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kirash4

Printing with PLA - no luck

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I'm having one heck of a time printing with PLA on my UM2. I can print ABS all day long, no problem what so ever. Different settings, different object, stopping, starting, no issues at all. PLA on the other hand ... no can do.

Whenever I put in PLA material, select the PLA setting on the printer and start a print, it would start but within a few layers the nozzle will clog up and it'll stop extruding. I'll abort the print, heat up the nozzle to what would be the ABS temperature and push material through. I'll get this black crud coming out for a while before it finally starts flowing again. That tells me it's getting clogged and burning the material in the nozzle. So I can clean it all out and try again. It'll do a few layers again before quitting. Lather, rinse, repeat.

I can switch back to ABS, and voila, no problems what so ever. So I took a closer look when I tried again tonight and something caught my eye. The Bowden tube has bits and pieces of ABS in it. This then make me wonder if that's what is happening. It gets pulled in with the PLA, and since the nozzle is at a lower temperature (for PLA), the ABS won't melt and therefor clog up the nozzle. And when I raise the temperature it unclogs, pushes the melted ABS out and the now burned PLA as well.

I'm literally grabbing in the dark here, this is the only thing I can think of that's going on. And if that's the case, how do I clean out the Bowden tube whenever I want to switch to PLA?

If anyone else has other ideas of what may be going on, or why it's constantly failing, I'm listening.

 

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Hi and welcome to the forum.

To clean the bowden tube you have to unlock it a both ends (the head and the feeder).

To unlock take out the blue clip (carefull not to loose it) then push down the white collet to release the bowden then pull the bowden. No force is required.

Do this with filament unloaded of course :)

Then use a piece of filament and push it in the released bowden to make your residues come out.

Other than that when going from ABS to PLA is always a good idea to clean the nozzle. Use the atomic method described here:

http://support.3dverkstan.se/article/10-the

Do it several times to be sure to have a clean nozzle, some ABS residues will clog the nozzle at PLA temperature.

PLA is easier to print than ABS so you will sort it out ;)

 

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PLA is easier than ABS ... Yeah, that's what everyone has been telling me, except I have never been able to print with PLA. I can load up ABS and print just fine. But no such luck with PLA ... Must be me. It always seems to get two, maybe three layers out then it clogs. Blah.

Anyway, I just cleaned the tube, reassembled everything, no more white bits in the tube. Tried a print and sure enough it clogs again. Usually I can tell when I start hearing the feeder gear start slipping and it gets worse and worse to where it's constantly slipping and nothing is being extruded anymore. But if I try pushing on the filament (to help the feeder), out comes this black crud again.

Why would it start just fine and slowly get worse and clog? Is the temperature too low? Is it too high? I started with the stock profile which has the nozzle temperature at 210C. It barely extruded anything. I'm slowly raising the temperature but I don't know if that's the correct course of action here. I honestly have no idea what else to check.

 

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Switched back to ABS, and it's printing just fine. No issues what so ever. I've now tried different brands of PLA as well and they all do the same exact thing. I'm more likely to blame the printer than the material. If it was all from the same vendor or brand I can see a problem there, but with different brands and it still fails, something's up.

For the record, I made sure it has the latest firmware on it, recently downloaded from Cura (the latest that's online.) I did a factory restore to see if I screwed up the settings somewhere. Nothing. It simply will not print PLA. Unfortunately, the translucent that I want to use only comes in PLA. So I would really, really like to be able to print with this material.

 

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You tried different brands of PLA but have you tried the ultimaker brand? they all come in different diameters! I have several colour pla here and no problem with printing! Only once did I get a nozzle blockage and that was when changing from abs to pla.

When you change filament, after the machine retracts the old filament, there is often a very fine thread of filament left in the bowden tube, You can often see the end of this thread at the knurled driving gear, its easy to extract using a piece of wire with a tiny hook on the end.

 

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When you switch from ABS to PLA, most likely you have some ABS residue left in the nozzle. I usually do a 2 hour print with PLA on ABS settings after switching to PLA to clean out the nozzle. (The print won't be pretty, but it will take all the residue that otherwise clogs the nozzle with it)

 

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You might want to tear the head apart and look at the insulator. I find that if the machine will print ABS fine but fails with PLA, it's usually becasue the insulator is worn. ABS seems to be a lot more forgiving with a worn insulator than PLA.

This is assuming it is absolutely not a blockage problem.

 

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You might want to tear the head apart and look at the insulator. I find that if the machine will print ABS fine but fails with PLA, it's usually becasue the insulator is worn. ABS seems to be a lot more forgiving with a worn insulator than PLA.

This is assuming it is absolutely not a blockage problem.

 

I just wanted to echo this. For a long time I had a worn isolator and I spent a lot of time looking at the wrong things. ABS was the only thing I could print. When I finally realized it and got a new isolator, it was a whole new machine.

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@korneel: stock feeder

So I finally had a moment to tear the head apart and pull the coupler out. It's not pretty.ptfe.jpg

That's the bottom part that sits right ontop of the hot end. I suspect it was sitting low enough to be in physical contact with it and got burned to what you're seeing. Lots of burnt crud and what not came out.

So I'm now stuck. I need another one, like yesterday. I don't think I can continue printing with this the way it is, well maybe ABS but I need to get some PLA prints done ASAP as well.

Does anyone have suggestions on where I can get another one, quick, fast, and in a hurry? Or what I can do in the mean time other than twiddling my thumbs waiting for a replacement?

 

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Mine turned out like that so I sanded the bottom so it was nice and flat and re drilled the hole. Months later it's still going strong. If you don't have the correct size drill bit (3.2mm by memory, but u should check) then you can get a sharp pointed knife and remove the lip on the inside edge.

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Hmm, yes, I suppose. I did clean up all the charred bits by gently scraping them off with an Xacto knife. The hole seems okay other than some scarring on the inside, but I can still slide a piece of filament through it without any resistance. I ended up sanding the outside because it flared out a little bit, making it a bit harder to put back inside of the insulator coupler. I didn't screw the coupler all the way back on, which basically pushes the nozzle out more, leaving a bit of a gap between the backside of the nozzle and the insulator. Once I did that and reassambled it, it's printing PLA right now. Still fiddling with speed and temperature but it things are looking up.

I'm still going to order a replacement of course, in fact, two of them. Which brings me to my next question: is there a guide somewhere that explains how to properly put everything back together? I'm mainly interested in how far down should I be screwing the coupler that holds the nozzle in place? If I go all the way in, then the back of the nozzle touches the insulator, which is why I left it unscrewed a bit. But what's too much or too little? When I look at the assembly manual, it just says to turn the coupler till there's a 1mm gap between the coupler and the insulator and the coupler is "just not touching" the hot end. Well, that's where it was when all these problems started. So I've left it unscrewed more so it's further away from the hot end. So far so good, I've run several 20minute PLA prints through. About to try an hour long one to see what happens. Also, the pieces I'm printing with PLA are rather thin, only 5mm in height. Should I expect problems if I start printing something that's way taller than that, say 200mm?

 

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Yeah, disassembly is easy, I got that part. Reassembly is what I'm looking for. Specifically the tolerances between the ring holding the heater block and the block itself. Mind you, it's working great right now ... but that doesn't necessarily mean it's done correctly. :)

 

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Yeah, disassembly is easy, I got that part. Reassembly is what I'm looking for. Specifically the tolerances between the ring holding the heater block and the block itself. Mind you, it's working great right now ... but that doesn't necessarily mean it's done correctly. :)

 

I think this is what you're looking for. Check post #20 for the correct nozzle assembly.

http://umforum.ultimaker.com/index.php?/topic/8513-underextrusion-need-help-with-this-one/&do=findComment&comment=80503

 

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Yep, I found that thread too. I haven't had to touch it in a few days because I'm back to printing ABS which works great, though I attribute that to the higher temperatures. I'm going to have to switch back to PLA shortly here (possibly as soon as tomorrow) and my nightmares will start up again. Technically I shouldn't go past 230C with PLA, but the last batch of PLA prints I did I was working at 240C with 94% extrusion (going any higher and the PLA starts to turn into something completely different.) It's simply not extruding as it should, or as well as the ABS is. So setting (or leaving) the feeder at 100% causes it to constantly skip (even at full tension) and every time it slips, I lose what little pressure there is in the nozzle which results in gaps in the print. But it's working at the aforementioned settings. So I'm going with it for now till I can replace both the insulator and the nozzle itself. It's seen its fair share of isues in the few months that this printer has been in service. I think it's time to scrap it and start with a new one.

 

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I've run several miles of filament through my UM2's now....

When I have a problem, and change my Insulator and nozzle , it's like a new machine. I have changed the bowden tube ONCE on each, and I do use the torch method to clean the nozzles, so I'm not in the same boat as everyone, but if you are willing to torch the nozzle, replace the insulator, and periodically clean the bowden tube, then you should be good to go.

The trick is having the spare parts on hand :)

 

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Yeah, and I lack the latter. :) But you are correct, I am highly suspecting the insulator and nozzle at the moment. The main culprit right now is the insulator because I found it to be so badly burned. And while I was able to clean it, resand the bottom flat, and all of that, I did also notice that the inside of it has developed a "ridge" where material tends to solidify and over time will cause friction. So I have to tear it apart after so many hours of printing to clean that out before I can continue again. It's a bit of a hassle but I need to get through these prints right now. By month's end I'll be done and I'll do a thorough cleanup and replacement of parts.

Question, how do you do the "torch method" to clean the nozzle?

 

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- You shouldn't need more than 220-224 with PLA or 235-242 with ABS - any hotter and you will cook the isolator. Running ABS hotter than that will also boil off bad-smelling toxic plasticizer components from the ABS (sometimes visibly), and will give less-than-optimal results. Anyone who tells you they are printing ABS at 260C either has a badly-calibrated temp sensor, or will be frequently replacing the isolator and bitching about it.

- redirect the unused small-fan air toward the isolator to cool it better - there is a thread on how-to do so easily.

- if you are using a relatively new UM2 with the stock feeder, it will grind chunks of black ABS off the entry hole and move them into the Bowden tube, from which they will embed small black pieces of ABS in your prints before clogging the nozzle when printing PLA. Replace the offal (sic) factory feeder with |Robert's| version.

I commonly run two to three day-long prints with both PLA and ABS, and I've got over 2000 printing hours on the original isolator on my UM2.

 

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To torch the nozzle, you have to completely disassemble the head, and remove the nozzle. I always warm up the nozzle before removing the set screw (and thermistor and heating element), and while holding the nozzle with a pair of pliers, unscrew the set screw. You then just use a low temp gas like propane to torch the nozzle (MAP gas will work in a pinch). From there just clean the nozzle of carbon at your discretion, using whatever you have on hand to get it nice and clean.

 

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