Nut screws washer and bolts

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Kiwi Bloke 1 on 26/10/2018 08:55:12:

… I started the thread in the hope that it would get people to think.

Thread-locking compounds are probably the answer… ; )

.

I did think … and remembered that, in the vibration test-house we never used, or recommended the use of, any form of spring lock-washer.

[the exception that proves the rule being the Earthing point which someone referenced earlier]

MichaelG.

[Tim StevensParticipant @timstevens64731]

Ian – the thin lock nut does not 'become a washer' as you suggest, it should be locked by tightening against the thicker outer nut, so that in the event of the system developing slackness (no load on the bolt/stud itself) the two nuts remain in place.

The 'correct' placing of the thinner nut was a concern from the beginning of last century at least. I quote from the ICS Reference Library Textbook on Machine Design (vol 5) 1907:

A common device is the locknut … Two nuts are used, one of which is about two thirds the thickness of the ordinary nut. The load comes on the outer nut, which should therefore be the thicker one. In practice, however, the thin nut is usually placed on the outside, because the spanner is generally too thick to act on it when placed below the other.

So there, great-grandad was right all along … And of course, spanners are now made of alloy steel and can be much thinner, removing any excuse for not doing it right.

Tim

[HopperParticipant @hopper]

This document outlines current science in a plain and interesting way. The two graphs at the bottom show results from a Junkers vibration tester and seem pretty conclusive. The do make the proviso that the thin-nut-first method while locking better, requires more time consuming and more skilled assembly. **LINK**

Yes, methinks Loctite etc is the truly modern way to go, so all this is a bit academic. I can't think of anywhere I've actually seen double nuts used except on vintage machinery, where period-correct assembly is the "wrong" way round with thin nut on last.

Edited By Hopper on 26/10/2018 12:33:37

[David TParticipant @davidt96864]

Posted by Nigel Bennett on 24/10/2018 14:31:30:

Possibly David T's application wasn't suited to the way they work – the hardness (or otherwise) of the mating materials can upset them. Did you try approaching Nord-Lock themselves for advice, David?

Hardness may well have something to do with it. Our application includes securing a crimp to maintain electrical continuity, so a relatively soft material is involved. I don't know if Nordlock were ever contacted to begin with as they were introduced before I moved into my current job.

[Ian S CParticipant @iansc]

In one artical I read that the thin nut on the bottom should be softer than the full nut.

In one of my books the method of assembly is, tighten down the 1/2 nut and hold with a spanner, tighten down the full nut, then hold the full nut and back off the thin nut against the full nut

Isn't Loctite great.

Ian S C

[Eddy CurrParticipant @eddycurr38053]

A Thank You and some comments.

That 1/2 height Jam Nuts function better underneath full height Hex Nuts than on top comes as news to me – I have never seen an OEM configuration where the Jam Nut wasn't on the outboard side of the thread. However, I have since seen some authoritative reports confirming that an inboard placement is superior. Thank you for drawing this to my attention.

On my side of the pond, there are names for thin wrenches/spanners intended for use on Jam Nuts. Stanley Proto offers the following:

– Check Nut Wrench: Single, open end wrench with head set at a 15° angle

– Service Wrench: Single open end with head set at a 30° angle

– Tappet Wrench: Double open end with heads set at a 15° angle

Regarding Pal Nuts mentioned earlier. The unknowing should be made aware that the formed from stamped sheet metal Pal Nut is physically different from the machined from solid bar stock Jam Nut.

Regarding Nylok Nuts. The nylon locking component is not suitable for use in elevated temperatures – one example stipulates a ceiling of 140°C (284°F) in ideal conditions. There are specials rated for higher temperatures, but the improvement is insufficient for many applications.

An alternate form of self-locking nut that is suitable for much higher temperature service is the Stover Nut. The outboard side of a Stover Nut is intentionally deformed after threading, this creates an interference fit between the nut's deformed threads and those of a bolt or stud. Stover Nuts are reusable.

Lastly, an reference source for fasteners.

"Nuts, Bolts, Fasteners and Plumbing Handbook" Smith, Carroll

Most recent edition: http://carrollsmith.com/books/nutsbolts.html

[Bill PudneyParticipant @billpudney37759]

Where I worked in the 80s at a company making electronics for the defence industry, company standards insisted on using wavy washers, under every fastener, bear in mind these were all small fasteners under about M5. There had long been a feeling that wavy washers were a waste of time, but the standards stood. Then I saw an electronics box, full of PCBs and other stuff, all held together with an approved fastener scheme on a shake table. It only took a minute or so for the screws to start to release, and about 3 or 4 minutes for most of the screws to fall out.

We still had to use wavy washers though, but on final assembly we started using Loctite.

I will continue to put full size nuts on first, and locknuts last.

cheers

Bill

[Alan Waddington 2Participant @alanwaddington2]

30 years ago i had a short stint selling nuts and bolts, around that time Unbrako brought out a product called Durlok, which were nuts and bolts with a serrated flange built in.

They worked really well, i sold loads to local stone crushing plants that had battled for years with bolts coming loose. Also picked up a large order from a bus manufacturer who used them for bolting in seats, which had previously worked loose over time when fitted with all manner of traditional fasteners.

They were a brilliant and simple idea, however the cost was eye watering, which is probably why they never took off in the mainstream.

[Howard LewisParticipant @howardlewis46836]

I remember Durlock setcrews and bolts. They were extremely difficult to undo, The "ratchet" serrations under the head really worked. Once tightened, you never needed to worry about them slackening.

Howard

[BazyleParticipant @bazyle]

The airborne electronics I made used wavy washers typically on M2.5 screws and they survived the random vibrator that was driven by its own 1 megawatt generator for a 1 hour test. I can't remember for certain but I think we used Loctite on the satellite flight hardware. An Arianne rocket vibrates harder than a Harrier during take off but only does it once and it is kind of hard to check if any of the screws came loose.

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