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clevtrev

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Magnetoman said:
Now that I'm back from my latest trip I looked again at the drawing you attached and it's worthwhile pointing out it is not metric. It's French metric. What we've known as metric for the past 50 years is an ISO standard introduced c1965. Prior to that the Japanese, Germans, French, and others had their own variations on metric, many of which corresponded to the later ISO version, but some of which did not. As a case in point, the 2mm x 0.45 that Smiths used in this Chronometric drawing is not an ISO metric standard, but it is a pre-'65 French metric standard (the ISO standard pitch for 2 mm is 0.40 mm).
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Suggest you look at the ISO Metric fine charts.
http://www.cign.org/isometric.html
 
Magnetoman

Magnetoman

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clevtrev said:
Suggest you look at the ISO Metric fine charts. http://[/QUOTE]
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http://[/QUOTE] Note that on that page it says "The table above shows MF for metric fine which is not standard."

Actually, ISO "metric" is a moving standard. I have several editions of 'Machinery's Handbook' to refer to because old threads are not necessarily the same as current ones. The edition in my office is the 24th (1992), but at home I have both a newer edition and one from the 1950s that I bought to have information on threads that are no longer covered in the handbook. For example, the German Loewenherz threads -- their version of BA -- used by Bosch in early magnetos.
 
Magnetoman

Magnetoman

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Dinny said:
When is French metric not metric? It certainly is not BA.
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I hesitate to mention this, but BA is metric. The reason for the uncertainty whether the particular Chronometric stud is BA or "metric" isn't because there is an accidental coincidence of similar sizes, it's because 0 BA is precisely 6 mm with precisely 1 mm pitch. They only differ in thread form and angle. According the the British Standard adopted c1900 the pitch of BA fasteners is 1 mm x (0.9)^(BA#), so there is a geometric progression of pitch as BA # changes.

Hence, there is metric, French metric, Loewenherz metric, geometric metric, ...
 
Dinny

Dinny

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Magnetoman said:
I hesitate to mention this, but BA is metric. The reason for the uncertainty whether the particular Chronometric stud is BA or "metric" isn't because there is an accidental coincidence of similar sizes, it's because 0 BA is precisely 6 mm with precisely 1 mm pitch. They only differ in thread form and angle. According the the British Standard adopted c1900 the pitch of BA fasteners is 1 mm x (0.9)^(BA#), so there is a geometric progression of pitch as BA # changes.

Hence, there is metric, French metric, Loewenherz metric, geometric metric, ...
Click to expand...


Ah but as an engineer, a BA nut should be used on a BA stud and the same for metric. In my eyes anything else is a botch.
Interestingly I've never have a speedo fall off my vin whilst riding and I can confirm my nuts are not French.

Everything aside, good luck with the rebuild Dean we seem to have had some drift but at least you can now mount your speedo..
 
greg brillus

greg brillus

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Have you lot seen those Helicoil repair kits made especially for Chronometrics....they are the ones specifically for all your stuffed nuts...whether they're geometric or if you live in New Zealand they're geothermal....it's all beyond me...!!;)
 
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