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protoprofessor

UM2 brim underextrusion after about 4 passes

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Hey there UM hivemind. This week I've been experiencing an issue with my UM2 where the brim and support structure of a large PLA print appear to be underextruding resulting in failing part adhesion as the print gets further underway. I've leveled my bed several times and cleared the nozzle using the atomic method twice...to my eye everything seems to be in order but I continue to have the problem. I'll note here too that on maybe the first three or four passes, the feed seems to be good - nice and strong and thick, you can see in the photos that the initial outermost brim ring looks pretty much how its supposed to at which point the beads start to get more anemic and occasionally spotty. I've done this print several times and the behavior is consistent even after leveling the bed and cleaning the nozzle.

If anyone has any ideas please let me know. Once again, this is on a UM2 using PLA printing at 230° and 50 mm/s (and I am using the glue ;) ) Thanks in advance!

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My machine has been on for 346:35, printing for 281:20 and gone through 176m of material.

It's tough to get a good photo with the white filament - the impression is actually a bit stronger than this picture indicates. The feeder drive seems to have a pretty good grip on the material but even so I do hear it slipping with a bit of frequency during printing. The tension on my feeder drive is pretty close to the maximum but there is a little a little room to tighten it a bit more.

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Is there a good photo tutorial on breaking down the printer head to check the PTFE coupler? Would be great to know what I'm doing before I start monkeying around with it. Thanks for you reply labern.

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Alright, sorry for the radio silence...had to step away for a few days because this issue has been driving me a little bananas.

I can confirm now that the problem does not lie with the PTFE couple. I removed my teflon coupler and it seemed mostly okay but I could observe the beginnings of the bulge pocket so I ordered a new ceramic part and installed it just to be on the safe side. I also installed a spare bowden tube I had lying around for my own sanity. Releveled the bed. Loading the filament is smooth and the hot end is extruding nicely, no skipping or apparent resistance that I can see. Removing the bowden tube and manually feeding the filament by hand does not demand any great deal of effort, Labern. Everything seems to be functioning as it should.

However, my first print still exhibited the problem. Initially the flow was strong but pretty shortly the motor began skipping and my extrusion became pretty weak and crappy with clearly defined gaps between brim lines. I would say the motor is skipping about on the order of every eight to ten seconds or so. Perhaps I should play with my speed settings..it's just super strange to me that I've been successfully running the default settings for about a year and suddenly my machine's behavior changes so abruptly. Here's the aborted part shortly after the brim was laid:

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If anyone has any other suggestions I'm all ears, I'll report back once I've tested some alternative speed and temperature settings.

Oh, valcrow, I double checked and my initial layer height is good. Thanks for the suggestion though!

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I found out that my issue is somehow Cura-based.

While looking at my Cura interface earlier this afternoon (I am running the latest 15.04 btw) I realized not only that a lot of my color indicators appeared to be missing in the layer viewer, but also that my toolpath lines seemed to be super spaced out. I saved my current profile, and then reset the profile to default. Voila - everything was instantly fixed, and the resulting toolpath is printing perfectly right now without any skipping or under extrusion.

The kicker is that after comparing all of my critical settings, almost all of my numbers were pretty much identical between the two profiles so I have no idea what is accounting for the huge difference. Did my old Cura profile somehow enter some kind of weird buggy state? Has anyone experienced something like this? Because as far as I know there IS no option to set the gap size between brim lines, but somehow my brim lines are crazy far apart in the old bad profile and I have no idea what setting, if any, is causing this.

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Would be curious to know if anyone has encountered anything like this. In any case, I'm all squared away now and back in business. Thanks to everyone that replied with suggestions!

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Edited by Guest

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Check your 'fix horrible' settings between the two profiles in the expert menu. It looks like your mesh has holes, interpenetration or other errors and Cura will slice it funny.

Fix horrible A or B (i don't remember) usually fixes the most common mistakes but sometimes fills in holes that you don't want. A REALLY early profile might have turned off fix horrible. It was only on by default later on.

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