Pivot Size V's Jewel Size

[mistergrumpy]

So, my first question. Already did someone ask? Well yes, I'm stuck already. 

I'm playing with a no name pocket watch movement that must have came in a bundle of others and it needs two jewels and then should run again.

I'measured the pivot size with vernier calipers at 0.2mm and coincidentally have a packet of 0.2 and 0.22mm Seitz friction fit jewels that I bought new from Cousins towards the start of the year for another job (a nice Thomas Russell) now before I press them in I thought I'd try the pivot in the jewels to check it wasn't too tight (hence the reason for having both sizes in the first place) and the pivot doesn't fit either size, not even tightly, it's too big. 

I tried sitting the pivot into a 0.2mm stake and it fits great but not in the jewel. Am I missing something? I can't understand what's going on. I'd prefer not to buy more jewels at £15 for 3 and then delivery, which I recall being around £5 takes the price way over the value of the movement. Bushes are sold in 10's and are even more expensive. Shame really.

Anyway, thanks in advance.

[szbalogh]

You can polish a bit from the pivot or widen the hole in the jewel

[david]

Grumpy,

From your information it looks like the pivot is .1mm too large for the jewel hole. The pivot is almost the proper diameter and needs to be brought down slightly to the final diameter. This is a job for the Jacot tool.  Using a Jacot tool with the Jacot drum and  burnisher will bring the pivot down to the proper diameter and finish. There are other ways to do this such as using a flag tailstock center and wig wag with your watchmaker lathe, but for this application the Jacot tool can produce a great result.

david

[mistergrumpy]

SZBalogh I've seen your home made Jacot for polishing. I know I can widen the jewel hole with diamond paste but I thought I'd have to get it on the pivot and turn it in the jewel first.

David, out of interest why do you say 0.1mm? I'm thinking you're actually right but just wondered if you knew something I didn't (it's highly likely actually). As above I guess the Jacot is the way to go, depends on the price versus new jewels but then I suppose it'd come in useful in the future.

Thanks fellas. I don't understand what's gone wrong in the first place.

[david]

Grumpy,

Yes, that is .1mm or 1/10 th of one millimeter. It is about .004 inches or roughly the diameter of a human hair. The difficulty comes in due to the metal becoming weak and breaking under the cutter pressure. With the use of a Jacot tool the cutter (burnisher) pushes the pivot into the grove in the Jacot drum where it is supported while it is being machined.

By the way nothing went wrong. Parts sometimes need to be adjusted and modified in order to work properly. As we do more of this, skills are learned and knowledge is gained making this an ongoing process. Everybody who does watch repair has to go through this. If you try something and fail and then learn from it, then you have experienced a great teaching tool.  Enjoy the journey.

david

[david]

Grumpy,

I just took another look at your dimensions. My mistake, it needs to be reduced by .01mm not .1mm. 

david

[mistergrumpy]

Ah that makes more sense. 

[syfre]

pivot size are measured in 1/100 of mm ; example a pivot of 18 means 0.18 mm ; you need a jewel hole just larger than the pivot ; example for a 0.18 pivot you need a 0.20 jewel hole

Also : to measure a pivot you need a pivot gauge or a (good) micrometer; you need measurement at 1/100 of mm.

Have a look here :

http://www.awci.com/wp-content/uploads/ht/September2011.pdf

[mistergrumpy]

syfre. Yes, the problem I had in the past is what you say, I didn't allow the 0.02mm oversize. With this watch I measured the pivot at 0.2 and so chose a 0.22 jewel but it won't even go into the hole which confuses me. As ever a constant challenge for me is, as you point out, measuring the pivot. My vernier caliper showed 0.2, I have a micrometer from Cousins but it's cheap junk. That's why I checked the caliper measurement against the stakes (as gauges). I've seen the Seitz pivot gauges but they're few and far and a bit expensive. I need to see if there's any none Seitz gauges.

[syfre]

look at this post :

there is a pivot gauge with the Jacot ; an other option is a good micrometer (a mitutoyo for example) with 1/1000 resolution

[mistergrumpy]

Thanks again. I'm on it. I'm not allowed to buy myself anything at the minute because it's my birthday on Sunday so everything's a gift idea for someone (and I'm skint!)