Custom Threaded Inserts For 3D Printing

There’s a variety of ways to add threaded holes to 3D printed objects. You can tap a hole, but the plastic isn’t always strong enough. Nut traps work, but aren’t very attractive and can be difficult to get exactly the right size. If you try to enclose them, you have to add a manual step to your printing process, too. You can buy threaded inserts (see video below) but that means some other piece of hardware to have to stock in your shop.

[PeterM13] had a different idea: Cut a piece of threaded stock, put nuts on the end and heat it up to let the nuts reform the plastic. This way the nut traps wind up the perfect size by definition. He used two nuts aligned and secured with thread locker. Then he used a hot air gun to only heat the metal (so as to reduce the chance of deforming the actual part). Once it was hot (about 15 seconds) he pulled the nuts into the open hole, where it melted the plastic which grips the nuts once cooled again.

Once in place, you could remove the threaded stock or use it as part of the assembly. Once you remove the displaced plastic, the result is a good-looking nut trap. If your metal/plastic fusion dreams run more to the electronic, you might consider printing these.

29 thoughts on “Custom Threaded Inserts For 3D Printing

    1. For a long time I had used coupling nuts and all thread epoxied onto caps for my Z axis rods to make a brace/hanger between the two rods. The caps had filament guides in them.

  1. Threading / tapping PLA usually works well for me. Or gluing in the nuts with 302 2K 5 min. glue. Works great with PLA and ABS.
    But this gives you nice, reliable threads – if you need to use the thread more than 10 times it is a good way to go.
    To optimize it I would maybe use an aluminum or copper screw and heat that to have better control of the alignment of the screw.
    If you really need to fasten something very tight, an additional hex nut does the trick – it spreads the pressure and before the thread fails the part fails.

    1. I have those cool taps from Harbor Freight that are at the shank end of the right size drill bit. So you put the thing in your drill, bzzzzz, and you come out with a tapped hole. With ABS and PLA you don’t even really need cutting oil. I’ve had good luck with this too, but the strength is not always good enough.

          1. Woops, my bad. They make an SAE set too. I think I still like a regular tap anyway. You can buy them in bulk packs of the usual sizes and throw them out after a few runs. Old taps will bite you, even with cutting fluid or wax.

      1. But that makes little sense for 3D printed objects, because you already printed your core-hole.
        So tapping alone is sufficient if you use the correct core-Ø from wikipedia.
        Tapping a solid part is not really a good option because you might have loose filling in there, while core-holes always get the print’s wall-thicknes and that is usually sufficient for tapping.

        PRO-TIP for those users planning or buying tapping-gear:
        There are two kinds of tappers: single-pass and 3-pass. For aluminum and plastics single-pass is great. For steel you might want to consider 3-pass :-)

        Then there are two sub-categories: For through-holes and pocket-holes.
        #1 has a gradually widening tap-cutter, so that you start with an unfinished thread and while driving the drill in it widens the thread. This means it is a little forgiving when starting the thread, but also that you have to screw it through all the way and even more to finish your tapping.
        #2 Starts with the end-diameter at the very tip so you are able to get a thread right to the bottom of your pocket-hole. This kind is harder to use since you have to make sure to get the right angle for the thread from the start.

        1. Yes if I’m using those I do not put a hole in and I’m printing fairly solid, or I put a small hole in place. Like I said, not always strong enough but it just depends on what you are doing.

  2. The downside to doing this is that unless you print a very dense part you will have very little material holding the nut in place. With a nut trap the slicer will add additional material underneath, above and on the sides of the nut, strengthening the location it is in.

  3. I’m glad somebody shared this, I’ve used a variation on this for situations where thread strength is not critical but wiggle room would be problematic. I have the slicer do an extra perimeter layer and design a plain hole into the part, then once it is printed I heat a machine screw up with a hot air gun and simply screw it in place and then back it out a quarter turn every 5 seconds or so as it cools.
    Using this trick I have been able to screw things to the part and have them stay firmly anchored. It works great with PLA but I have not tried it with other plastics.

  4. Note, instead of using a heat gun, with PLA, you can put the metal bits in boiling water. 100C will be enough to get PLA soft, but not liquid, and thus perfect for inserting tightly fitting stuff.

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