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Filament jamming up in head?


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Posted · Filament jamming up in head?

Can anyone explain why the filament keeps jamming in the print head? 

Its happened twice and every time i need to take apart the head to get out the stuck/melted piece!

Im using PLA at 200C temp. 

ultimaker.jpg

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    Posted · Filament jamming up in head?

    Make sure that 3rd fan there (not the side 2 fans but the middle one) is working.  That's a common cause.  If not that then replace the teflon part.  You should change it out every 500 hours or so.  More often if you print hotter than 210C.  Teflon, like filament, is considered a consumable.

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    Posted · Filament jamming up in head?

    There is not one answer but normally the teflon gets soft after a few hundred hours above 180C and with the compression (from the bowden pushing down, from the aluminum cylincer spacer pushing down) it squeezes the filament - mostly right where it enters the brass heater block.  This pinches the filament and makes it difficult to feed and can cause underextrusion.  Also it's possible for the filament to cool after a print and it can't come out of the printer past that skinny spot of the teflon.  Or sometimes you can't get filament to insert past that skinny spot.

     

    I'd replace the teflon and you could potentially save the old one and this doesn't fix anything mark the old one as "good".

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    Posted · Filament jamming up in head?

    Looking again at the photo.  Is it possible your bowden wasn't all the way down?  The bowden needs to pass all the way through the aluminum cylinder and then a little farther into the teflon part.  There is a ridge and if the bowden isn't centered then there will be a gap where the filament (if too warm) can expand into that space just above the teflon and below the bowden.  This shouldn't normally happen as the filament should be cool enough above the teflon to be solid.  But if you have a hot environment due to your building or due to weather the PLA might take a little too long to cool and it can smoosh out/expand into that gap.

     

    The fix is to make sure the bowden is all the way down.  I have a 3d printed replacement for that aluminum that has a slit in the side so you can see what's going on inside.  You have to print it in ABS though.

    https://www.youmagine.com/designs/um2-spring-replacement

     

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    Posted · Filament jamming up in head?

    Thanks for the info! 

    It looks like i keep getting failed parts. I believe im putting the tube all the way in and the printer is set up fine to begin. Maybe its the teflon that is the issue? The problem looks to be stemming from the print head jamming, which then causes the the feeder to chew up the filament. Heres some images of the latest filament that i pulled out of the print head and the failed part. 

    failed-part.jpg

    failedpart2.jpg

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    Posted · Filament jamming up in head?

    Yeah.  Teflon.  That final picture is helpful.  Also - are you sure that 3rd fan is working?  stick a piece of paper in there 3 times during your print to hear the paper buzz.  Or stop the fan with your finger to know what to listen for.

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    Posted · Filament jamming up in head?

    What is the air temp in your room?  Is it like 25C (too hot!)?

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    Posted · Filament jamming up in head?

    3rd fan is def working. I have an air filter enclosure around the printer, its a clear acrylic door and top covering with an air filter. So maybe the temp is a bit higher inside the printer but my place is not hot, 72° temp.

     

    I was printing usual settings with 0.25 nozzle before. I just switched back to 0.4 and its working ok now. If i see jamming again, I will get some new teflon.

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    Posted · Filament jamming up in head?

    If you have this only with a 0.25mm nozzle, but not with a 0.4mm nozzle, maybe you are printing too hot for it, and the heat still creeps up into the filament due to not enough filament flow? Or the filament begins to decompose?

     

    If you do a cold pull (atomic pull), the tip should look like the orange one at the very bottom here (minus the color-change, this was when changing colors, to clean the nozzle). If it looks like the white one, with a thick ring or blob where the teflon meets the metal part of the nozzle, then the teflon is definitely worn-out.

     

    Also, it could be that the bearings of the little fan are worn-out, so that it is still running, but way too slow to generate enough airflow? If it makes rough sounds like "rheu-rheu-rheu" then it is for sure worn-out. Or maybe there are hairs stuck in it, reducing speed and flow? Airflow goes with a power of RPM, not linearly, so a small reduction in RPM gives a huge reduction in airflow. When looking at your pictures, I still have the idea that the third fan's cooling is not sufficient, and heat is creeping up, melting the filament before it reaches the nozzle, as gr5 said.

     

    DSCN5237.thumb.JPG.8f29c03aad2ce9dd0d9490ed2ece9d98.JPG

     

    DSCN5238.thumb.JPG.c0b3c52c2588d4c4a95ec6ac24bd3e99.JPG

     

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    Posted · Filament jamming up in head?
    8 hours ago, mike_churchill said:

    3rd fan is def working. I have an air filter enclosure around the printer, its a clear acrylic door and top covering with an air filter. So maybe the temp is a bit higher inside the printer but my place is not hot, 72° temp.

     

    I was printing usual settings with 0.25 nozzle before. I just switched back to 0.4 and its working ok now. If i see jamming again, I will get some new teflon.

    Oh!!  That changes everything.  Do you have one of those $10 IR temp guns?  point it at the back of the printer and let us know the air temp if you can.

     

    Yeah don't use an enclosure with PLA.  It's hard enough to keep things cool with the side fans at full blast but a top cover and a heated bed can result in air temps around 100F which is just too hot for a UM2 series printer.  I mean that's great for printing higher temp materials but not for PLA which gets soft at 52C (130F).  Inside the teflon part and I think even just above you are seeing temps above 52C and that is causing the problems.

     

    You could lower the temp.  I like to print much cooler (180C) when printing 0.25mm nozzle.  And limit retractions.  And try to get more cooling.  .25mm nozzle is tricky - like geert says, the slower printing volume causes problems as you aren't feeding nice cool filament at the same rate as with e 0.4mm nozzle.  Typically 4X slower (volume of PLA - not print head speed). 

     

    Also doing thick(ish) layers is good.  I'd do 0.1mm layers.  People often want to scale down the layer height when they scale down the line width but that's a bad idea in your case.  Thicker layers will increase the volume per second of PLA which helps to keep things cooler in the upper part of the hot end (where your problem seems to be).

     

    COVERS

     

    Why the cover and air filter?  That's fine for ABS but you don't need it for PLA.  Did some article scare you about particles in the air?  I'm pretty sure PLA is relatively safe.  If you read all those reports about PLA particulates carefully you will see that the original research also mentioned that candles, bacon, burger frying and french fries all create very similar particles in much higher concentrations. 

     

    So worry about breathing the air in a McDonalds or burning a candle in your home or frying bacon in your home long before you worry about a few printers printing PLA.  Don't get me wrong - ABS is nasty.  And ABS will benefit from the higher temps that a cover will create.  ABS doesn't get soft at 52C like PLA.  It gets soft at 99C and you can even pour boiling water into an ABS cup and it's fine.  Not PLA, lol.

     

    News agencies only make money if you read their articles so they tend to be scary: "Is your 3D printer creating dangerous particles?"  Then you read the details of the article and it's like "Okay so each printer is like one candle?  Pfft."

     

     

     

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    Posted · Filament jamming up in head?

    Great insights! I imagine the problem is the temp creeping up with the enclosure. Ill need to lower the temp and check it with one of those IR guns (i dont have one yet). 

    Im also using the enclosure because, yes, i was scared into the idea of particles LOL. But also because it helps with the smell. The filter removes most of the smell so its nice to not have that oder lingering around. 

     

    Quote

    "Okay so each printer is like one candle?  Pfft." 

    haha this is great! Makes sense 😆

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    Posted · Filament jamming up in head?

    So in short - you are using the printer beyond it's expected abilities.  Add a fan to your filter or just get rid of the cover.  Or don't print PLA (but PLA is the easiest and the best material).  That cover is bad for PLA but won't hurt if you are printing PETG and is actually helpful for Nylon (but now you are printing too hot and the teflon part in the print head won't last nearly as long).  Ideally stick with PLA and remove the cover but if you really want the cover then add a fan to the filter.

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