Filament building up on back of hotend



  • Duet 3, Corexy printer. As I am printing I am getting a ball of filament building up on the back side of the hotend nozzle. Is there a way to calculate or fine tune relative extrusion ? Or what should I print as a test to see what is going on ?



  • Are you printing Petg?



  • I was having a lot of that sort of issue printing PETG. One weird trick (haha got you!) fixed it- I disabled lift on retract and lift on layer change. Prints are much less hairy, and charred blobs of filament stuck to the print are very rare.



  • @baird1fa I am printing PETG 240 and bed at 78


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  • @mrenz999 PETG is just sticky plastic. It works best with coated nozzles like nickel plated or nozzle X. But it really likes to stick to bare brass and do just like you said.

    Another thing is when you print your first layer try not to squish it too much. Too much squish causes it to wrap up a bit around the nozzle and then it builds up like you said.



  • +1 on esteps and flow rate. +1 on not using Z hop.

    Also, watch out for that first layer with PETG. Don't smash it down as hard as you might with other materials. It's best if you make that first layer as high as you can without loosing bed adhesion.

    If your esteps and flow rate are set but you're still getting blobs on the nozzle, just drop the flow rate 1% at a time (try and grab the blob off the nozzle with tweezers when you make each change) and see if it builds up again. Obviously you can go too far and end up with sparse surfaces, but PETG seems to like a bit of under extrusion.

    I use 240 for my first layer, then 230 with 20% fan after that. Seems to work well.



  • @Phaedrux I have and redid again. I have that correct.



  • @baird1fa I use an X nozzle with a volcano.



  • @baird1fa said in Filament building up on back of hotend:

    @mrenz999 PETG is just sticky plastic. It works best with coated nozzles like nickel plated or nozzle X. But it really likes to stick to bare brass and do just like you said.

    Another thing is when you print your first layer try not to squish it too much. Too much squish causes it to wrap up a bit around the nozzle and then it builds up like you said.

    Doesn't work with nozzle-X, PETG builds up on them by the same amount as a normal nozzle, so much so I sent my three I bought back to E3d for a refund.

    PETG doesn't like to be "squished" down like some other filaments play with baby stepping to find the sweet spot.

    I have listed before that I initiate a 0.2mm baby step up at layer 5 which I have found helps both the build up on the nozzle and stops "boogers" forming.

    And with PETG it is VERY important you print a temp tower as depending on the brand it might not print at what the manufacturer list the temp it prints at, as (again already mentioned in the past) I tested a roll of PETG from "Das-Filament" which wouldn't print successfully until i dropped its temp down to around 190c (PLA Temps)


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