• Jam nut is (might be?) the cheapest/easiest/most reliable option I.e., 2 nuts stacked and tightened - standard nut and a jam nut. Or just 2 standard nuts would work I suppose.
• You can spec to foul/peen threads but that won't necessarily prevent the nut from "loosening" per se - but it will prevent them from coming all the way off the bolt. I use this for lightly loaded thru bolts.
• Red loctite. I've never spec'd it but some folks on here do.
• Pretensioning / SC. Never spec'd it for this particular reason. I'd hope they wouldnt loosen since we use them in slip crit framing connections, but those arent typically subject to constant vibrations.
• Nord-loc washers like you show above would also work.

Is this for a machine-to-structure connection? Or a standard framing connection (beam-girder, etc.) that is below a machine. Machine to structure connections are sometimes pretensioned by default.

Nord-lock (wedge) washers are pretty good. So much so that it's sometimes really difficult to undo the connection when you want to.
They work great in machines. I'm not a structural engineer so I don't how how suitable they are for structures.
They're an order of magnitude more expensive than plain washers though, so it's easy to overdo it and drive the cost of the machine through the roof if you're not careful.

Note that Nordlocks are not recommended for multiple disassembly cycles, since the wedges will get worn down, which will degrade its performance

TTFN (ta ta for now)
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first post (double nutting) is a good simple solution. A cotter pin will prevent the joint coming apart, though it will loosen.

another day in paradise, or is paradise one day closer ?

Thanks all

dold

It is standard framing connection beam to column. I will go for jam nuts and nord-lock washers.

Some alternatives ; jam nut, Loctite Red , peening or the use of spherically seated washers with hardened nuts
..


I would prefer jam nuts or the use of ​spherically seated washers with hardened nuts

why is a typical? "standard framing connection beam to column" subject to unusual vibration that standard engineering doesn't work ?

another day in paradise, or is paradise one day closer ?

Jam nuts won't do anything that pretensioning won't do in a standard steel connection. They both work on the same principal, adding pretension to the bolt to increase the frictional resistance between the threads of the nut and the bolt which prevents loosening. Jam nuts simply change the area that is preloaded to between the nuts, rather than in the entire grip of the bolt. They are useful for connections where material in the grip of the bolt is compressible and the required pretension can't be maintained. Examples of this would be through-bolting of HSS or cast in anchors where concrete creep causes the relaxation of anchor pretension over time.

For a standard steel connection a jam nut won't be detrimental but you will often find that A325 bolts do not have a long enough thread length to accommodate them (increasing the length of the bolt will often cause the first nut to bottom out on the shoulder of the bolt before properly clamping the connection), they will just be an added cost that does nothing to improve the performance of the joint and cause questions and issues come erection time.

The RCSC/AISC specifically requires pretensioning bolts in joints that are "subject to significant load reversal" (i.e. vibration) for just this reason - to prevent loosening.

Hi struggle67

I would use Nordlock washers they are very good however they are expensive and so it sdepends very much how many joints you have this problem with.
Do you have any information about the actual joint subjected to the vibration? You can preload the bolts to withstand the variation of load but without knowledge of the vibration what would you tighten them too.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

Anco locknuts

Quote (2 nuts stacked and tightened - standard nut and a jam nut.)

Is a bad choice and the thinner nut is on the bottom, if used. I often use Loctite 263 (Red) and have for decades... great stuff.

https://www.boltscience.com/pages/twonuts.htm

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

Mercedes Benz uses NORDLOCK on new military vehicles as well as many civilian applications.

If there is one place where a fine, exacting German reputation is on the line, its ensuring reliability of its military machines.

I disagree with the statements above that "you can drive the costs through the roof" by specifying NORDLOCK devices ... What is the cost when the joint comes apart ?

According to the vendor, NORDLOCKS can be repeatedly assembled and broken down... I believe them ... They have test data you can request

I have specified RED LOCKTITE over the years and it seems to be favored by anyone with an automotive background.

Two methods not specified above are:

1) Tack/spot Welded threads (a good method when a visual QA/QC is required on plain carbon steel nuts and bolts)... cannot be disassembled

2) Drilled and wired nuts/bolts (favored for decades by NASA and aerospace engineers) obvious, positive and cannot be disassembled.

There is no one "best" method for everyone.... the only best method is the one that suits your bolted joint design, metallurgy, coatings and needs of the future

MJCronin
Sr. Process Engineer

Quote (MJCronin)

I disagree with the statements above that "you can drive the costs through the roof" by specifying NORDLOCK devices ... What is the cost when the joint comes apart ?

I'm not talking about that.
Of course you're going to use them if it's critical to use them.

I was just saying that the cost of Nordlocks isn't all that negligible (as opposed to plain washers), so one needs to be mindful of that fact and not use Nordlocks everywhere simply because they exist. :)
Not all joints are critical and not all are in danger of coming apart.

I've seen people stack up thousands of dollars worth of unnecessary cost simply because they automatically assumed washers were cheap (easy mistake to make since 99% of time they are negligibly cheap).

Even with 'snug tight' A325 bolts loaded in tension by hanging mechanical stuff... I still use Loctite Red. Just to be safe.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

MR. MJCronin (Mechanical) has nailed it with his perfect wording.