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Constant under extrusion with PLA


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Posted · Constant under extrusion with PLA

Ok boys and girls, here is my story:

I am having serious problems with under extrusion when printing PLA on my UM2. This is what I can remember doing to/with the printer since I got it around 9 months ago:

Printer arrived with 1 reel of silver PLA from UM.

I used this material exclusively on the printer with no problems until it ran out.

I then tried some Verbatim 2.85 PLA. This worked a few times but eventually the feeder kept grinding into the filament, which prevented it from working.

I then switched to some ABS I had lying around (not sure which brand), which worked better. Eventually the nozzle became blocked and nothing would come out. This is when I discovered the Atomic cleaning method.

I tried the Atomic method a few times with both PLA and ABS but could never replicate the results shown online. The ABS would always just snap off around the level of the teflon coupler while the PLA would come out stringy rather than nozzle shaped. I did not appear to removing a whole lot of dirt from inside the nozzle either.

Eventually I found some 0.28 wire and used this along with the Atomic method, which made a bit of a difference.

I then tried some new UM 2.85 PLA but was getting very bad under extrusion.

I then switched to some Reprapper 2.85 ABS, which worked a bit better, but eventually the under extrusion came back.

Eventually the nozzle completely clogged again so I decided to disassemble and clean it.

Unfortunately, when removing the setscrew holding the temp sensor in place, it sheared off and trapped the temp sensor. This then broke when I pulled it out.

UM sent me a new nozzle kit, which I reassembled into the printer.

I started printing with the Reprapper 2.85 ABS and this worked great up until now.

Recently the nozzle became blocked again so I used the Atomic method a few times with ABS, then tried the Atomic method with PLA a few times before trying to run some PLA.

I had to use my 0.28mm wire again a few times before all the old ABS would come out and could finally start printing with the PLA.

So this is the first time printing with UM 2.85 PLA since replacing the nozzle but I am getting exactly the same under extrusion problems as before!

I have since used the Atomic method a few times with the PLA before switching back to the Reprapper ABS and it is printing fine. But I really want to be using PLA!!!

I cannot for the life of me work out why this is happening. My next step will be to disassemble the nozzle again to check for dirt but I don't understand why the first PLA worked best of all the materials and now I cannot print PLA at all.

To summarise:

UM PLA worked great

Verbatim PLA under extruded

Random ABS worked

Eventually random ABS under extruded

Used the Atomic method

UM PLA under extruded

Reprapper ABS under extruded

Eventually nozzle became blocked

Replaced nozzle

Reprapper ABS worked

Eventually Reprapper ABS clogged nozzle

Used the Atomic method

UM PLA still under extruding

Reprapper ABS working fine

For printing PLA I use the default settings (210 nozzle, 60 bed, 50% fans). I tried +/-10 degrees nozzle temperature on a few prints but this made little difference.

Before replacing the nozzle I used default ABS settings (260 nozzle, 90 bed, 50% fans). Just before changing the nozzle I changed the settings to 250 nozzle, 110 bed, 0% fans, which gives a good result for me.

I have checked all of my filaments and they are definitely closer to 2.85mm than 3.00mm. The only other thing is that when the PLA under extrudes, the feeder grinds it down and you can see filament dust being pulled into the Bowden tube. However, I do often blow some compressed air through the Bowden tube to clean it when messing around with changing materials.

Any help on the matter would be greatly appreciated,


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    Posted · Constant under extrusion with PLA

    There are sooo many causes of underextrusion. Here are 2 of them - the white teflon part degrades pretty quickly at temps above 240C so it may be time to change out that part. People who switch from ABS to PLA in particular have this problem plus bits of ABS dust showing up in the nozzle.

    Another thing is that you replaced the temp sensor. If the sensor is loose it tends to read low and so the nozzle is hotter than normal (as much as 20C). If the sensor is tight the nozzle can be as much as 10C cooler than normal. While it's underextruding I would go into the tune menu and go as high as 240C (not just 220C) but don't go over 240C for PLA.

    Another thought is that if I print ABS at 260C I get clogs incredibly easy - especially if I print too slow or let it sit like that without printing for a minute. ABS just tends to bake into a gummy gunk very quickly and easily.

    I'd like to see some closeup photos of underextruded parts please.

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    Posted · Constant under extrusion with PLA

    Thanks for the reply. In response:

    The Teflon coupler was replaced along with nozzle when I installed the new kit. Even then, the previous Teflon coupler had probably been used for <100 hours.

    I made sure the temp sensor was tight enough when I installed it, but I will check this again if/when I disassemble it again.

    Since replacing the nozzle I have not printed ABS above 250C.

    Here are some recent photos. The first is the test piece I printed after changing over to PLA in the new nozzle. This is after using ABS and performing two Atomic pulls in ABS, two Atomic pulls in PLA and bit of wire wriggling to clear the nozzle. As you can see it completed it but the surface finish is not great:


    Here is the next piece in PLA with epic under extrusion for no obvious reason:


    Here is the exact same part printed in ABS (this is after two Atomic pulls in PLA before inserting the ABS):





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    Posted · Constant under extrusion with PLA

    Please read through my standard list below. Especially #1. I recommend the IRobertI feeder because it can help you narrow down the causes because you can feel the pressure by hand by simply opening the feeder and pushing on the filament and seeing how much is coming out.

    I also recomend the Olsson block from 3dsolex because you can test #2 and #6 more easily by removing the nozzle and feeling the friction through everything but the nozzle with the heat off. A valuable diagnostic. Also you can have one nozzle for ABS and one for PLA as it's just problematic switching back and forth. Also you can swap nozzles to see if that makes a difference (and you can burn one nozzle out with flame or soak in acetone while printing with the other).


    As far as underextrusion causes - there's just so damn many. none of the issues seem to cause more than 20% of problems so you need to know the top 5 issues to cover 75% of the possibilities and 1/4 people still won't have the right issue. Some of the top issues:

    1) Print slower and hotter! Here are top recommended speeds for .2mm layers (twice as fast for .1mm layers):

    20mm/sec at 200C

    30mm/sec at 210C

    40mm/sec at 225C

    50mm/sec at 240C

    The printer can do double these speeds but with huge difficulty and usually with a loss in part quality due to underextrusion. Different colors print best at quite different temperatures and due to imperfect temp sensors, some printers print 10C cool so use these values as an initial starting guideline and if you are still underextruding try raising the temp. But don't go over 240C with PLA.

    2) Isolator - this is most common if you've printed extra hot (>240C) for a few hours or regular temps (220C) for 500 hours. It warps. It's the white part touching the heater block. Test it by removing it and passing filament though it by hand.

    3) Curved filament at end of spool - if you are past half way on spool, try a fresh spool as a test.

    4) curved angle feeding into feeder - put the filament on the floor -makes a MASSIVE difference.

    5) Head too tight? Bizarrely MANY people loosen the 4 screws on the head by just a bit maybe 1/2 mm and suddenly they can print just fine! Has to do with pressure on the white teflon isolator.

    5b) Bowden pushing too hard - for the same reason you don't want the bowden pushing too hard on the isolator.

    5c) Spring pushing too hard. Although you want a gap you want as small as possible a gap between teflon isolator and steel isolator nut such that the spring is compressed as little as possible.

    6) clogged nozzle - the number one problem of course - even if it seems clear. There can be build up on the inside of the nozzle that only burning with a flame can turn to ash and remove. Sometimes a grain of sand gets in there but that's more obvious (it just won't print). Atomic method (cold pull) helps but occasionally you need to remove the entire heater block/nozzle assembly and use flame.

    7) Temp Sensor bad - even the good ones vary by +/- 5C and bad ones can be any amount off - they usually read high and a working sensor can fail high slowly over time. Meaning the sensor thinks you are at 220C but actually you are at 170C. At 170C the plastic is so viscous it can barely get out of the nozzle. You can verify your temp sensor using this simple video at youtube - on you tube search for this: mrZbX-SfftU

    8) feeder spring issues - too tight, too loose

    9) Other feeder issues, one of the nuts holding machine together often interferes with the feeder motor tilting it enough so that it still works but not very well. Other things that tilt the feeder motor, sleeve misaligned so it doesn't get a good grip. Gunk clogging the mechanism in there.

    10) Filament diameter too big - 3mm is too much. 3mm filament is usually 2.85mm nominal or sometimes 2.9mm +/- .05. But some manufacturers (especially in china) make true 3.0mm filament with a tolerance of .1mm which is useless in an Ultimaker. It will print for a few meters and then clog so tight in the bowden you will have to remove the bowden from both ends to get the filament out. Throw that filament in the trash! It will save you weeks of pain

    10b) Something wedged in with the filament. I was setting up 5 printers at once and ran filament change on all of them. One was slowly moving the filament through the tube and was almost to the head when I pushed the button and it sped up and ground the filament badly. I didn't think it was a problem and went ahead and printed something but there was a ground up spot followed by a flap of filament that got jammed in the bowden tube.

    11) Hot weather. If air is above 30C or even possibly 25C, the air temperature combined with the extruder temperature can soften the filament inside the feeder such that it is getting squeezed flat as it passes through the feeder - this is obvious as you can see the problem in the bowden. The fix is to add a desk fan blowing on the back of the printer.

    12) Crimped bowden. At least one person had an issue where the bowden was crimped a bit too much at the feeder and although the printer worked fine when new it eventually got worse and had underextrusion on random layers. it's easy to pull the bowden out of the feeder end and examine it.

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    Posted · Constant under extrusion with PLA

    You need to tackle this through a process of elimination.

    So, if ABS is fine and PLA is not, there is clearly no issue here other than the nozzle. Feed 20cm or so of PLA through at 240C and that should help clear out any ABS up quite nicely. Make sure you run the PLA through really quickly, otherwise you will get a bigger mess on your hands than you want. You could always print some random object at 60 mms/s and 0.2mm layer height, which will be shoving plastic through at a fast clip, and although 240C is a little high for PLA even at that speed, it should not burn.

    For the record, I switch between PLA, ABS and nylon regularly so it's quite a normal thing to do.

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    • 2 weeks later...
    Posted · Constant under extrusion with PLA

    Ok well I will be working through your list gr5, thanks.  I had it in mind already to buy a set of those nozzles.  I have managed to print out the alternate feeder as well but it probably won't be until after Christmas that I will be able to effect these changes.  Will give an update then.

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