Worried About Running Out Of Filament Mid-Print? Join It!

If you’ve ever cringed over throwing away any printer filament you know wouldn’t cover your next small part — let alone an overnight print — you may appreciate [starlino]’s method for joining two spools of filament together.

While there are other methods to track how much filament you’re using, this method removes some of the guesswork. First, snip the ends of the filament on a diagonal — as close to the same angle as possible. Cover both ends with shrink wrap tubing — 2mm tubing for 1.75mm filament for example — ensuring that the two ends overlap inside the wrap. Tape the filament to a heat resistant mat with Kapton tape, leaving exposed the joint between the two filaments. A temperature sensor may help you to find your filament’s melting point, or you can experiment as necessary to get a feel for it.

Melt the filament inside the tubing with a hot air soldering station or heat gun and cool it down promptly with a few blasts from an air duster. All that’s left is to cut the filament free of the tape and shrink wrap, scraping away any excess so as to prevent printer jams. Done! Now, back to printing! Check out the tutorial video after the break.nning

21 thoughts on “Worried About Running Out Of Filament Mid-Print? Join It!

  1. Sounds easier than what I do, slowing the print and pushing the head of the new spool through as the previous one comes to an end. OTOH being hands on and in the printer’s face has always worked for me, being pretty paranoid I always move a laptop out to get something else done and am thus present to see or hear and stop anything with the print going weird or at least being there to cancel and restart the job.

    1. That’s the only way I’ve been able to do it successfully. When I’ve attempted to join two ends, they either fell apart, or had a thick blob at the joint which jammed the feed.

  2. You might want to look at the devices used to join Polycord belts.

    Doing a butt weld is faster and easier, and you can shave the bead off with a second device constructed like a pencil sharpener that opens up in the middle.

    1. Ah… now this is a method that I can see being worthwhile for saving filament leftovers. Especially so if you save up lots of filament ends to do at once so you are heating the tool only once.

    2. I know there’s also almost fully automatic machines that can make a perfect weld/connection of individual fiber optic strands.

      So the tech exists, it’s more a matter of simplifying, scaling and reducing price of it.

    3. Beat me to it! First thing I thought of, too, to heat both sides on a hot knife then butt join and trim the excess. Model engineers have been using this technique joining belts for small machine tools for many years.

  3. This looks like a cool way to create a color changing filament. That’s makes it a good technique to know but I think that’s about all it is good for.

    “If you’ve ever cringed over throwing away any printer filament you know wouldn’t cover your next small part ”

    You seem to be implying that one would use this technique to save money or at least to conserve supplies. I don’t see it working that way. Take the value of that small piece of filament scrap. Now compare it to the cost of the piece of heat shrink tubing, capton tape and duster spray. Note all the liquid from the spray.. he seems to be holding the can upside down. That technique gets you a lot more cooling at the cost of using up the can really fast too.

    Unless you only print really really big things, meaning your definition of ‘too small to use’ is really long then I’m pretty sure that cost-wise it is better to just toss the scrap filament. And this is me saying this, I hate tossing usable stuff. I prefer to save things both for monetary and environmental cost. But… I think this method of saving fails on both of those.

    That being said the video author doesn’t specify why one wants to join the filament. Maybe it’s for color changing purposes. There is nothing wrong with that idea.

      1. That is a pretty cool idea. I’m not sure I totally trust it, I am thinking that any variance in how much filament is used would throw it out of sync. Pretty cool though and I would love to play with it and see for myself if getting out of sync really is a problem or not. Using this on the side seems much easier than adding more extruders and hotends!

  4. It would be interesting to make this into a tool (similar to Dax’s video above, but with fewer steps). I’m thinking it would look kind of like a split ferrite core, with two halves of some heat-insulating material forming a tight-fitting cylindrical channel around the filament ends. In the middle would be an element to heat the join to the appropriate temperature. You’d just close the thing around the filaments, hit the button, wait ten seconds, then open it back up.

      1. Hmm, this reminds me of something… *takes a good look at wife’s hair straightener/flat iron*
        Seriously, most hair straighteners today have crude temperature control (good enough for this process), so all you need is to fabricate the holding metal bracket (quite easy). Hair straighteners are cheap (my wife’s hair straightener cost 10€/11.8$ new), used ones are even cheaper (flea market).

  5. lol – I can just see in my minds eye someone panicking as they try to use this technique as one side of 1 meter of filament is slowly going into the hot end of the printer….

  6. I like it! But….I can’t see myself doing this – Filament is so cheap, I’ll gladly just toss a roll with a few dozen feet left on it. The amount I would save would be pennies, and I stopped picking those up off the ground years ago.

  7. I just don’t understand why the printer can’t pause the print, purge the nozzle and ask for more filament?

    Filament swap should be a printer feature, where the only thing you have to do is give it the end of the new spool into a holder, and once it detects the old filament running out it runs the print head under the changing station and jabs the end of the filament into the feeder.

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