Locking Up Lock Washers

We’ll admit most of us are more comfortable with solder and software than mechanical things. However, between robots, 3D printers, and various other mechanical devices, we sometimes have to dig into springs, belleville washers, and linear actuators. Unless you are a mechanical engineer, you might not realize there's a lot of nuances to something even as simple as a nut and bolt. How many threads do you need to engage? Do lock washers work? [Engineer Dog] has a post that answers these and many other questions.

The top ten list starts off with something controversial: split ring lock washers don't work. The original post cites a paper that claims they don't except in very special circumstances. However, he updated the post later to say that some people disagree with his cited study. In the end, you’ll have to decide, but given there are other options, maybe we’ll start using those more often.

Speaking of other lock washer options, have you ever seen a Nord-lock, a serrated flange nut, a castle nut, or a slotted nut? He also mentions chemical lockers and nylock nuts, which we have used before. How about a DTI smart bolt?

The post also repeats a rumor we’ve heard before that Phillips head bolts are made to cam out — that is, have the screwdriver jump out of the hole — on purpose to avoid overtightening in aluminum aircraft panels. A few cam outs and you have a stripped out head. It isn't clear it is really a design feature, though, as the original patent from John P. Thompson doesn't mention it. A later patent does seek to reduce the amount of "throw out", though, so it may have been an accidental feature.

We talked about lock wire in the past, which is yet another way to secure critical fasteners. We’ve also had a talk about Nord-lock and jam nuts. Want to hold your stuff together? You need to know this stuff.