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latreides

Extrusion woes?

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I tried printing some flex recently and it didn't go very well.  I cleaned out the nozzle and the feeder to make sure that there wasn't any remaining flex debris before I went back to my normal printing routine.

I have not been able to make a successful print since.

The biggest issue seems to be that after I complete a print, the next time I try and print, it has feeding issues.  It won't feed at all until I change material (to the same material), and then it "works".  By works I mean that it will print, but the first layer is almost always garbage.  I get what appears to be bursts of over extrusion.

extrusion_bursts.jpg

The picture shows the dark lines/ridges where its extruding about 2x as much filament and then it starts printing the normal amount.  This happens on a regular, repeatable basis (about the same gap between over extrusions).  I have tried printing this nearly two dozen times and it always has the same result.

I tried with Cura 2.6 and Simplify3D, these didn't change anything. I tried with different materials, different temperatures, and different tension settings, these didn't change anything. I know its not the model, because it will (sometimes) print it just fine.

The rest of the print (after the first layer) appears to go well; although it might be difficult to see if this pattern is happening after the solid layers.

I have taken the feeder apart multiple times to see if anything was stuck or clogged and it seems ok. I have also taken the nozzle off and made sure it (and the parts it connects to) are completely free of filament. This hasn't changed anything. Does anyone have any ideas on what could be happening?

Edited by Guest

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What happens on the next layers if you continue printing? Does it keep extruding so irregularly, or does it level out nicely?

I sometimes see a bit of irregular extrusion too in one of my printers, but only on the first layer, although far less than yours. Then it smooths out. So I don't really care, as it is only one layer.

In some brands or colors of filament, this effect is much stronger than in others. Also, when the nozzle is leveled rather close to the bed, to get a smoother bottom layer, the effect is stronger.

I am not sure what causes it, but I guess that in the beginning the temperature is not yet totally stable, or that there are variations in molten volume in the nozzle, since you don't have a nice steady stream of filament yet in the beginning. I guess it is like in a chemical plant, where you always have process variations and swings on startup, until all distillation columns and equipment is on temperature, and a steady flow is established? Then things smooth out.

But of course, there could still be other causes, such as a worn-out coupler, or variations is filament diameter, or filament that has trouble sliding through the bowden tube smoothly, so that pressure builds up irregularly, and then it jerks forward? Or something similar?

What happens if you print a skirt of 30 lines around the object, just for test?

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What happens on the next layers if you continue printing? Does it keep extruding so irregularly, or does it level out nicely?

 

It appears to print nicely after the first layer. Its difficult to tell because its mostly infill.

 

I sometimes see a bit of irregular extrusion too in one of my printers, but only on the first layer, although far less than yours. Then it smooths out. So I don't really care, as it is only one layer.

It makes for a very rough, ugly bottom.  Its not really an acceptable solution.

 

I am not sure what causes it, but I guess that in the beginning the temperature is not yet totally stable, or that there are variations in molten volume in the nozzle, since you don't have a nice steady stream of filament yet in the beginning. I guess it is like in a chemical plant, where you always have process variations and swings on startup, until all distillation columns and equipment is on temperature, and a steady flow is established? Then things smooth out.

I am relatively certain that this is not its cause.  If this were the case then printing a small part would have even worse issues (and they would likely persist past the initial layer).  Its actually the opposite.  Smaller parts print perfectly, first layer and all.

 

But of course, there could still be other causes, such as a worn-out coupler

I recently replaced the coupler with a new one from 3d solex.  I am not sure what the coupler does, or how it could cause this issue, but the one I have is pretty new.  It looks perfect when I disassemble the extruder.

 

or filament that has trouble sliding through the bowden tube smoothly, so that pressure builds up irregularly, and then it jerks forward? Or something similar?

This is actually what it sounds like.  My working theory is that the smaller parts I print have more retractions so the filament is moving back and forth more often, where the larger parts print in longer runs with no retraction, giving it more time to "stick" to the bowden tube.  While its doing this, its slowly running out of filament (I actually have seen some thinner than normal sections that give more evidence for this), and then the push when the pressure is enough to overcome its friction is responsible for the flood of filament.

 

What happens if you print a skirt of 30 lines around the object, just for test?

I plan to try and oil the bowden tube to try and get it to slide better and see if this solves the problem.  I have read that some people have had success with this on other printers.  I will try a large amount of skirts if this doesnt produce better results.

Edited by Guest

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An update to this, and a question.

Oiling helps a lot, but it doesn't make the problem go away entirely. In fact I have started to notice a new problem (or an old problem getting worse) which (may) be the source of the original problem.

The filament seems to be catching on something right at the end. I thought that it was getting friction stuck in the Bowden tube, but that doesn't seem to be the whole situation.

In the extruder, somewhere, the filament is getting stuck until there is enough force from the feeder, at which time I hear a loud "thunk" as the filament slips off of whatever it was stuck on and starts feeding.

I have very recently (roughly around the time the problem started, though its hard to tell) replaced the coupler. I have taken the extruder apart a dozen times, and everything looks fine, everything goes together smoothly, but it makes me wonder if there is something I might have overlooked.

When putting on the coupler (or reassembling the extruder), is there anything I could have done wrong that would cause the filament to snag on something?

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It could be worth checking all of the fans on the print head are working correctly, especially as the problem seemed to start after a head dis-assemble

I have had many problems in the past with the connectors for the fans which are all in the head area

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I took the extruder apart again and I noticed that the Bowden tube was not cut flat.  It was at an slight angle.  My working theory is that the 'tip' of the angled part of the Bowden tube was making contact with the coupler.  The 'tip' was in just the right place for it to guide the filament into the coupler until I replaced the coupler and thus removed the tube and reinserted it.  At this point the 'tip' was at some other location, leaving a gap between the Bowden tube and the coupler where the filament made contact with the Bowden tube.  It is this gap that the filament is catching on.

I have cut the end of the Bowden tube to be flat, and have inserted filament into the machine multiple times without it catching.  I am not sure if this will solve my original issue, but I am hopeful.

Edited by Guest

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Have you tried this? Remove the bowden at the print head. Heat up the nozzle manually to the normal print temp. Check if the little back fan works indeed. And then manually feed filament into the teflon coupler and nozzle directly, without bowden tube. Keep an eye on the temperature. Does that go well, and keep going well? Or does that cause jerks, stops, irregular friction, or whatever? If you can feed 10cm of filament through smoothly in this way, that should exclude the nozzle and coupler from the cause, I think.

And what happens if you disconnect the bowden tube at both ends, and manually feed filament through it? Does it slide smoothly? And then connect it again at the nozzle, and feed filament manually all the way from the back to the nozzle? Does that feed well and extrude smoothly?

I could also imagine that some flexible filaments do get too sticky and slide very difficult when warm. Like soft rubber or siliconerubber which does not slide against a surface smoothly, but always jerks.

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Check if the little back fan works indeed.

I have not checked the fan yet, but I don't have the fans on during the first layer so I am not sure what difference this would make.

And then manually feed filament into the teflon coupler and nozzle directly, without bowden tube. Keep an eye on the temperature. Does that go well, and keep going well? Or does that cause jerks, stops, irregular friction, or whatever?

So the "thunk" went away when I cut the Bowden tube flat. I have changed filaments half a dozen times since then and haven't encountered it again.

If you can feed 10cm of filament through smoothly in this way, that should exclude the nozzle and coupler from the cause, I think.

Does that feed well and extrude smoothly?

With the Bowden tube connected I have let a couple hundred mm of filament flow through and it all looks good.

The original issue persists. The oil seemed to help some (the hills/valleys are less extreme), and when I change the first layer thickness to 200% it hides it a lot better, but it doesn't fix the problem.

When I bought my UM2+ a couple months ago, it worked perfectly. Now I cannot reliably print anything with a large flat surface or anything that takes more than 8-12 hours to print.

With the oil and 200% 'trick' I am OK with the results (they are not great, but usable), however after 8-12 hours of printing, it will stop extruding. I first guess is the feeder is slipping. There doesn't seem to be a major clog. I can perform a 'change filament' operation, cut the filament back before the part the wheel ground up, and insert it back into the feeder and it has no issue extruding.

The tension on the feeder is in the middle, or slightly lower (I have tried both), and I am using PLA.

I see that there is a UM2 feeder replacement, but that seems to be only for UM2 not UM2+, is there a recommended feeder replacement for the UM2+?

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If anyone is still following this topic (or wanting to help trouble shoot with me), something I noticed recently might help diagnose the problem.

When I change filament, sometimes it will get "stuck". It wont actually extrude any filament on the "wait for filament to extrude" step. When it does this, I "change filament" again, and I notice that the end of the filament that comes out is perfect. Its not melted or attached to any of the remaining fragments that were in the printer before. This leads me to believe that its actually getting jammed in the hot end. I have taken the hot end apart a dozen times now, and it all looks great.

The only part that I could imagine it getting stuck on is the very edge of the coupler, but the coupler is new and the end of the bowden tube is as straight as I can make it.

If I round out the end of the filament before I feed it in, it tends to work every time. Could it be that the burs from the feeder gouges in the filament are somehow getting caught on some portion of the hot end, and jamming for log enough for the feeder to slip and grind?

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I wonder if the problem is caused by a small deformation at the bottom of the PTFE coupler, next time you dis-assemble you could try to push some filament through the coupler it should pass through quite easily.

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I wonder if the problem is caused by a small deformation at the bottom of the PTFE coupler, next time you dis-assemble you could try to push some filament through the coupler it should pass through quite easily.

So I removed the coupler, and it has a little ring of black on the tip that is raised a bit.

coupler.png

When I slide a piece of filament through, there is a little bit of friction as the slightly deformed end catches the notches in the filament from the feeder. When I try and pull it the other way through (as in a retraction) there is more friction.

Its not a lot of friction, would that cause this problem? This is a brand new coupler from the @gr5 store. I have a hard time believing that its at fault, but I have exhausted every other possibility.

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The PTFE coupler does not look too bad, I would try a 3mm drill to clean up the exit point (to be done by hand not using an elecrtic drill).

I would also recommend an I2K insulator which protects the end of the coupler, I have had one in my printer for probably 500hr of printing "It serves as an insulator between the PTFE coupler and the hot end" available from http://3dsolex.com/product/i2k/ and maybe other places

Last time I dis-assembled the print head the PTFE coupler was still like brand new

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Talking with @gr5 over email about the coupler, I was given some advice for installing it. I removed the coupler, tried to clean it up as good as I could, and reinstalled it.

When I originally installed the teflon coupler, I didn't adjust the steel coupler at all. This time through though, I "loosened" the steel coupler (which brings it tighter against the teflon coupler) to put more pressure against the teflon coupler.

When I normally attach the bowden tube, I push it all the way down in the slot, and then slide the blue clip over the white base to keep it from coming out. I didn't realize this, but when you slide the blue clip onto the white base, and it raises the base, it will also pull the bowden tube up some, leaving a gap between it and the teflon coupler.

What I did to solve this was put the blue clip under the white base just a little bit. Enough to raise it up as much as it is going to, but not enough to actually prevent the bowden tube from sliding. Then I pushed the bowden tube firmly into the base, and slid the clip over.

Its not perfect (I think the teflon coupler is permanently damaged) but it is printing a lot better.

Catan.jpg

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What I did to solve this was put the blue clip under the white base just a little bit.  Enough to raise it up as much as it is going to, but not enough to actually prevent the bowden tube from sliding.  Then I pushed the bowden tube firmly into the base, and slid the clip over.

What I do is loosen the 4 thumb screws, attach the bowden normally and then tighten the 4 thumb screws which pushes the bowden into the teflon part.

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What I do is loosen the 4 thumb screws, attach the bowden normally and then tighten the 4 thumb screws which pushes the bowden into the teflon part.

What I did was easier for me, but I will try this way the next time I assemble it. The whole point though, was that the way I was doing it, was likely to result in a bowden tube that is not firmly seated in the teflon coupler. Thank you for this insight.

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