DIY Lock Nuts

If you have a metal lathe just looking for some work, why not make your own lock nuts? That’s what [my mechanics insight] did when faced with a peculiar lock nut that needed replacing in a car. We can’t decide what we enjoyed more in the video you can watch below: the cross-section cut of a lock nut or the oddly calming videos of the new nut being turned on a lathe.

The mystery of the lock nut, though, isn’t how it works. The nylon insert is just a little too small for the bolt, and the bolt, being harder than nylon, taps a very close-fitting hole in the nylon as you tighten it. The real mystery is how that nylon got in there to start with.

As the video shows, you fabricate the nut with an open area to accept the nylon ring. Then, you use a tool to crimp the edges down to trap the ring. The video shows all the pieces being made: the nut, the ring, and the crimping tool.

As you might deduce, the crimping tool has to be harder than the nut material, so that takes some extra effort. But all the work is done on the lathe except the crimping. He uses a vise, but we’d imagine that an arbor press is more commonly used.

Lock washers and nuts seem like a simple topic, but it is way more complex than you probably thought. Way more complex.

Thanks to [the gambler] for the tip!

19 thoughts on “DIY Lock Nuts

  1. Nice work, but I wonder if you could just mill a depression inside the nut and then pour some compound into the head of the nut and then mill most of the hardened compound out to get the equivalent of a lock nut without the need of the crimping tool?

  2. As a boy in the ’70’s, I worked for a rancher. One day in the shop, he needed a lock-nut. He said, “come ‘ere; this is how you make a lock nut.” He took a nut and put it standing on edge on his anvil and gave it a couple sharp raps with his hammer. “Now, it’s a lock nut.” His technique worked like a champ.

    1. Yeah, the thread interference type of locknut (prevailing torque locknut) is well known in industry (they call the deflection at the top of the nut “coining”). The only issue is that it works by metal on metal interference which means firstly that you’d better not be running that sucker on and off more than two or three times (ideally one and done, really) and secondly the friction is pretty unpredictable so you don’t really know the torque margin (and therefore the clamping force of the joint). In the specification for the one I used, the acceptance test for drive torque onto the screw (prevailing torque) was to be performed lubricated. This presumably would reduce the prevailing torque level enough to ensure the torque margin in the joint was sufficient. In our case for production, lubricating the joint wasn’t feasible so there was really nothing to do but increase the torque specification. Naturally that isn’t really the best solution… but since I since I was never consulted again on this issue it was probably sufficient.

    1. He’s doing a extremely detailed restoration of a Datsun 240Z on his main channel, so this is mostly about making an accurate duplicate of a no longer available OEM part – it’s a weird size, so commercial replacements are unavailable. It’s probably the only reason to not just change the bolt to the nearest easily obtained size.

  3. If you watch many of the videos by this creator (all of which I highly recommend, very soothing) he has a highly functional arbor press that he’s restored. If he didn’t use it, I can’t help but think this requires too much force or something.

  4. The nylon lock nut allows the reuse of the bolt/screw. A regular nut with thread locking liquid will serve the same purpose and allow the reuse of the nut and bolt. Alternately there are metal nuts that have been deformed to work the same as the nylon lock nut. Then there is the technique to peen the nut at the thread interface. The double nut technique (already mentioned) often has ‘lock nuts’ available where the lock nut is half the height of a regular nut (also known as a jam nut). The jam nut also provides extra strength because of the extra threads used. But none of these are as much fun as making your own if you have the time.

    1. On small lathes, the forces associated with rollers and knurling tools can damage the lathe, unless they’re specially designed scissors-type devices. Making one of those is definitely more work than crimping.

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