JonL
Elder Statesman
WWSME (Wiltshire)
Posts: 2,907
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Post by JonL on Dec 23, 2018 20:30:58 GMT
On my Britannia the crankpin for the leading driven axle is described in LBSC's words and music as requiring a 3/32 x 40 thread. As my crankpins were already made (to a good standard it would appear) I'm taking a bit of a leap assuming that the thread is indeed correct.  My daft question is, what thread is this? I've seen 5/32x40 described as a model engineering thread, but this is 3/32x40, and I can't seem to find a die that size or even fasteners. Can anyone shed some light please? |
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mbrown
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Post by mbrown on Dec 23, 2018 21:08:26 GMT
At the time LBSC was writing, I think you could get all sorts of threading gear that isn't available now. However, for 3/32" dia threads, he usually specified 7 BA (itself quite hard to come by nowadays - you can get the taps and dies but the screws to suit are more elusive). 7 BA is about 53 tpi, so it is finer than 3/32" x 40 and probably more fit for purpose.
Depending on when your crankpin was made, I think 7 BA is more likely than 3/32" x 40 - but the only way to check is to find a 7 BA screw and see if it fits. If not, you might have a bit of a job sourcing a 3/32" x 40 screw.... I am not sure what the nearest metric equivalent is, but I'd try 7 BA for starters.
Good luck.
Malcolm
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Post by dhamblin on Dec 23, 2018 21:12:51 GMT
It's 5/32 x 40 on the sketch in ME 2609 (24th May 1951), perhaps the drawing is wrong?
Regards,
Dan
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JonL
Elder Statesman
WWSME (Wiltshire)
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Post by JonL on Dec 23, 2018 21:40:33 GMT
That makes sense, a drawing error does sound quite likely.
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Post by mr swarf on Dec 23, 2018 22:30:17 GMT
Just looked at my set of drawings & it shows it as 5/32 x 40 as well as Dan.
It has been known for people to use 5BA instead as then you can use a 5BA csk screw which are widely available so its worth checking for this.
Paul
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JonL
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WWSME (Wiltshire)
Posts: 2,907
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Post by JonL on Dec 23, 2018 22:31:04 GMT
Thats great, thanks Paul.
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JonL
Elder Statesman
WWSME (Wiltshire)
Posts: 2,907
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Post by JonL on Dec 30, 2018 20:04:46 GMT
I just tried a 5BA tap gently into the hole; it doesn't touch the sides. A bit more investigation with a drill bit shows me a 3.2mm drill bit shaft fits the hole. That does lead me to believe its the 5/32x40 (which is a Whitworth size I think?) EDIT Its an ME size... but I have confirmed its most likely the 5/32 rather than a close BA equivalent.
Thanks to all who helped.
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mbrown
Elder Statesman
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Post by mbrown on Dec 30, 2018 21:57:24 GMT
The ME series of threads are Whitworth thread form - but not Whitworth pitch.
Malcolm
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JonL
Elder Statesman
WWSME (Wiltshire)
Posts: 2,907
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Post by JonL on Dec 30, 2018 22:04:50 GMT
Ok thank you. This really is a minefield for the uninitiated.
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Post by silverfox on Dec 30, 2018 22:48:34 GMT
Tracy Tools in Devon are your friend
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