Why does my PLA filament form a spiral shape and clog my extruder?

  • Why does my PLA filament form a spiral shape and clog my extruder? Curtis

    I'm using brand new PLA filament and am getting frequent clogs in my extruder.

    I've had this problem with 2 different filaments from 2 different vendors.

    It will be print just fine, then clog up. It doesn't ever seem to go more than 5 minutes before clogging. When it clogs, and I pull out the filament, it is always twisted in a spiral (helix) shape like a corkscrew. I have put a picture of 2 clogs below.

    I have tried using temperature of 220 all the way down to 180 in increments of 5 degrees and seem to get the same result. it prints the base layer GREAT on the 70 degree heated bed. No warping or peeling off. However, after a few layers, it clogs up and stops extruding.

    I am using an HIC PRUSA I3 printer with a single extruder head. I've only had the printer for a couple weeks. It had been printing fine with ABS, but the ABS would peel up from the heated bed, so somebody suggested that I use PLA and hairspray. Hairspray is AWESOME !! It sticks really well and removes easily as well (once the bed cools a bit).

    Please let me know if you've had the same problem with the extruder just clogging up and twisting the filament into a corkscrew shape.

    By the way, pay no attention to the black marks on the green filament below. That's just me marking every half inch or so with a sharpie marker to see if it's still being extruded.

    Filament Helix

    I think I figured out the problem. Now, to figure out a solution... Take a look at the image below. There is a 1 inch tube that goes from the heat element to the heat sink. This 1 inch of tubing is REALLY hot and larger than 1.75mm. So, the filament goes through that tube on its way to the head and gets soft in the tube because the tube is so hot all the way down to the head. When the filament gets hot, it melts and bends and curls which makes it NOT push itself into the heated tip and out onto whatever I'm printing.

    The solution would be to find some way to cool this 1 inch shaft between the heat sink and the heated head so that the filament inside of it won't melt.

    Any ideas???

    Extruder Assembly

    Here is a picture of my heat tip. Note the shaft has about 1 inch sticking out of the heater. The top of that (above the white arrow) is inside the heat sink. But 3/4 inches of it are bare and uncovered. There is also no teflon tube inside the metal throat.

    enter image description here

    Another picture of the extruder

  • The shape you get is quite easy to explain. It's the shape of the lowest energy possible in your situation. Simple but it doesn't explain the issue... or does it?

    It does. The filament cannot be put into the extruder as it becomes plugged. This leads us to some obvious explanations. You can read this post.

    So how is that possible that there is enough room to form such corkscrew? My bet is you don't have teflon pipe inside the extruder heatsink. So filament goes into the heatsink and everything is ok until the heatsink itself warms up to the temperature when filament becomes soft, then there is no enough force to push the filament out of the nozzle so above the nozzle filament bends and forms the shape of the lowest energy as said.

    Options to check:

    1. Take your extruder apart. See if there is a teflon pipe. If its length is proper.
    2. Check if cooling fan is working well, if it's pushing air to the heatsing but not sucks from the heatsink.


    Looking closer to your photos I'm pretty sure you don't have such teflon pipe. Your spiral has flat external (virtual) surface... it looks exactly as it would be pushed into hot pipe with diameter of 4mm.

    [edit2] please take a look on the picture enter image description here

  • The distance between heat block and heat sink is too big (3/4 inch, almost 2 cm). In this area your filament is some half melt state, not cooled as in heat sink part, not melted as in heat block part. You should make as small as possible, less then 0.5 cm.

    Great source of information about hot ends is video created by Thomas Sanladerer: Build your own 3D Printer: Which hotend to pick!

filament extruder prusa-i3 pla
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