Fail Of The Week — Accidental Demagnetization

There’s a trick in the world of plastic enclosures. The threaded insert is a small cylinder of metal with threads on the inside and a rough edge on the outside. To make a plastic part with a hole for securely connecting bolts that can be repeatedly screwed without destroying the plastic, you take the threaded insert and press it (usually with the help of a soldering iron to heat the insert)  into a hole that’s slightly smaller than the insert. The heat melts the plastic a little bit and allows for the insert to go inside. Then when it cools the insert is snugly inside the plastic, and you can attach circuit boards or other plastic parts using a bolt without stripping the screw or the insert. We’ve seen Hackaday’s [Joshua Vasquez] installing threaded inserts with an iron, as well as in a few other projects.

This trick is neat. And I’ve now proven that it does not work with neodymium magnets.

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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.

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