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Here is a picture of what I intend to use:

Enter image description here

I believe (and could be wrong about this) that over time as the structure is moved, the nut that was fastened to hold the structure together will gradually loosen. Is there way to make the nut so tight and fixed that it will never become loose automatically, but only when the user needs to open it?

Peter Mortensen
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quantum231
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    Clarify please; do you plan on the fastener being easily removed regularly with hand tools? Or is it acceptable to make it permanent and require destructive removal ? – Criggie Jan 22 '23 at 11:50
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    If we knew what the structure was, and was made of, we may well come up with better fixings than nuts/bolts. – Tim Jan 22 '23 at 15:34
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    Note, the OP's use case is here. Also, it's highly unlikely that anything more than a pair of washers and a good, firm snug on the wrenches is necessary to keep this particular assembly "tight enough". Unless you're moving the desk on a regular basis, that's all you're going to need. This won't just fall apart on its own - there are no inherent vibrations as there might be for bolts on a car. – FreeMan Jan 23 '23 at 16:22
  • OK, the bolt will keep together two panels of chipwood, where one is put on top of the other and bolted togeher. Then the panels are connect vertically in a desk so their face is facing wall. When can bolts loose overtime, I am not sure. – quantum231 Jan 23 '23 at 22:51
  • I hope Handy Mandy reads this thread... – Michael Jan 24 '23 at 20:39
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    @quantum231 I've noted several follow-up questions on several of the answers. While I fully understand that you're a beginner and you need to learn (learning is GOOD), you're seriously overthinking this! Have any of the bolts on the original desk come loose while the desk was just simply sitting there? If you're moving it all the time, then yeah, it could be a problem, but for 99.999% of us, a desk, once assembled, just sits there and desks. Bolts don't just come loose on their own on stationary objects. Moving objects like cars, dishwashers, etc. are a different story. – FreeMan Jan 25 '23 at 13:24
  • I wish I had a carpentar friend so I could ask everything. I am a senior electronic engineer and end up having to critically think about everything. Anyway, I am satisfied with the information I have. This topic is closed now. – quantum231 Jan 27 '23 at 16:35

15 Answers15

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The easiest way is to replace the nut with a Nylanut AKA Nyloc nut: enter image description here By Original uploader was Btarski at en.wikipedia. - Originally from en.wikipedia; description page is/was here., CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=5047606

These provide resistance such that it will not (easily) unscrew unless you use a wrench/socket to remove it.

You could also use a lock washer between the nut and the washer.

FreeMan
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DoxyLover
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    Or Threadlocker, or... Red threadlocker (not great for wooden things joined - the blowtorch needed to convince it to let go might scorch the wood a bit.. – Ecnerwal Jan 22 '23 at 01:04
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    Good answer, but use a tool kind of imply's a special tool, instead of a little bit more force with common wrenches/ratchets. – crip659 Jan 22 '23 at 01:13
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    @crip659 I agree and made an edit. – DoxyLover Jan 22 '23 at 01:43
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    Another option is to use locking nuts - have two nuts - tighten once as normal and then tighten the second while holding the first. This is the old way of doing it :-) – Rohit Gupta Jan 22 '23 at 03:40
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    Remember nylock nuts are supposed to be single use only. Subsequent reuse has a lower resistance so they come off easier. Enough reuse, and the grip degrades down to that of a plain nut. – Criggie Jan 22 '23 at 11:52
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    @Criggie even winding them down a long thread on assembly reduces the hold, at least on small sizes. – Chris H Jan 23 '23 at 10:51
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    @RohitGupta jam/lock nuts like this are still often the best solution for a solid hold without preventing future adjustment/disassembly. That's how a lot of bike bearings work, for example. You can buy thin "half nuts" to use as the locknut if space is limited. – Chris H Jan 23 '23 at 10:53
  • Based on the OP's use case, Nylocs will be sufficient, as would thread locker or a simple lock washer. – FreeMan Jan 23 '23 at 16:16
  • Rohit has given a very good and simple trick. For Nylocs, the basic idea is that it will exist at the end of the bolt and prevent it from loosing. The Nyloc will live at the end of the bolt such that the bolt might have some freedom to move horizontally in the hole that it lives in, but will never fully open and come off. Is that correct? – quantum231 Jan 23 '23 at 22:53
30

Thread Lock Adhesive

You can use a thread locking compound, such as this. enter image description here

user296800
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    Welcome to the site - good first answer. You might want to call out the different "strengths" of thread locker, like "hand tool" vs "heat release" – Criggie Jan 22 '23 at 18:31
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    Note that thread locker doesn't work on all metals. There are primers available that are basically copper oxide suspended in a solvent that remedy this. Thread locker also takes (generally) 24 hours to cure at room temperature. It's a good idea to spend 5 min reading the manufacturer's instructions before using it. – J'e Jan 23 '23 at 15:39
  • I'm confused! I always though blue Locktite could be loosened with tools, while the red required heat, yet this package seems to indicate that the red can be removed with "hand tools". – FreeMan Jan 23 '23 at 16:19
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    @FreeMan, welcome to the world of Loctite, where the (standard) blue threadlocker comes in a red bottle and the (high strength) red threadlocker comes in a blue bottle. {facepalm} – computercarguy Jan 23 '23 at 16:40
  • ummm... What. The. Heck??? (Funny story: I've got a bit of thread locker in my toolbox. It came with something I had to assemble and it's a blue liquid in a white bottle. May or may not be Loctite™ brand...) – FreeMan Jan 23 '23 at 16:49
  • My purple loctite came in a red bottle as well. Only the name (low strength) is in purple. I almost grabbed the wrong one the last time I used it and put high strength on a faucet's retainer bolt. – jeffatrackaid Jan 23 '23 at 22:42
  • I did not know something like this existed. I am truly fascinated by the answers. – quantum231 Jan 23 '23 at 22:55
25

You can also find bolts with a locking nylon patch applied, like these from Nylok: enter image description here

These are useful if the bolt is going into a blind threaded hole.

Added The Following

As I said in a comment below, these are considered superior to even locking adhesives in that chance of an assembler applying the wrong amount of locking compound is eliminated.

For our hi-rel applications, there's a specified process that's followed when using these, and similar fasteners, which include the following:

  1. The bolt is torqued to the proper setting, using a calibrated torque wrench. There are always two operators involved, one to do the tightening and another to witness that the proper torque was used.
  2. Depending on the application, we may apply a dab of structural adhesive to the head of the bolt to further ensure that it won't back out.
SteveSh
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    Wasn't aware of those; thanks for the tip! – keshlam Jan 22 '23 at 04:19
  • Nylok nuts have been around for a very long time - are these new in comparison? – Tim Jan 22 '23 at 10:59
  • @Tim - I don't know when those nylon patch fasteners first showed up. We've been using them for at least 20 years or longer in the aerospace industry. – SteveSh Jan 22 '23 at 13:22
  • Depends so much on the usage...for safety critical usage the nylon is probably better, but for normal home use the adhesive is way more practical. The adhesive is more flexible--you don't have to plan ahead, just use it with whatever you've already got. Especially helpful if you tend to modify or repair existing things that come with hardware. And the actual hardware is reusable, if you bolt everything together and then need to open it up again you're only out a tiny bit of adhesive. – user3067860 Jan 23 '23 at 16:01
  • Wait, this is a nylok bolt instead of nut? Who knew? This is awesome info, thanks! – FreeMan Jan 23 '23 at 16:18
  • @user3067860 - Agreed that for most home use & DIY applications, the adhesive is more practical. It is way, way cheaper and easier to obtain than the bolts-with-nylon-patches. – SteveSh Jan 23 '23 at 19:26
  • I never knew such a thing even existed. – quantum231 Jan 23 '23 at 22:54
  • I ran across this type of screw when I visited Costco because my eyeglasses screw was too loose and fell out. They replaced the screw with a screw which had "loctite" pre-applied to it, like the kind mentioned here. – jrw32982 Jan 27 '23 at 20:02
19

Lock Nut / Double Nutting

If there's enough thread exposed through the joint, then you can fit two nuts. The first nut is tightened to the required torque for your application, and the second nut is then tightened against the first nut, to a higher torque value.

Traditionally the locknut has been thinner than the main nut, but it is possible to just use two of the same nut.

Example - the locknut may have a larger diameter than the original nut, or it may be the same.
enter image description here

There is some debate about whether the thin locknut should be on first (as pictured) or the correct way where the main nut takes the load and the thinner lock nut goes on last.

Criggie
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    This site recommends the thin nut coming first, as in the picture https://www.boltscience.com/pages/twonuts.htm – Bobby J Jan 22 '23 at 16:57
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    @BobbyJ yeah there's three schools of thought, and valid points for all of them. And if one's better than another, its a very small difference. If your application depends on that difference, then the fastener is under-specced so upsize the biolts. – Criggie Jan 23 '23 at 02:31
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    Those are typically called "jam nuts" IME. – Huesmann Jan 23 '23 at 12:12
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    you mean a pinch nut! – Turbo Jan 23 '23 at 21:05
  • @turbo There's probably as many different names for this as there are for a pinch-bar. It's good to have them so search engines can find the words. – Criggie Jan 23 '23 at 21:21
  • I see, use two nuts that have different depth. Most interesting, – quantum231 Jan 23 '23 at 22:56
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    @quantum231 they don't need to be different thicknesses – Chris H Jan 24 '23 at 10:28
17

To round out the smorgasbord a bit:

Drill a hole through the nut and bolt when tight, insert a cotter pin.

Or drill a hole only through the bolt and use a castellated nut. Actually two holes at right angles allows finer adjustments (1/12 of a turn rather than 1/6th of a turn to line up one of the holes with the slots in the castle-nut)

Or use safety wire after drilling the hole. https://en.wikipedia.org/wiki/Safety_wire

Ecnerwal
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  • This works only when there's enough room to get a drill plus bit in close enough to get the hole something like parallel to the object/s being bolted together. – Tim Jan 22 '23 at 11:01
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    Safety wiring nuts used to be standard practice in the aerospace industry. For the most part, that has been replaced with the nylon (or some other substance) locking patch I showed. These are considered superior to even locking adhesives in that chance of applying the wrong amount of locking compound is eliminated. – SteveSh Jan 22 '23 at 13:03
  • When I worked one summer as a machinist's helper building heavy mechanical cranes for unloading container ships, we did this. Sometimes we would have the nut welded in place instead. It depended on the specs. – Wastrel Jan 22 '23 at 14:32
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    As it happens, today I was attending a criminal prosecution involving a split pin in a castellated nut on a heavy mechanical crane. Something about the pin not being correctly placed and the resulting accident.... – david Jan 23 '23 at 07:54
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instead of (or with) a regular washer:

enter image description here

you can use these tension ones:

enter image description here enter image description here

then there is also one with a rubber side:

enter image description here

as for a nut already suggested:

enter image description here

or two regular ones and lock the first one with the second:

enter image description here

or hardlock nuts:

enter image description here

of course the best (one time) securing is to weld bolt and nut:

enter image description here

servant0
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    This is the most comprehensive answer but everyone has provided valuable input. I hope page will help people in the future. – quantum231 Jan 24 '23 at 21:22
9

Flange washer

This solution requires modification to the bolt, in the form of a channel or slot running up one side.

Then a washer with a tab/flat is slid on before the nut, something like this:

enter image description here

Once assembled and torqued down, the washer is deformed around at least one side of the nut, by using leverage often from a large flathead screwdriver/crowbar and hammer.

This mechanism is common on car wheel bearings. Here's a photo from an old landrover. In this example, the washer is sandwiched between two nuts and one segment of the washer has been folded back (away from camera) and another sector is about to be folded forward around the visible front nut.

enter image description here

Criggie
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    Had never heard of this method - very interesting, thanks. – Armand Jan 22 '23 at 16:02
  • @Armand yeah its more for older cars Mine's a 1973 and the tech was old then. The washer has to be unfolded to get clearance to undo the nuts, and you could get 2, maybe 3 uses before you're re-rebending metal. Like nylock nuts, they have a usage cycle or duty count before needing replacement. – Criggie Jan 22 '23 at 18:27
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    Land Rover Defender? – Lamar Latrell Jan 22 '23 at 19:20
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    Wheel bearings I've worked with had a hole in the spindle and a special nut that was used along with a cotter pin to prevent the bolts from backing out, after it had been torqued down correctly to pre-load the bearings. – SteveSh Jan 23 '23 at 15:11
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    Yup, this is a technique used on more than a few axle nuts, even on newer cars. My VW has a different technique, though: 105 ft/lbs then turn an additional 180°. Stretches the bolt, locks the threads, makes the bolt a 1-time use. – FreeMan Jan 23 '23 at 16:22
  • What exactly can cause bolt to become loose overtime, isn't using something like lockwasher mentioned in answer from QTX enough? – quantum231 Jan 23 '23 at 22:58
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    @quantum231 vibrations (that's the main culprit of bolt loosening) as a byproduct of high RPM. because even "balanced" wheels from a car are just balanced to be "good enough" and not "totally perfect". and even if they would be, then even the smallest rock/pebble can unbalance them and introduce a shockwave of vibrations – servant0 Jan 24 '23 at 21:35
  • @quantum231 Heat-cycling comes into it too. Bearings can get hot, and it can be a nasty dirty wet environment. Plus the forces on a wheel can be enormous, able to override the resistance of a simple system. – Criggie Jan 24 '23 at 23:17
9

Lockwashers like these can be useful in some applications.lockwashers

QTX
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  • These would be "crinkle washers" to me - other areas will likely have different names. – Criggie Jan 22 '23 at 18:28
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    You might choose to include split washers and nordlock washers here too, as a retention system under the nut. – Criggie Jan 22 '23 at 18:30
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    @Criggie - they are star / lock washers to me. Crinkle washers are different, they are literally a very thin flat washer that is crinkled to provide some force when a nut is fastened down on-top, rather than cutting into the surface, like the ones pictured. – SiHa Jan 23 '23 at 08:36
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    IME, these don't really work, and people tend to over tighten them so they break/fail. – computercarguy Jan 23 '23 at 16:43
  • Does such washers exist for bolts or just small screws? I have seen these type of washers when I was passing by in shop once upon a time, I did wonder what they could be used for. – quantum231 Jan 23 '23 at 22:57
  • @quantum I have a box of assorted star washers, something like M3-M10 (1/8"--3/8"). They're not great, but might be of some help here – Chris H Jan 24 '23 at 10:29
7

Torque the bolt properly.

This preloads the bolt up to some percentage of the breaking load. Under normal use the clamping preload should be greater than the dynamic load the bolt sees.

As a consequence of the clamping force being larger than the preload, it will not deform elastically during use, and then nut will not work loose under most conditions.

vidarlo
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  • Bang on. I'll just add that if the torque setting isn't known for the assembly, then hand-tighten and then use a (torque-)wrench to turn the nut tighter through 90 degrees. This suppresses fatigue-inducing dynamic loads. – Trunk Jan 23 '23 at 12:05
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    Or you can look up standard values for the bolt you're using. For instance a M8 10.9 zinc plated? 29 Nm. This is a good enough value if nothing is specified. – vidarlo Jan 23 '23 at 12:22
  • yes, certainly this is the most useful answer, i.e pre-empt the loosening of the bolt. – quantum231 Jan 23 '23 at 23:00
  • @vidarlo the OP is bolting together veneered chipboard. You'd need big washers to spread the load and avoid crushing the veneer – Chris H Jan 24 '23 at 11:17
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    @ChrisH That's not mentioned in the question. A comment by someone else claims this. As the question stands this (and other answers) are perfectly valid. – vidarlo Jan 24 '23 at 11:52
6

Another, way more permanent plan is to have the bolt about one thread's worth protruding out of the nut. It may well involve cutting said bolt. Then peen the extra thread over, and the two will never work apart.

If the structure needs to be moved frequently then perhaps a different fixing would do a better job. Pop rivets, welding, for example.

Tim
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4

Lockwasher, locking nut as shown above, threadlocker blue (the removable kind) (choose all three)

BrianK
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    This does not provide an answer to the question. To critique or request clarification from an author, leave a comment below their post. - From Review – gnicko Jan 22 '23 at 04:11
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    @gnicko Suggesting 3 ways to solve the issue seems like an answer to me; could you clarify? – Armand Jan 22 '23 at 04:46
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    @Armand probably cos its short and lacking in detail, and was posted after a couple of other longer answers covering similar points. – Criggie Jan 22 '23 at 12:16
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    This seems to be the only answer mentioning liquid threadlocker, which in my limited experience is by far the most common locking technique used in auto repair. – Armand Jan 22 '23 at 16:08
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    This has the beginnings of a good answer with the threadlock suggestion, but as written it's just a series of brief comments on other answers that came before it. – gnicko Jan 22 '23 at 19:45
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    @gnicko: Agreed it's not a very good answer, especially not mentioning what "threadlocker blue" is. But it is an answer. And it was better than nothing before other answers with more detail were posted, since "threadlocker blue" and the others are searchable terms. It's low enough quality that it didn't deter people from mentioning the same things in their own answers. Unless this stack is very strict about not answering in comments, though, this is the kind of thing that I'd have posted as a comment. But posted as an answer, I'd say it is an answer, just not worth an upvote. – Peter Cordes Jan 23 '23 at 05:30
4

Depending on the application, you can tack weld the nut to the bolt. Of course this weakens the nut and bolt, and you'll need a torch or grinder if you ever want to remove it, but I have seen this technique successfully used many a time.

Joel Keene
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    I've seen this used to secure remote farm gates, to keep trespassing 4WD drivers out of private land and prevent them lifting a gate off the hinges. A small portable and self-container welder is invaluable on the farm. – Criggie Jan 23 '23 at 02:35
4

Aircraft used safety wire through the nut/bolt for critical applications. ( May have changed in the many years since I saw them.)

blacksmith37
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    Probably too hardcore – DKNguyen Jan 23 '23 at 02:14
  • Goodness yes, I remember doing this as an apprentice. – RedSonja Jan 23 '23 at 07:24
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    Not only aircraft. It's used in industry in general where positive locking is required. It also makes inspection very easy, which has a benefit in some industries. If wire is undamaged, bolt is OK. – vidarlo Jan 23 '23 at 08:54
  • But you have to check that the wire is running the right way - to tighten, not to loosen. Don't ask how I know that. – RedSonja Jan 23 '23 at 11:45
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    Also safety wire requires a fixed point to tie the other end to, often another bolt if there's one close enough. These are definitely still in use in modern industrial/military installations, but the place they're installed generally has to be designed to use them. – Darrel Hoffman Jan 23 '23 at 19:22
2

The most important thing to do is to ensure that, in the final assembly, there is no rotational degree of freedom around the axis of the bolt.

For example, I have a number of cooking pans where a single bolt holds the handle to the pan. They all repeatedly come loose and require re-tightening, because the handle can rotate slightly back and forth around the axis of the bolt. But the same can happen in arrays of multiple bolts, e.g. corners of a rectangle where sides are independent pieces, where the positions of the bolts aren't held rigidly relative to one another, allowing them all to rotate back and forth. No matter what you've done to try to prevent loosening, bolts that act as pivot points will always loosen.

To solve this, you need to have enough bolts, in the right places, to rigidly constrain the whole assembly against this. At that point, you can think about other measures to eliminate loosening from vibrations and other smaller-order effects.

Toby Speight
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R.. GitHub STOP HELPING ICE
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    Pans are also subject to heat-cycling which will back out threaded fasteners over time no matter what. The best fix is having the cooking base and handle cast from the same metal at the same time then adding a heat-resistant covering to the handle. – Criggie Jan 24 '23 at 23:22
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    @Criggie: I'm skeptical of that claim, in the absence of rotational motion. I don't experience that with properly torqued threads in 3D printer hotend. But even if it does happen, that's one of the smaller-order effects I was talking about mitigating with other measures. The dominant problem is the rotational degree of freedom. – R.. GitHub STOP HELPING ICE Jan 25 '23 at 05:17
1

Linseed Oil

If you are working on odd-jobs and have an average garage at your disposal, linseed oil congeals to a rubber consistency (See info about polymerization of linseed oil) .

enter image description here

bandybabboon
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    This is the old-school way of thread locking. Bicycle wheels use "spoke prep" which was originally linseed oil on initial assembly, allowing smooth tightening of spoke nipples while truing the wheel, which cured after some time and resisted future drift/movement without completely eliminating it. – Criggie Jan 24 '23 at 23:19