The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => Lucas, Ignition, Charging, Electrical => Topic started by: TimK on 18.11. 2019 00:17
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Hi Everyone
Does anyone know the thread size of the "coil core locking nut" on the rear of the horn?
Cheers
Tim
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http://taffthehorns.com/
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Without a horn to hand, my guess is that Old Joe Lucas would use a BA (British Association) Thread as this is the common thread favoured at the time for electrical components.
Thread is a basic 47.5 degrees, for all sizes, Largest size (0 BA) has Nominal diameter 0.2362", Minor diameter 0.1890" and 25.4 TPI, ( a real oddball system) The TPI changes for every reduction in diameter. See if your bits are anywhere near to dimensions on published data tables.
Smaller sizes in this system are identified by a larger numerical designation, up to 12BA at 0.0512" nominal diameter, with a TPI of 90.9!
Apologies in advance if I am completely wrong, but it is a good place to start.
Taff the horn is always worth scanning for a little light relief, but be careful working with horns all day........
Swarfy.
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That would be 9/16" x 32 t.p.i.
Just one of the many Lucas bastard threads.
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.......... ...... and 25.4 TPI, ( a real oddball..
That equates to 1.0mm pitch *conf2*
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B.A. is a metric thread, Dutch.
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B.A. is a metric thread, Dutch.
I've long suspected that but never saw it documented.... *conf2*
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http://mdmetric.com/tech/thddat8.htm#ba
There you go DuTch - Doesn't say 'It's a Metric Thread Form' in as many words, but you'll see all the major diameters are roundish numbers/fractions in metric, going down in a series of carefully-planned steps from 0BA at 6 x 1mm.
Spanner sizes which don't really overlap a whole lot with fractional AF sizes, but 4BA is 1/4 AF - and that's the commonest one we need.
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Swarfy,
At my age, it is a while since I had a horn in my hand.
Col
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I thought you were one, Col.
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Thanks guys, it's definitely a bigger diameter than any of the BA options and looking at the thread I'd say that trevinoz's 9/16 x 32 tpi looks a very good candidate.
Cheers
Tim
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http://mdmetric.com/tech/thddat8.htm#ba
but 4BA is 1/4 AF - and that's the commonest one we need.
4BA is considerably smaller than 1/4 AF?
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Yes - but Across the Flats spanner jaw size Rex, not shank diameter . . .
Standard hex on say, UNF or UNC 1/4" screw/bolt, is 7/16" across, which is v close to 3/16" WW - aka 1/4" BSF.
I fully understand why all my mates here where I am are perfectly happy with metric on their 'Continental European' machinery!
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I fully understand why all my mates here where I am are perfectly happy with metric on their 'Continental European' machinery!
*lol*
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........I fully understand why all my mates here where I am are perfectly happy with metric on their 'Continental European' machinery!
Yes true as- but the actual fasteners are not always available from a regular nut and bolt shop either....Auto/Moto threads are usually ISO fine -or ?- instead of hardware coarse eg; Moto G frame joint 12mm x 1.0 (?) socket heads *pull hair out*
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Yes - but Across the Flats spanner jaw size Rex, not shank diameter . . .
I don't know if I'm being particularly thick today, but 4BA is roughly 6.5mm across the flats, and 1/4 UNF is roughly 11mm. :!
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And yup again DuTch, 'tis very true!
There is quite a lot of stuff that's a real pain on some of the classic 'Metric Machines' too, especially a tendency to use 7mm and 9mm, often at 1mm pitch. Your average supplier won't have any of that, is for sure. Not always that easy to find threading tackle for some of the different pitches they used down in the 2.5 to 4.5mm area either.
But . . . at least metric spanners fit all metric bolts, even if the heads are often a size smaller than you'd expect for the shank.
It's not just 'continental' makes either - I cursed for hours when I broke the heads off a couple of undersized 12mm AF (but M8 shanked) seized exhaust header pipe retainer bolts on my XJR Yam a while back. Absolute nightmare to sort out with the engine in the frame, and I ended up making new studs and brass nuts at 13mm AF, which will be a lot easier to get off next time. (Bit like the ongoing sump plate discussion on here . . . Why the heck do people use bolts & setscrews in places where they are almost guaranteed to cause trouble down the line?!) Little Things that can Cause Big Grief, when the manufacturer's consideration only extends to the initial assembly of a new part in a clean factory environment.
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Not thick at all Rex, it's just that these things are designed to confuse!
1/4 inch bolts in UNC and UNF take 7/16th AF spanners - that's yer 11mm near enough - across the jaw. You're dead right. They don't take a 1/4 AF weapon.
But 4BA bolt heads will take 1/4 inch AF - across the jaw - spanners.
A Whit form spanner is sized according to the bolt diameter not the width of the hex head and so the sizes are always miles 'smaller' than spanners for US-type fasteners. Hence the ref to 3/16 Whit or 1/4 BSF being pretty close to 7/16 AF.
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......There is quite a lot of stuff that's a real pain on some of the classic 'Metric Machines' too, especially a tendency to use 7mm and 9mm, often at 1mm pitch.....
I was fixing something for a friend and needed a 7.0mm 1.0 bolt and was surprised the bolt shop had "em in one length ~2"- the guy said they something to do with bicycle seat post
Ok- I don't want to hijack the horn thread...
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Hi Everyone
following up on my original post, I gave up trying to find a suitably threaded locknut ( I though taffthehorn would be my best bet, but he didn't get back to me), but my brother managed to find a tap for me (he makes stuff for aircraft and they use some seriously weird threads in that industry), so I'm going to tap another lock nut to the correct thread.
Cheers
Tim
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So what thread did you end up with ?
Totally unrelated, I needed a M12 *square* nut for a doo-dad for a wing-wong I was making, but gave up and made one *bright idea* from 10mm flat bar *work*, (various websites showed them to no avail *pull hair out*)
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Just to say, a bit late in the day, sorry! - that 9/16" x 32 tpi is an available size. I was on Tracy Tools' site the weekend looking for 19/32nds x 32 - which isn't listed and maybe doesn't exist - and saw 9/16ths (which I do have) is still there. (55°, if it matters, which at that size it probably doesn't, much.)
https://www.tracytools.com/taps-and-dies/whitform-taps-dies?page=2
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My brother is sending me a 9/16 x 32 UNS which he got at mates rates due to the amount of stuff his company buys. I saw the tap at Tracy tools but baulked at paying 9 pounds for a tap I'll probably only use once!