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dgsharp

more under-extrusion problems

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I've been having more under-extrusion problems (UM2). The highest I've ever gotten on Illuminarti's cylinder test since trying it the first time was about 7, and I tried the other day and it was popping multiple times per loop, utter failure.

Lately there has been some kind of gap somewhere causing filament to pile up, so that when I go to change material or when I do the "HAS-CAP" hot-end cleanout procedure it leaves a big nasty bump.

 

mangled

I tore down the hot-end (except the extruder) and it's puzzling. I do the "HAS-CAP" procedure and I can see daylight through the nice round hole, but it's giving a ton of resistance, even at 230C. I forced some PLA through with it all taken apart and was able to see it push the teflon piece up in the air, filling the new void below the teflon part with a puddle of PLA resembling the shoulder on the PLA ends in the picture. So it seems to me like what I'm getting is a combination of unusually high pressure in the hot end, and a teflon piece that is moving up under that pressure, causing further problems. I have a very strange lip/groove on the inside of my teflon part (which I've seen in one or two pictures on here before, attaching pic), and they're sending me a new one, but I'm not convinced that's my only problem. This filament is slightly under-sized, and has printed very well for me in the past.

teflon part cropped

Is it possible that the pressure is so high in my hot end just because it's coated in a layer of built-up burned-on PLA / ABS / nylon residue that is acting as a thermal insulator? And if so, is it expected that the teflon piece would push upwards and create a void underneath it, or should it be held in place more firmly somehow? I've got clips on the bowden tube and there is no play at all there, but I've been careful not to tighten the knurled thumscrews on top too tightly as I've read about here.. I'm sure people will say that printing multiple materials should be avoided, and maybe that's true..

Thanks for any suggestions! I'm dying here. I just tore it down again and put it back together, dropping the temperature back to 210C from my usual 230C to maybe prevent it from burning in there. Layer height is 0.1mm, speed is about 30mm/s, but at least it hasn't seized up yet this time. That's one thing about ABS, even when my best PLA is barely able to extrude at all, the ABS just comes pouring out..

-Dave

 

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Well I put everything back together and left a print running at 210C. I came back after 9 hours or so (24h print) and halfway through one of the parts had popped off the build platform and it was printing air spaghetti. But spaghetti is better than caramelized PLA. I went to try re-printing it using the new raft option and.... my heated bed never got hot. (Presumably the heated bed died mid-print, causing one of the parts to let go of the glass.) So it seems like I have another issue in addition. Will update as I get a chance to uncover things. I haven't noticed any loose or discolored wires anywhere yet, but need to tear things apart more to look closer.

http://www.sadtrombone.com/

(I went to that web page and the ad was for an Ultimaker2. How it mocks me!)

-Dave

 

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Dave -

Ok, I think there are two, maybe three separate issues here.

1) High resistance when pushing the filament by hand is actually pretty normal. In the normal course of printing, the pressures in the head are really high. So that may not be anything to worry about, as such.

2) The bulges on the end of your removed filament are from the bowden tube lifting out of the teflon piece, I suspect, rather then from the teflon lifting up and creating a gap underneath. You need to make sure the bowden is fully seated, and can't lift up and down once the clip is secured. (See, my recommended procedure http://umforum.ultimaker.com/index.php?/topic/4586-can-your-um2-printer-achieve-10mm3s-test-it-here/?p=40399.)

3) The lip on the teflon piece is a common problem. Heat and time can cause the plastic to creep into the nozzle block opening, restricting the filament movement enough to contribute to under-extrusion.

4) Regarding the heated bed... do you get any error messages, or does it just not heat up? Check the wires going into the back of the heated bed (especially the thicker power wires), and also check at the electronics board end. You might also check the connection between the terminal block on the heated bed and the bed itself.

 

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Thanks for your thoughts, I will investigate them all as soon as I get a chance. As for the heated bed, it gives no error, it just never prints, or the advanced option to heat up the build platform isn't able to affect the temperature. No wires seem to be loose but I need to fully tear it apart to get a better look at things.

My Bowden tube doesn't move at all, but I will be careful to try the directions you linked me to.

Thanks again, will report back when I can.

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Thanks again for all the thoughts and PM.

I took off the heated build plate and poked around and saw no signs of blackened wires or loose connections anywhere. It did look like at least one of the screws holding the black rubber piece that attaches the cable to the build plate was loose though. My current theory is that because that was a bit loose it allowed the solder joints on the back of the build plate to cycle and wiggle just enough that one of the solder joints failed. I opened it all up and the surface-mount connector came off, quite possibly due to my handling. One of the solder joints looked different than the others (more shiny and a darker brown color) which may or may not be important. I soldered the connector back down and reassembled and it seems to be working again.

I removed the Bowden tube from the hot end and did my best to make sure it was seated firmly against the teflon (with thumb screws already tightened). I then performed the "HAS-CAP" procedure a couple of times and got a very similar "shoulder" / bump on the filament. I trimmed it and put it back together and used Move Material to do the same thing with the Bowden tube bottomed firmly before adding the clip, and the results seem the same as before. It's almost as though my teflon piece is too short now or something.

I am almost tempted to apply a series of light but recognizable scratches to the end of my Bowden tube and inside the teflon part, so I can look directly on the filament after I pull it out, and the culprit will be the piece that made its imprint on the filament. I'm supposed to have a replacement Bowden and teflon piece coming so hopefully in a few days I can get it fixed either way. Anyway, fun for another night.

 

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Finally an update: I've received my replacement teflon part, and now that I have the two side-by-side I can see just how bad my teflon part had become. I'm attaching a picture showing them both holding a short section of identical silver PLA:

teflon New V Old

Despite the poor quality of my picture, and beyond just the obvious blackened tip of the old part, there is a very striking difference in how closely the parts fit around the filament. The new part actually holds onto the filament slightly here, due only to the slight bow in the filament. The old part is extremely loose, with lots of clearance between it and the filament (it's even more obvious in person). I think this greatly enlarged insulated cavity may be where my filament had been piling up, jamming my hot-end.

At my last hackerspace they had an old Stratasys machine they were trying to salvage, but the equivalent part (called the inlet buffer) was made out of polyimide and one of them was broken. It was ridiculously expensive stuff (McMaster has 1/2" round stock for $54.51 per linear inch!) but we were able to find some small blocks of it on eBay for cheap and I was able to make a few copies using my lathe and CNC mill (which of course I no longer have..). The polyimide was harder and more brittle than teflon but it machined pretty well. Teflon was kicked around as an alternative but it was deemed that the temperature ratings weren't high enough, at least for the Stratasys (IIRC their head temp was more like 270 or 275C?). Wikipedia is saying that the pyrolysis of teflon is detectable at 200C, suggesting that eventually all of our teflon parts will probably need to be replaced. Given this it seems like investigating alternative materials would be a good idea.

Currently I'm printing with the new teflon part at 50mm/s and 0.1mm layer thickness. I think I may have heard a few occasional pops of under-extrusion but I wasn't paying close enough attention to say for sure that they weren't just the bed dropping for the next layer (they're very different sounds but sometimes if I'm not paying attention I can't swear whether I heard one or the other). I forgot to do Illuminarti's cylinder test before starting a long print, silly me. This is definitely an improvement over before though, as I had it down to about 20mm/s and it was STILL under-extruding badly at 0.1mm layer height.

I'll post an update if I have any issues or notice anything interesting. I do wonder what I must have been doing to abuse this part so badly compared to others. All I can think of is using ABS and nylon.

-Dave

 

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Another status update: about 2-3 hours into my print I started getting really nasty under-extrusion again (speed 50mm/s, height 0.1mm, temp 230C). I slowed it down to 50% (25 mm/s) and let it run for several layers and the under-extrusion didn't stop (feeder stepper kept skipping steps). I did notice that it seemed to lose steps around one particular area that had several retractions, so I lowered my retraction speed from 35 to 25 and distance from 5.5 to 4.5. I then bumped the speed up to 75% (37.5mm/s) and let it go a few layers, and it still seemed good.

I had to abort the print so I figured that was a good opportunity to try Illuminarti's cylinder test. The feeder skipped 4 different times during the bottom 3mm/s band. Looks like it's back to the drawing board.

So let's see what's left... I can tear it down again, take the nozzle off and thoroughly clean it out with acetone (ugh, I HATE taking the nozzle off). Replace the bowden tube. Anything else? I'm running out of ideas. I probably ought to print out something to help make pulling filament take less force, though the under-extrusion was still happening despite me manually providing excess filament.

Can we get Cura changed so that when you hit "Abort" it doesn't retract the filament a huge amount and then forget to ever re-feed it? Every time I need to abort a print (which is frequently these days) I have to either manually "Move Material" afterwards to undo what it did, or (what I often do as it is much faster) I just power the machine off mid-print and lower the build plate manually.

-Dave

 

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The printer shouldn't do a huge retraction at the end of a print. There was a bug in the firmware for a few weeks around the start of this year that did that sometimes, but it was fixed pretty quickly. You should get a 20mm retraction, but if you are getting more than that, then you should update the firmware to the latest version.

What's the material that you are printing Dave? You mentioned feeling resistance getting it to pass through even the new teflon piece... that makes me think that there's a very, very tight radius of curvature on the filament? Is it getting down towards the end of the reel? Forcing tightly curved plastic through the Bowden tube can be really tough. Even if it isn't having to pull it off the reel, just the natural curl in the plastic can be enough to increase the friction. So i'd definitely try straightening out the filament some and see if it behaves better. You can also just try pushing it through your old Bowden tube, and get a feel for how easy (or not) it is to move it (when the tube is bent into a radius approximating the curve when in use).

 

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I see. I've been using the latest firmware, and 20mm sounds about like what it's doing. Until I replaced my teflon piece today, 20mm retraction would be a "huge amount" and result in an immediate jam if allowed to cool that way. Now I realize that my teflon part was almost certainly the culprit of that particular symptom, allowing the large bump to form internally which then can't be effectively drawn back through the bowden or pushed through the extruder.

The material I'm printing is silver PLA, slightly under-sized and in the past it has printed very well for me. I am down past the halfway mark on my spool so it does have a bit of a tighter radius than it did to begin with. I did have a nasty issue with some black filament a while back and had to straighten it out, which helped some, but I think I had a couple of other issues going on as well. It doesn't take a lot of force to push the filament in or out of my bowden tube, I did that a few times this morning during the teardown and it's often how I load material. I will try straightening the filament on the next print. I'm currently about 10 hours in, and there was a little bit of under-extrusion several hours into it in one area, nothing like before but still an issue.

After this print I'll try swapping out the bowden, straightening the filament, and cobbling together some way of more easily feeding off the spool. Thanks once again for all your input.

 

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ALL RIGHT!!! Ok, I am tentatively saying this is solved.

I installed a new bowden tube, new heater block and nozzle (the old ones had totally seized up solid and broke while trying to disassemble it to clean it), and straightened out the filament. I was able to print one of Illuminarti's cylinders completely. I had my finger dragging slightly on the end of the knurled wheel so that I would immediately feel any pops of under-extrusion, and there wasn't a single one. Beautiful! Now if I can just get it to stay that way!

Thanks once again Illuminarti!

-Dave

 

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