More on tightening threads

This is a deep, serious discussion of mechanical esoterica, with implications to life in general, so if you’re not interested in mechanics or in life lessons, go back to doing your nails, watching TV or stressing over your made-up relationship drama.

If you get the clamp screws tight enough, you probably don’t need the Locktite. If you don’t get the screws tight enough, the Locktite won’t help.

Thank you for sticking it out all the way to the end of this post, though if you needed to read it, you probably didn’t, and if you didn’t need to read it, you most likely did. I’m preaching to the choir then. Still it must be said.

25 thoughts on “More on tightening threads

  1. Amen, brother! Preach it! BTW, for those who don’t already know, Loctite tastes TERRIBLE. Trust me on this. No need to verify my finding for yourself.

    • Precisely. You know it.

      And that is why we supply an extra screw. In our destructive testing, it is the screw, and not the more expensive and exclusive clamp, that breaks.

      For them what has experience however, they know, by intuition, the feel and temperament of a screw, nut or bolt that’s as tight as it “wants” to be, just *before* it starts to yield. This is because any given material has some stretch to it, and when that stretch is taken up, it begins to yield. The perceptive individual senses this and avoids getting into yield territory, even if he can’t put it into words. For an excellent and detailed explanation of this phenomenon of “empathy” with the material, see the book Zen and the Art of Motorcycle Maintenance.

      I forget what the book is about exactly, but I remember well the treatise on thread tightening, as it is brilliant. The best minds in political and hostage negotiations, marital counseling or haggling, could learn from it.

      • I deal with similar concepts in my work in QA. One of the things I’ve had to handle of late is explaining to people why we have torque ratings on things.

        Yes, you can torque a nut onto a bolt a little higher than the rating. We don’t recommend it. Why? Because that’s outside the recommended tolerances and we can’t guarantee there won’t be a failure.

        And yet we get customer complaints of ‘your part failed’ when it’s insultingly apparent that they put two hundred foot-pounds of torque on a U-bolt rated to 45 and probably not capable of handling much beyond 70.

  2. This post is a little esoteric. I’m not completely clear on the “tight enough” part? For those of us not immersed in the manufacturing or repair business…..

    • G-dammit. I hate when I f-ck up the joke. That should read, “CAN YOU ELABORATE on the ‘tight enough part.'”

      Nevermind. I screwed it up and now it’s just a great big steaming pile of fail. I’m gonna go smash my fingers with a hammer.

          • I see no indication of such an overlap. She claims she lives in California near Los Angles and that is where her IP address resolves to.

            And, except at the occasional times where she comes across as a troll, her contributions are welcome here.

            That doesn’t mean one couldn’t easily make a joke somewhat at her expense. I would do so but I think she already receives more hostility here than she actually deserves.

  3. The safety lever on my Lee Enfield Mark III rifle has a stripped bolt hole. The safety actuator stays on the gun unless and until operation of the safety, or firing the rifle, at which point the screw loosens and/or falls out. I don’t fire this 1917 rifle any more, ever since I found the screw & lever on the floor at the range the first time it happened. Thankfully, I have the bayonet in case of sudden Huns.

    Locktite won’t fix anything safely; the threads in the receiver metal are too far gone. I could perhaps ream the hole a new threading, and obtain a larger screw to hold the safety, but it would require drilling a larger hole in the safety lever, too, and hey, I have other guns I shoot more and don’t want to spend money on a reamer I’ll use exactly once.

    I will fix it right one day, though. And when I do, I will tighten the new screw just exactly so, per instructions in this post.

    • The most common repair to a stripped thread would be to install a threaded insert, to retain the use of an original screw. A possible complication to this is that guns in general tend toward uncommon thread sizes, and this is further muddled in that it is a British design, and may use one of the peculiar ‘British only’ thread formats. I suggest that you research this specific part very carefully, as it would not surprise me to find that the same gun could be made with different threads, depending on when and where it was made.

      When I serviced the British built Norton motorcycles in the early 70’s, I had three sets of wrenches and tap/die sets required. Whitworth, SAE, and Metric. Prior to ww2, there were multiple British thread systems in use. For some reason, they wouldn’t standardize a national system. Eventually, they moved to the Metric system.

      • A non-mechanically inclined buddy asked me to help him work on his old land rover he had inherited when I was in college. Much cursing was the result till I realized every bolt and nut on the thing was Whitworth. Up to that point I’d never seen anything but SAE and Metric.

        Given the age, British Standard Fine would be the first place I’d look to determine the threading, followed by Whitworth and then Unified. Whichever one it is, somebody somewhere probably makes a helicoil for it…

      • Sometime in the late ’60s when I too was wrenching motorcycles, I started a survey to see how many thread standards I could find on a 1968 BSA Lightning. I think I got to eleven. Not thread sizes, thread standards. Did you know that there WAS a “Cycle Engineers Institute”? Much less that they had a thread standard of their own?

  4. I’m a fan of thread locker when used properly in applications where vibrations and thermal expansion/retraction make “tight enough” a variable between “sheered off” and “fell out.”

    When used improperly, it’s generally worse than no thread locker at all.

    For those who are wondering when “tight enough” is, try degreasing everything. “Tight enough” will happen well before you think it would if there is any lube involved.

  5. Perhaps another esoteric subject worthy of attention would be the matter of magazine springs and “taking a set”. I am no metallurgist, but I understand from reading that properly heat-treated springs will not take a set over time, that only improperly heat-treated springs do so, but the only way to tell if the heat treatment was done correctly is to store magazines with loads on the springs for a time.

    • I dunno; I have a Victrola from around the 1920s with a clock spring to power the turntable. It gets “deep cycled” a lot, in between long periods of stasis at tension, and it’s still as good as ever.

      Rumors take on lives of their own, like “memory” in NiCad batteries. Your battery starts to go bad, and so that is proof of “memory”. In fact it was such a rare occurrence that aerospace engineers (satellites ran on NiCad batteries back then, see, the birds were terribly expensive to put up, and often their effective service life was limited by the life of the batteries, so they REALLY wanted to understand “memory” phenomena) had a very difficult time causing “memory” to happen in order to study it. Nevertheless, millions of terrestrial consumers bought those stupid battery dischargers, putting further cycling stress on and shortening the life of their batteries in order to prevent something that was practically non-existent. Very few ever thought tonlook at over-charging, which was and remains a battery life-shortening problem. But enough people talked about “memory” that it had to be a real problem, right? I mean; they wouldn’t sell those dischargers if they served no legitimate purpose, right?

      • The NiCad “memory” phenomenon was pretty well documented. I certainly experienced it with a set of walkie-talkies that sat in their charger-stands when not in use. I was clued in by a policeman buddy who knew about it because all of theirs had the same problem, and the radio manufacturer had explained it. The cause was crystal growth in the electrolyte.

        • Just because someone has an explanation for a phenomena, doesn’t make it true, even the manufacturer. When I took psychology in college, they had an explanation for how subliminal messages affected people’s behavior, but it turns out the whole thing is faked “science”.

          I had a brother of a friend tell me once in all seriousness that he knew that past lives were true because he could read people’s auras. How do you respond to that kind of thinking?

  6. Reminds me of the time I accidentally discovered a new type of explosive. I mistakenly put both anti-seize and Locktight on the same bolt, and,”BLAM!”

    Be careful out there!

    Shamelessly stolen from Doc at The Whiteboard comic. Read it. Seriously!

Comments are closed.