board cover at the bottom and re-routed the feeder cable. It looks like this: Then printed the same .gcode file again. No under extrusion on the outer walls, but still sucky surface. I hate this issue.

Hi, ich frage mich wer sich durch den wall-of-text durchgekämpft hat Eine Info zu igus Gleitlager. Sie bieten auch Filament an. Damit ist man flexibler und kann so die Gleitlager selbst drucken: http://www.igus.de/wpck/12019/iglidur_TriboFilament?C=DE

Oh and there is something else too - forgot to mention it. As of the last two PTFE coupler changes, I noticed that when the filament passes the spot where the coupler, the metal collet and the Olsson Block meets, it snags onto something and has a very hard time to pass. Then when the pressure builds up, it snaps and passes with great speed. This can't be good under-extrusion wise. I wonder what it could be. I have checked both the coupler and the collet and also the Olsson Block. The connection should be smooth. I can't really test for gaps because there is no way to look "inside" where the filament passes while it is assembled. I have searched for an endoscope camera but there is nothing consumer grade to be found that's thin enough. I should have counted how many times I have disassembled the head until now. I think I am close to the three digits

Alright I got an humidity scale (or whatever it is called). When I put it right in front of the UM2 it measures 68%. On top of the UM2 it is even more - 71%. I guess that's quite a lot. @DoctorH: What did you measure? It seems my entire appartment is pretty "wet". There is no spot that's under 60%...

Hm, ok. Das ist schon merkwürdig. Gut aber merkwürdig Falls dir etwas auffällt, dann sag bescheid.

Mache mal bitte ein Foto davon. Es ist dann viel einfacher zu erkennen was los ist.

Ist mir nicht bekannt. Aber aus Metall ist das schon Overkill... Ich denke nicht dass der Verschleiß so stark ist. Ich nehme an du benutzt bereits diesen Feeder hier: https://www.youmagine.com/designs/alternative-um2-feeder-version-two

Hast du in Cura die "Gcode Flavor" umgestellt? Normallerweise hat der UM2 UltiGCode eingestellt welches seine eigene Startup-Sequenz am Anfang eines Druckes hat.

But back to the initial issue. Many people have tried many things. It is hard to compare results because every printer is different _and_ the environment (humidity, temperature...) differs too. @SandervG I think it would be best if you could fetch one of those problematic printers and test it at the UM HQ. As far as I know, @Labern's printer should be available. Anyway, over time I have tested the following (mechanical) areas and I would exclude them as the reason for the problem. Of course I've done tons of firmware resets and upgraded the firmware too over time. But these are only the mechanical parts that I focused on: Nozzle - tested it with the standard nozzle and the Olsson Block with tons of other nozzles Feeder - tested with the standard one and Robert's feeder. Bowden tube - Bought a new one and tested it. PTFE coupler - Tested a few... Metal collet - Is this the correct name? I mean the metal thingie where the PTFE coupler is inserted into. Swapped this one out too. There are two other components that I didn't test. Board - I've so had it with swapping boards between UM2's... So if someone has access to two UM2s might want to test this case. Feeder stepper - Might be something as easy as a faulty stepper of maybe some very ugly error that happens only under certain circumstances. Metal rods - Maybe some rods are bent in such a way that they move the head slightly up and down in some areas. This might produce the under extrusion like effect with the layers not touching. Next things I will try are the humidity test/problem and feeder calibration.

Ok, was hat sich geändert?

If the feeder were to wear out, it wouldn't recover so well after the hickup. In @shurik's case (apart from tangled filament) I could think of bad filament where the diameter changed drastically in one spot. A friend of mine had another related error. He seems to have stored his filament in such a way that only one side of the filament roll was dried. His prints failed regularly because the diameter changed a lot on the dried out segments.

@esteban-pacheco: I owe you a test print like a said a while ago. Since you did not provide all print settings I printed a 25mm X 25mm x 5mm square with the following additional settings: layer height - 0.2 speed - 40 It looks like this: Perfect surface - WTH!?!??

If you have been printing a lot, you might have had to change the PTFE (teflon) coupler on your UM2. But you don't need to throw the old one away. Just cut off the offending tip and you can keep using it. Just make sure you don't cut too much away. I'd say no more than 2mm - 2.5mm. The coupler will be inserted further down inside the metal thingie (what's its name?) but it still works.

Here is another hint that it is related to under extrusion. I was testing an experimental nozzle and had this result:

Ja aber eigentlich auch dann nicht. Das "skippen" ist kein gutes Zeichen.

Yep, Guglielmo is right. This is the best one. I added a bit of Kapton tape on the inside where the nozzle is closest to the fan shroud. Warped a bit eventhough it was printed with XT. Might try ABS next (but I printed a lot at 260°).

Wegen dem Skipping am Anfang - das könnte daran liegen dass dein Bedleveling zu straff ist. So dass die Nozzle zu nah am Druckbett ist. Bei mir kommt das Skipping nie am Anfang.

Hey neotko, do you have a link (or links) for those ptfe pieces/coupler? thx