Which ME screw thread

I have been building a little Stuart model and they seems to pick rather odd threads, e.g. 5BA and 7BA. When it comes to the steam
unions it suggests 1/4" by 32tpi ME thread. Yet again its one I don't have a die for (though I have 1/4" by 40). Is this Stuart encouraging me into strange sizes so they can sell me connectors, or is there some logic to these threads - like I should use 32tpi for brass and 40tpi for steel to ensure a decent purchase ?
I looked at MACC engineering supplies and they provide 1/4" union nuts for the 40tpi, but not 32tpi.
Steve (Cheshire)
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At best, we live in a world that has moved away from what was classically the norm. Today, I am just as screwed(?) up as most over fastenings which are fitted to my machinery. You are far more fortunate that you can change the drawings. Most are not written in tablets of stone and unless you are an utter stickler, you can go to metric which is the coarser thread system.
Frankly, I would go for what is still available in the Imperial System ie the 40tpi. If the old BA stuff is not available, you are stuck with metric replacements.
It is worth looking at what George Thomas had to say in Model Engineers Workshop Manual about 'the changes' True, I am a bit biassed towards him but you will glean the possible replacement sizes which he gives.
Digressing further! Like many people who are motivated by the joy of model engineering rather than greed, I was instrumental in publishing old articles from Model Engineer. I had the set of Martin Cleeves articles on Making Socket Headed Screws to post.
Of course, Cleeve is dead or should I say, Hart, but Magicalia who now own ME and MEW have demanded that all old articles be removed from the net. In another site, the present editor is trying to find the next of kin. to him and many others.
As a ME and MEW, contributor of the past, I'm a bit like John Inman in 'Are You being served'
I'm Free!
Norm
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[snip]

As do most suppliers who serve the model engineering market.
Incidentally, 5BA and 7BA can be very useful if for no other reason than they are very close to standard Imperial stock size rod. For all practical purposes 5BA is 1/8" diameter. 7BA is only a few thou' away from 3/32". <http://shopswarf.orcon.net.nz/ba.html
--
Mike Hopkins
CSME <http://www.cheltsme.org.uk>
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Mike Hopkins wrote:

Thanks Mike,
So maybe using odd numbered BA sizes isn't so strange, I thought most people only used the even numbered ones - maybe thats just electrical practice.
I'll use 40tpi for the unions, its not a scale model, so thats not an issue. I just wondered if the 32 and 40 were like Whitworth and BSF respectively (i.e. whitworth in soft metals and cast iron, BSF in steel).
My next model is to 1/12th scale, but the drawings are metric with metric threads - as I don't have metric screwcutting, I thought I would try for scale threads. I was going to work out the nearest imperial size, calculate the thread, and then find the nearest scale thread. But its 1/12th scale, so even 4 tpi, becomes 48 tpi. Scary - I hadn't worked it out until now !
I suppose all but the purists compromise quite a lot.
Steve
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[snip]

Scale threads? Scale hexagons? The pitch of each BA screw is approximately 90% of its predecessor in the series and the relationship between pitch and diameter remains mechanically sound throughout the range. That means that in 'our' sizes you can always find something that is so near scale that the eye is unlikely to detect any difference. Also BA is still widely available commercially (at least in the UK) and specialist suppliers such as EKP go one further and offer choices of hex head and nut size.
--
Mike Hopkins
CSME <http://www.cheltsme.org.uk>
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Mike Hopkins wrote:

Thanks Mike.
I suppose the only problem with BA is if you need to screwcut a thread, but I am realising that once you have enough dies, then that is no longer an issue - and my set is nearing completion, and they are not too expensive (provided you buy carbon steel and one at a time).
My grandfather did some model engineering and he made taps and dies to scale so he had scale threads - my father has them. I get the feeling like this was a bit OTT - I will settle for something less ambitious for now.
Steve
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Not really. It just depends on the application. Modelers trying to get close to scale dimensions of small union nuts might go to 60 tpi even. On the other hand, where a good strong fixing is needed and scale is not so important, 26 tpi (brass gas thread) can be used.
--
Charles Lamont

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Re: Which ME screw thread
When my Father was apprenticed at Stuart Turner in the 1920's they use 1/8" Whitworth as their preferred size. 1/8" Whit is 40 TPI, which i also the same as the generally used ME thread TPI, but 32 TPI is als an ME thread!!
32 TPI ME thread is normally used on sizes of 5/16" and above, but t muddy the waters some more, 32 TPI is common on small UNF/UNC sizes!!
If you want to know where different British threads came from start b following this link to Joseph Whitworth who started it all.
http://en.wikipedia.org/wiki/Joseph_Whitworth
As for odd size BA threads, 3, 5, 7 etc, these were origianlly mostl used for electrical connections as a safety precaution, with the hop that as the threads are not generally compatible with non electrica parts people wouldn't be able to make 'inappropriate' connections!
If you need taps and dies for ME and BA sizes you could try Trace Tools in Dartmouth who I've always found helpful.
Joh
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jlh45 wrote:

John,
I actually have the original article in an 1842ish copy of Practical Mechanics. Very interesting - I thought he calculated what the required thread was, but not so, he actually went around the country finding what threads people were making in different sizes and worked out a statistical average. I also have an article and the designs for Joseph Whitworth's lathe, and you can see all the elements of a modern lathe are there. He was one of many very clever Victorians. Those were marvellous days to be an engineer.
Steve
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Odd numbered BA threads were quite common in small engineering eg model aero engines, etc as well as steam. Even numbers prevailed in electical circles. 32tpi WF is the standard for ME threads. They're all still pretty much available, try Tracy Tools if you get stuck.
Whilst I do like the standardisation of metric per se for production purposes, they're not nearly such 'nice' forms and not nearly so varied thus reducing the opportunity to select 'just' the right one - admittedly more from and aesthetic perspective than a tehnical one.
Richard On Thu, 14 Jun 2007 00:11:57 -0700, Cheshire Steve

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Richard wrote:

> > The RR engine I've got apart at present had approx 70 1 BA studs holding the inlet manifolds together. :-(
Tom
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