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  1. #1
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    Post removing filament always jams extruder (Anycubic Mega-S)

    Hey y'all. Thanks ahead of time for your insights!

    I'm printing PLA on an Anycubic Mega-S, and every time I go to remove the filament for a color swap, it jams in the extruder. Even with the release lever engaged, the filament jams because the end of it melts into a small "blob" that's wider than the diameter of the filament itself. I've tried heating up the hot end in order to feed in the filament and melt the tip a little before pulling it out, and that doesn't seem to help much. Any suggestions? I'm afraid I'm just going to break the extruder if I just keep forcing it out.

    Thank you!

  2. #2
    Engineer-in-Training
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    I'm not one hundred percent familiar with the model you have, but the problem is not an unusual one, especially if you have a hot end which uses a bowden tube of any length inside the heat sink. If you have a bowden tube, push the release fitting and pull it out while the nozzle is at the right temperature for your filament. You'll want to ensure that the cavity is clear of filament and re-insert the bowden tube until it bottoms out. Perhaps if you can, replace the tube, or cut it back to remove the "teeth marks" left by the release fitting.

    If the tube is not pushed all the way in, the blob will form on a regular basis and may eventually jam without a filament swap. Another thing to consider is when you are removing the filament, extrude a few millimeters before you retract, which of course requires that the nozzle be at the correct temperature.

    Even direct drive systems have a bit of PTFE tube, so ensure that yours is fully inserted. Use a toothpick or similar item to locate the depth at which the throat changes diameter and match it to the amount of PTFE tube that is inserted.

  3. #3
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    Thank you, fred. So just to make sure that I'm understanding you correctly, all of the adjustments you're describing are in the print head assembly, right? So I have to take that apart to see?

  4. #4
    Engineer-in-Training
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    I've pulled the manual up on the web site and page 15, figure 5 shows a zip tie around the release fitting for the bowden tube. This confirms that your printer is not a direct drive and confirms that the efforts should be focused in the area of figure 5. If you've accidentally removed the zip tie, there's a good chance the problem is related to that. If not, get a spare zip tie and cut off the one in the photo.

    Once you've cut the zip, push the fitting downward while pulling upward on the PTFE tubing. It's going to be easier if you've removed any filament you can, perhaps even easier if you've heated the nozzle up to temperature. That may be your best bet, as you really want to remove any filament that's been "bulbed" under the PTFE tubing.



    Disregard the circled area in the image above. It's not related to your problem, I hope.

    Instead, focus your attention to the colored area around the blue at the top of the image. I'm color blind and not sure if it's yellow or green, but you get the idea. Notice that the bottom of that color (the PTFE tube) is as far into the recess as it can go. If your PTFE tube is not bottomed out, there's a gap that creates the problem you've described. By heating up the system before you try to pull the PTFE tube clear, you may be able to get the bulb out if it is there. I'm hopeful that you don't have one at all, as I don't know how you'd get that out other than by disassembly and replacement of the heat break. They aren't particularly expensive if you don't buy the thirty dollar titanium version, but it's an inconvenient task at the very best.

    Once you have the PTFT tube out, fish around with a skewer or similar non-metal object to determine the depth of that bore. You want to have a good idea how far you have to push in the PTFE tube on the re-assembly portion.

    As far as your question about taking things apart, this is indeed doing so, but it's a "surface" operation, not digging deep into the guts.

  5. #5
    Student 686 Shooter's Avatar
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    On my Mega S the bowden tube was not tight against the nozzle. This will contribute to your problem. Also the tube itself is not of great quality, I replaced mine with some Capricorn tubing.

    To ensure your bowden tube is tightly sealed against the heat break heat the hot end to 200 degrees, loosen the tube fitting on the top of the hot end by 3/4 to 1 turn. Push the tube in until you are sure the tube is touching the heat break then tighten the fitting. This will give you a nice compressed seal and avoid any leaks. This solved the problem for me.

    I also found that it helped to push the filament into the hot end until you get some coming out then quickly pull the filament back.
    Last edited by 686 Shooter; 04-05-2020 at 02:40 PM.

  6. #6
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    I have an old CTC and found removing the old filament less than perfect. I always snip the filament off and just keep extruding it and then feed the next
    filament in as it runs out. Wait for the colour change and then its ready to go.

    Saves having to pre-heat also if your ready to print. Less hassles with small stringy bits getting left behind or clogging the feed.

    Does not waste much filament.

  7. #7
    Engineer-in-Training
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    Quote Originally Posted by 686 Shooter View Post
    On my Mega S the bowden tube was not tight against the nozzle. This will contribute to your problem. Also the tube itself is not of great quality, I replaced mine with some Capricorn tubing.

    To ensure your bowden tube is tightly sealed against the nozzle heat the hot end to 200 degrees, loosen the tube fitting on the top of the hot end by 3/4 to 1 turn. Push the tube in until you are sure the tube is touching the nozzle then tighten the fitting. This will give you a nice compressed seal and avoid any leaks. This solved the problem for me.

    I also found that it helped to push the filament into the hot end until you get some coming out then quickly pull the filament back.
    I hope you mean that your bowden tube was not against the heat break, rather than the nozzle. If it's against the nozzle, it's going too far into the assembly. It should stop well clear of the heater block and only part way into the heat break.

  8. #8
    Student 686 Shooter's Avatar
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    Yep, i meant the heat break. I'm not a smart man. Lol

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