Sizing a jewel from the jewel setting

[ScrewDropper]

As you can hopefully see from the photo, I have removed two cracked jewels from their settings and have preserved a nice sleeve of brass to rub in new ones. The problem I have is that, as is common with cracked jewels, both jewels disintegrated when I pushed them out. I have already worked out the pivot holes from a belt and braces pivot measurement and jewel hole measurement using jewel gauges, before I removed them. The problem I have now is I don't want to start jamming a vernier calliper in the hole to check the jewel size and risk damaging that nice brass lip on each setting and then not be able to rub the jewels back in.  I was thinking of using a pusher to check from the underside and then take the next one up (and so on) from the topside until I find the right fit but was wondering if there is a safer method of measuring or if anyone had any other suggestions, maybe measuring the underside and then adding a tenth or two?

Edited July 26, 2024 by ScrewDropper

[AndyGSi]

What's the movement and what pivots are they as there are some lists showing jewel details for certain movements.

[eccentric59]

If it were me, I'd (gently) slide a smoothing broach into the hole and measure the point where it where it stops. That should get you close.

[ScrewDropper]

1 hour ago, AndyGSi said:

What's the movement and what pivots are they as there are some lists showing jewel details for certain movements.

This is one of those English pocket watches from around 1890-1910. Utilising, from what I can tell, from some geneic parts and hand made. Virtually nothing matches from one movement to another . You get a lot of them on eBay and non have a listed manufacturer. I’m deliberately pushing myself by working with something where I can’t just get parts and have to rebuild anything that is broken but cheap enough that I can ford to fail. I’ve already (nearly, just need to hone the pivots) made a new balance shaft and remade a 3rd wheel staff from another that was too long. It’s a long but enjoyable process 

1 hour ago, eccentric59 said:

If it were me, I'd (gently) slide a smoothing broach into the hole and measure the point where it where it stops. That should get you close.

I can get the hole measurement easily enough by using a pusher from my jeweling set but using it to measure the bed risks damaging the brass lip that I need to rub the new jewel in. There’s some rules of thumb around things like pivot holes being the pivot diameter plus .02mm and I was wondering if there was a similar rule of thrum for the jewel bed

[nevenbekriev]

The rule is that the jewel must get in the bed without resistance and (almost) without free play. So using the pushers is correct idea. Just find the one that will get in as described and see it's size. Be aware that modern levels intended for press fit are not good for rubbing in. They can be used, but after reshaping the outer part like in the old stones

[ScrewDropper]

1 hour ago, nevenbekriev said:

The rule is that the jewel must get in the bed without resistance and (almost) without free play. So using the pushers is correct idea. Just find the one that will get in as described and see it's size. Be aware that modern levels intended for press fit are not good for rubbing in. They can be used, but after reshaping the outer part like in the old stones

This is good advice, thanks. I’m hoping to get hold of some older NoS jewels but I may have to deal with modern(ish) press fit but I’m not familiar with the process of reshaping. Do you have a link to further information?

[nevenbekriev]

Sorry for the delay,

I can say what i do. I turn on the lathe flat the face of a brass rod with a little bit larger or same diameter as the stone.Then glue the stone on the face with shellac and center it while turning the spindle. Then I use diamond file or disk grit 800-1000 by hand to reshape the stone as it turns. Reshape - I mean rounding ор beveling at least on the side where  rubbing will be. Shaping the other side will change the height position of the stone. Reducing the diameter is possible, but not to much as hand filing on lathe sometimes makes things excentric