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Norton Atlas tach drive

Norton Models (not Commando or P11)

Norton Atlas tach drive

Postby drp » Thu Apr 13, 2017 8:45 pm

The threads where the cable screws onto the tach drive on my Atlas are boggered up and I'd like to try salvaging it rather than buying a new drive.

Does anyone know what the thread size and pitch is?

Thanks

Dave

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Re: Norton Atlas tach drive

Postby kernel65 » Fri Apr 14, 2017 3:24 am

I was once told 1/2 26tpi Whitworth.
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Re: Norton Atlas tach drive

Postby dynodave » Fri Apr 14, 2017 5:04 am

+1
1/2" measured .493" & 26tpi with pitch gauge
http://www.tracytools.com/taps-and-dies/cycle-%20taps-dies?product_id=975
whitworth ?
then try here:
http://www.tracytools.com/taps-and-dies/whitform-taps-dies?product_id=1098
Tried my 1/2-26 die (sold as CEI) and it barely scratched a hair off the tach gbox.
Last edited by dynodave on Fri Apr 14, 2017 3:39 pm, edited 1 time in total.
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Re: Norton Atlas tach drive

Postby Rohan » Fri Apr 14, 2017 2:43 pm

+1 also.

With the important note that there is nothing 'Whitworth' about it,
it is 26 tpi Cycle Thread.

Americans generally just don't seem to understand British thread systems,
and how there are a number of such systems that share ONLY the hex/nut sizes....

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Re: Norton Atlas tach drive

Postby L.A.B. » Fri Apr 14, 2017 3:24 pm

Rohan wrote:With the important note that there is nothing 'Whitworth' about it,
it is 26 tpi Cycle Thread.



Actually is 1/2 - 26 Whitworth thread.

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Re: Norton Atlas tach drive

Postby kernel65 » Fri Apr 14, 2017 6:51 pm

Rohan wrote:Americans generally just don't seem to understand British thread systems,
and how there are a number of such systems that share ONLY the hex/nut sizes....


Absolutely... Let's call it "discovery learning" when I bought my first tap and die set. Very few true Whitworth uses on these bikes. Andy from Vintage British Cables helped me out with understanding cables and the fixing for them.

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Re: Norton Atlas tach drive

Postby Rohan » Fri Apr 14, 2017 10:44 pm

This is a voyage of discovery !

L.A.B. wrote:Actually is 1/2 - 26 Whitworth thread.


Where findeth ye that diagram. !?
And, who drew it - and is it likely to be accurately labelled ?

Now, everyone knows that that 1/2" Whitworth is 12 tpi, so what is one with 26 tpi called ?

Now2, my tacho drive is brass, so is it 26 tpi brass thread ??
Which could only be, very loosely. referred to as a 'whitworth' thread.
(whitworth must be one of the most loosely used technical terms in the english language.)

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Re: Norton Atlas tach drive

Postby L.A.B. » Sat Apr 15, 2017 2:22 am

Rohan wrote:Where findeth ye that diagram. !?


In a Smiths catalogue.

Rohan wrote:And, who drew it


I don't know. Probably not Mr Smith.

Rohan wrote:- and is it likely to be accurately labelled?


As it's in a Smiths publication then I'd think there's a reasonably high chance it's accurate.


Rohan wrote:Now2, my tacho drive is brass, so is it 26 tpi brass thread ??
Which could only be, very loosely. referred to as a 'whitworth' thread.



'Brass' thread has a 'Whitworth' threadform. Note the term "WHIT. FORM" on the drawing. If it has a Whitworth threadform then it can't be 'Cycle' thread.

https://en.wikipedia.org/wiki/British_Standard_Brass
http://www.britishfasteners.com/threads/bsb.html
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Re: Norton Atlas tach drive

Postby Rohan » Sat Apr 15, 2017 1:41 pm

If it has 26 tpi, then its not part of the recognised Whitworth thread system !!

Now, I have a part set of Brass Thread taps and dies, 26 tpi.
55 degrees, not the 60 degrees of Cycle Thread.
Model steam engines, etc.
Although 1/2" is a bit bigger than usual.
Although maybe not for tacho drives.

I notice the speedo drive uses a different size thread.
What would that be. ?

BTW, I notice too than an Atlas tacho cable uses about exactly the same cable as a
prewar Norton speedo drive (off the front wheel). Same fittings, same length ?

PPS. Perhaps we should ask if UNF and UNC have the same 'thread form' ?

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Re: Norton Atlas tach drive

Postby L.A.B. » Sat Apr 15, 2017 2:48 pm

Rohan wrote: If it has 26 tpi, then its not part of the recognised Whitworth thread system !!


As already stated, it's Whitworth thread form.



Rohan wrote:I notice the speedo drive uses a different size thread.
What would that be. ?


Depends which "different size" you mean?



Rohan wrote:PPS. Perhaps we should ask if UNF and UNC have the same 'thread form' ?


And why would "we" need to ask that?

http://www.britishfasteners.com/threads/unf.html
UNF
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http://www.britishfasteners.com/threads/unc.html
UNC
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Re: Norton Atlas tach drive

Postby bad_friday » Sun Apr 16, 2017 1:04 am

I've found this.

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There seems to be a difference between 1/2" BRASS and 1/2" CEI

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Re: Norton Atlas tach drive

Postby L.A.B. » Sun Apr 16, 2017 1:42 am

bad_friday wrote:There seems to be a difference between 1/2" BRASS and 1/2" CEI


There is.
'Brass' is 55-degree thread.
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CEI/BSC or 'Cycle' is 60 degree.
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Re: Norton Atlas tach drive

Postby acotrel » Sun Apr 16, 2017 6:16 pm

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Re: Norton Atlas tach drive

Postby drp » Thu Apr 20, 2017 2:31 am

Thanks to everyone who responded. Bought a die for $29 (1/2 - 26), chased the threads and I have successfully salvaged my Tach drive

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