Active Strain Relief For 3D-Printer Filament

Buying 3D-printer filament is little like eating potato chips: you can’t stop at just one. You start with basic black PLA, then you need a particular color for a special project, then you start experimenting with different plastics, and before you know it, you’ve got dozens of reels lined up. Trouble is, unless you move the in-use reel right over the printer, the filament can get a bit unruly as the printer sucks it up. What to do?

How about building an active strain relief system for your filament collection? That what [Daniel Harari] chose to do, and we have to say that it looks pretty slick. The idea is to keep the filament slack before it enters the printer’s extruder no matter where the reel is positioned relative to the printer. The active bit is a little like a low-force extruder, using a couple of pinch rollers from an old 2D-printer to pay out filament when needed. A clever sensor, consisting of a 3D-printed funnel and a copper wire contact loop, detects when the printer has taken up all the slack in the filament and triggers a payout from the feeder. In a nice touch, the feeder motor is controlled by a couple of 555s rather than a microcontroller. The short clip below shows the feeder being triggered and paying out a little more slack.

In the final analysis, this is just another in a long series of filament management projects, from dry-boxes to filament meters to end-of-spool alarms. It may be overkill, but [Daniel] put a lot of thought into it, which we always appreciate.

26 thoughts on “Active Strain Relief For 3D-Printer Filament

  1. I mostly use black and white, sometimes semi-transparent PLA and that’s it… even though I print regularly. Couldn’t imagine so many spools accumulating (not to mention they don’t get any better once unwrapped). Guess I’m just a bland, boring person who hates colors.

    1. 3d printerers seem to hate paints and I don’t really know why. If colour is important for your project, how come painting that’s been used in every kind of design since forever is suddenly not an option? Maybe 3d-printing plastics are hard to paint?

      1. Lots of people paint stuff off their printers. I don’t but I’ve printed for other people who’ve painted it.
        My reason, everything I seem to print is a functional printer part, where colour isn’t that important

        1. There are lots of people that care about how their printer parts look too. For many a printer is their biggest project, it has to represent their skill with it’s looks. But why would they want to paint it? Especially parts that need to fit together and/or move against one another. Would they leave a little extra slop in all their designs to account for the thickness of the paint? And worry about scratches?

          It’s better just to start with already-colored materials.

      2. Paint scratches. If you scratch your colored plastic you only uncover more colored plastic. If you scratch your paint the color beneath makes the scratch really stand out. That’s my number one reason. Colored filament is so much better than paint!

        Need more reasons not to chose paint?

        It’s messy.

        It’s an extra step.

        It adds an element of human error. Whoops, got it too thick! drip drip drip

        It adds an element of non-human error. Ever paint outside? Ever have a little gnat land in your otherwise perfect coat of paint that you were proud of a moment ago? Dust? Whatever else travels through the air?

        For those outdoor only types of paint don’t you just love waiting for the perfect weather? Or not waiting, trying to push it and getting an ugly result?

        Is that enough reasons?

        Also, why not use colored filament? Don’t want to buy the multiple rolls? Well, when your one roll runs out you are probably going to buy more anyway aren’t you? Just store it well. I store mine in sealed plastic containers that are meant for holding baked goods. I put packets of silica gell in there with it. Then since I don’t know if my semi-transparent containers block UV or not I keep those boxes stored away from light in a wooden box that closes.

      3. Tom wrote up a nice piece on painting 3D prints. Spoiler: lots of sanding, and primer.

        Donald Papp experimented with UV resin and smoothing, to cheat on the sanding:

        But we’ve seen a ton of projects where folks take the extra step.
        or even the functional (just last week?)

        In short, painted 3D prints are all around. But it’s hard work, so you have to really care.

    2. There are other reasons than color to change filament, like using POM/Delrin for small gears, TPU for flexible parts, ABS for UV/heat resistance, nylon for mechanical resistance, PETG as a compromise between PLA and ABS or wood filament for wood-like objects.

    3. No man, youre NOT blan and boring, if you need something 3D Printed and/or designed, its totally up to you if you want it a specific colour or not. Dont give a damn what others think, THEY are not the ones going to be using your 3D Print, YOU ARE !!!

      Even if the public are going to use your design because youve put it up on a sharing website or emailed it, then again its up to that individual’s personal preference whether or not to use a coloured filament or prepare the 3D Print for pain.

      Does at all make you boring and anyone that thinks so needs a good old fashioned shlap and a kick in the teeth lol

    1. Exactly my thought. The amount of pull needed to get the funnel to move looks a bit too much as well. I just printed an adjustable-width stand and used sealed bearings on it for friction. Works perfectly.

    1. One of the first things I ever printed was a filament “colorizer”. It’s a thing with a small hole in the middle that you run your filament through just in front of the extruder. It has larger holes on the sides that you jam felt markers into. Rubber bands hold those in place.

      The idea of course was to stock up on a bunch of non-colored filament and print all sorts of colored items just using markers.

      Unfortunately I found that it added enough resistance to the filament path to cause under extrusion problems. I set my colorizer aside and meant to come back to it at a later date after building something like this to pull the filament off the roll. That way the colorizer would be the only resistance the extruder woudl have to counter and maybe that would be enough help to make it work.

      i never got around to it but shorter version: not absolutely unnecessary for me!

  2. A year or two ago I saw something like this on Thingiverse. I meant to come back and build it, didn’t get to it in time and now I can’t find it again. Anyway, that one was much simpler.

    The one I saw then ran the filament across a little bar that held it up when it was slack. When the extruder pulls the slack the bar would move and trigger a microswitch. The microswitch controlled a plain old DC motor which turned some form of pinch wheel pulling filament off the roll until there is slack again.

    The only circuitry involved was the microswitch and a power lead coming from the printer’s power supply. I suppose if one were concerned with the lifespan of the microswitch running 5 or 3.3 volts through it and using that to switch a MOSFET might be a better design.

  3. I’ve been 3D-printing pretty much all the time since 2015 and my immediate reaction to this is: I would never add another moving part to my printer unles it had an absolutely vital function (and this is not vital, IMO).
    Things break. Many things together break often.

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