Finishing pivots

NigelW

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Jan 2, 2015
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My inexperience in horology is taking its toll. Yesterday I nearly ruined my third attempt at making a replacement arbor with integral pinion when turning the pivot on one end. Fortunately my tutor stepped in to help.

The arbor is made of silver steel. I left the pivot oversize when I hardened and tempered it (bound it in soft iron wire, soaped it, heated to cherry red, plunged in cold water, polished off the oxide then tempered it to dark blue). I used an HSS graver to turn the pivot down to size. It was still a bit rough so I had a go at it with a diamond file then a pivot file but ended up making it worse and somewhat oval before crying "Help!".

My tutor took over. He very carefully turned it down to true it up with a very sharp graver and then used the pivot file on the lathe using a runner to support it. It is now perhaps a tiny fraction on the small side but no so much that the hole in the plate would need bushing or the arbor repivoting.

His advice was never to use the pivot file unless and until the pivot is properly true and to do so in the lathe rather than (as I did) on the bench rotating it with one hand while using the file in the other.

Finishing pivots properly is clearly a skill I need to acquire sooner rather than later as I have many to make; any other tips would be most welcome.
 

gmorse

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Jan 7, 2011
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Hi Nigel,

...and then used the pivot file on the lathe using a runner to support it.
This supporting runner is the crucial part, and is the basis of the Jacot tool. It gives you the best chance of producing a pivot that's parallel and concentric, and allows you to apply sufficient pressure on the pivot to burnish it.

Regards,

Graham
 

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