What size nut?

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Stan

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I have recently acquired a Marples mitre jig, in the original emerald green paint.

20220425_151824.jpg


I'm in the process of cleaning it up so I can use it. ( I will be keeping the original paintwork because it has character ).

The threaded rods that move the jaws have unusual size nuts. Now obviously they are not metric due to when it was made. But to give you an idea of the size they fall between 13mm and 14mm. I have a set of Imperial spanners in increments of 1/16 inch and the nuts come between two sizes there also.

So what size are the nuts, and what measuring system do they use?

Thanks in advance for your help.
 
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Spectric

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In the days before metric you had a choice of UNC, UNF, Whitworth and even a cycle thread at 26Tpi. Those look more specialised, a square profile like a vice.
 

Stan

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20220425_164003.jpg


Not my greatest piece of photography, but the large thread is indeed square section. The bottom of the right-hand bolt shows that the thread is cut for the nut more like a standard thread.

20220426_163525.jpg


Size of nuts compared to a 9/16 spanner.
 

Vann

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...The threaded rods that move the jaws have unusual size nuts. Now obviously they are not metric due to when it was made. But to give you an idea of the size they fall between 13mm and 14mm. I have a set of Imperial spanners in increments of 1/16 inch and the nuts come between two sizes there also...

Although it doesn't say so on the part of the spanner we can see, I assume your spanner is 9/16" AF (Across Flats). What you want is a BSW/BSF spanner - 1/4"W-5/16"BSF to be specific - which should measure 13.34mm AF (though most of mine are worn and some are getting up nearer 14mm).

Note that the size of BSW/BSF nuts is measured by thread diameter, not across flats.
Also note that during the last world war BSW nuts were reduced in size to the same size as BSF - to save material - and to confuse future generations of obsolete thread users ;) .

Cheers, Vann.
 

J-G

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Not my greatest piece of photography,
You're not wrong there! :D

Stan said:
...but the large thread is indeed square section. The bottom of the right-hand bolt shows that the thread is cut for the nut more like a standard thread.
The right hand thread is WORN. They will both be Square thread form and you are unlikely to find Nuts unless they are retrieved from another Marples Mitre Jig. Even sourcing Taps to make your own will be a major problem. At least Square Threads are relatively easy to measure :)

I suggest that the most efficient way forward - assuming that you wish to make the Jig servicable again - (and taking note of the wear) would be to obtain a length of ACME threaded rod of a similar diameter and Taps to suit.
 

J-G

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Re-visiting this question, I'm now of the opinion that you are not talking about a nut for the Square Form Thread but for the end of the part.

The 'Nut' for the Square Form thread will be the 'Jaw' of the Jig. What you haven't shown in your 'Photo' is the end of the part with the nut removed. A close-up photo of that MAY give someone a better opportunity to determine what the thread size & form might be. A guess would be a Whitworth form and most likely a 'Standard' (BSW or BSF) but without a photo which included a 'scale' reference that's the nest I can do.
 

Stan

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Thanks for the above folks.

@Vann - thanks for that. Until recently I never got my head around all the different systems. A lifetime ago I thought my metalwork teacher meant to write "bolt" when he wrote "dolt".

@J-G I am indeed talking about the end nut. Tomorrow I will get a photo. The two bolts in the above photo are a before/after comparison for cleaning it up. The right one still has the crud of ages case-hardened on it. They are both cleaned up now.

I have also cleaned up the machined surfaces using wet/dry paper lubricated with WD40, followed by rubbing wax into them. One jaw works smoother than silk. The other will need further checking - it actually works now and has full travel, but is too stiff.
 

Stan

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20220427_105123.jpg


Better image of the "business end". ( scale in inches ). Mystery is solved - I bought a set of Whitworth spanners and the nut is a perfect fit for the 1/4W.



Renovation now complete. Works beautifully. Posed next to the plastic mitre box ( ugh! ) it will replace.

20220427_105639.jpg



Is this modern progress?
 

clogs

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Stan,
to replace ur jig like for like would cost a fortune...cast iron.....in excess of £300 a pop...
the wood then plastic ones were ment to be thown out when worn....
still have my dads beech wood mitre block....
 
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