That's all OK until you dismantle the joint, whereupon unless careful measures are taken, the full tension of the joint may be taken on the half nut as the full nut is removed.

Bob

So how does a counter nut work, as it goes on top of the full nut?

Andrew

The usual justification for putting the thin nut on top is purely practical – otherwise a very thin spanner may be required. This is not valid if the thin nut is tightened first, etc…

re – measuring the tension in the bolt: Triumph motorcycle big end bolts (5/16" or 3/8" dia.?) were tightened to achieve a specific elongation, and hence clamping force, of the bolt. I may have more detail on that, but is a bit late for crawling about in the attic.

The much bigger sizes used bolt heating is used to lengthen the hollow bolt and the subsequent cooling tightens it. In steam chests at close to 565deg C the stud-bolts are hotter than the heaters can achieve. There is a variety of "patent" nuts for high pressure applications, including hydraulic stretching, out there. Someone with recent experience in petro-chem might be able to expand (sorry) on this.

All of this is technically interesting, but of little relevance in model engineering.

I agree with Duncan.

The late great Tubal Cain (T Walshaw) discussed this in the ME and proved that the thin nut goes on top.

I have worked in engineering all my life and have never seen any practical installation of a thin nut first then big nut, that's not to say somewhere there is an example.

This topic always seems to come up every few years! But I will go with the vast experience of Tom Walshaw and say big nut first then thin locknut on top!

Regards

Derek

Nipping back a couple of years, to the thread that I linked last night … I have an hypothesis:

The long nut is being used because it provides a long ‘bearing’ and keeps the load axial

… a shorter nut in that position would cant over; introducing stress concentration in areas of the thread, and localised loading at the nut/washer interface.

MichaelG.

.

Edited By Michael Gilligan on 19/12/2021 09:28:42

I can't claim any personal expertise in this area but I am with the "thin nut on top" school because of Tubal Cain's explanation which included the fact that the bolt stretches and the nut compresses as the assembly is tightened. This factor, which renders most of the simple explanations void, is strangely missing from many of the counter arguments in previous posts.

Tom Walshaw ( Tubal Cain) worked in the heavy engineering industry most of his life until he became an academic and professor of applied engineering in later life. His analysis is good enough for me.

Rod

Sorry, just noticed Gary's post which I had not seen when I was typing mine, I agree with him .

Edited By Rod Renshaw on 19/12/2021 10:44:39

I turned to, and cite below, one of my old handbooks written for professional machinery designers and engineering-degree students way back last Century, historically closer to what much model-engineering and model-engineering workshops replicate. Notwithstanding any sophisticated modern developments in aerospace engineering and the like – though very important in their spheres they are not necessarily relevant to our work.

It shows three practices (also assuming a vertical stud pointing upwards, for simplicity):

d = stud diameter. Half-nut depth = 1/2 d. Full nut depth = d.

Italics denote quotes.

A) Half-nut below the full nut.

B) Half-nut above the full nut.

C) Two equal-sized nuts each of reduced depth = 2/3 to 3/4 d.

'

A) is described as the correct practice,

B) is faulty but common for practicality – and only because … spanners are rarely thin enough... !

C) allows practicality especially where there is insufficient clearance for two full nuts as was sometimes used – although that also … offends the eye… we are told. Indeed it does!

'

The rationale, copied verbatim, my using bold for the original's italics:

… a little consideration will satisfy the student that is is the top nut which takes practically the whole load, so of course the thick nut should be there as the true lock nut…

So you must decide for yourself for your own project, really, since as like as not the trade-built prototype may have been "wrong" too – or more likely we see preserved examples re-assembled "wrongly" after overhauls – but that's not really an excuse when the fastenings are fully exposed, as on a marine-engine, locomotive or traction-engine.

Make the few thin spanners needed, from gauge-plate? Or mill down some low-cost commercial spanners?

If you making non-model equipment, e.g. workshop equipment or miniature-railway rolling-stock of purely functional form, by all means use alternatives such as insert-nuts.

++++

One of the diagrams also adds a root-diameter extension to the stud, approx. d/3 high, to take a split-plin for added security. The reduced diameter also helps you locate the nut on the stud, especially in a confined space. The extended stud is shown with a somewhat flatter end than the others, and its thread not protruding above the nut.

Useful knowing such proportions in fine-scale replicating.

'

Reference:

Machine Design, Construction and Drawing. Henry J. Spooner, C.E.; pub. Longmans, Green & Co, London, 1913.

It may be 100 years ago but the general theory and practice of bolts, studs and nuts have not changed in that time, save for detailed developments such as plastic-insert nuts and specials for particular trades or very exotic applications.

(When your model-engineering is concerned with replicating very old machinery, or using very old machine-tools, it is worth seeking out these old text-books written for the industry. Although we often make compromises on materials etc. for building methds, function and safety, such books are a valuable repository of contemporary detail practices, component proportions and calculations, etc.)

Edited By Nigel Graham 2 on 19/12/2021 11:44:27

I too am sticking with the thin nut on top.

I don't care how efficient the arrangement is in theory, but if the full size engine I am building a model off uses it, then I will as well just so it that it appears true to prototype.

If I am designing something myself, I will use a modern self locking type nut by choice. I have designed machinery at work for over 33 years and in all that time have never needed to use two nuts on anything.

Phil

I'm also a member of the thin nut on top brigade…..

For a laugh,

when I was in development of wind turbines we reg used bolts over 50mm in dia…

all were hand made with x ray testing etc etc….we used geared nut driver heads/torque multiplier's…..

often over hundred of lbs/ft….

no need for any kinda lock nut….we just relied on bolt stretch…..

ps… some of the bolts were 1.5m long….

.

Especially in Wales

MichaelG.

[ sorry, Howard … I couldn’t resist that one ]

It would appear that both ways are correct under certain circumstances. Bolt Science locknuts
I have obviously been doing it wrong all my life, but then it hasn’t caused a problem so may be over engineered it most cases.