Fitting jewels when the hole for the mainspring arbour is worn

[Paul80]

Hi all.

I see that it's quite common when faced with a worn hole were for example the mainspring arbour rotates for the warn hole to be enlarged to fit a jewel to bring the hole back into tolerance.

The question is, what's an acceptable way to enlarge the hole so the a jewel can be fitted, I assume just drilling it is not accurate enough as drilled holes are never exactly round.

What method do you use ?

Thanks.

Paul

 

[mikepilk]

I use the reamers with a jewelling tool to enlarge the holes.

I've never managed to repair barrel arbor holes with jewels. Have you checked that you can get jewels of the correct size?

Seiko's often have a worn bush on the bridge side of the barrel arbor. It needs a jewel with about a 1.4mm hole. The biggest I can see on Cousins is 1.1 mm (and the brass bushes only up to 1 mm hole). Also the bridge is often not deep enough to take a friction fit jewel. Unless it is bushed, and you can get a replacement (or make one), I end up swapping the bridge. 

 

[JohnR725]

9 minutes ago, mikepilk said:

I've never managed to repair barrel arbor holes with jewels. Have you checked that you can get jewels of the correct size?

I have this vague memory that's I've seen a picture of students in school who learned how to make bushings. So whether exercises is to make a new bushing for the mainspring barrel but I can't remember if it's for the main plate or and the barrel?

Then yes jewels are nice but they're only nice if they're the right size. In addition to the diameter size they would have to be the right thickness size you get bigger diameter jewels that are usually thicker they might not actually fit at all.

This is where American pocket watches that had jeweled bearings the barrels are usually designed differently so they can have much Thicker jewels

[mikepilk]

1 hour ago, JohnR725 said:

This is where American pocket watches that had jeweled bearings the barrels are usually designed differently so they can have much Thicker jewels

That's why I love those American pocket watches - designed to last. The problem is finding replacements when the jewels crack.

I have a 16s Elgin Veritas with 23 jewels - running great after 100 years !

[JohnR725]

3 hours ago, mikepilk said:

The problem is finding replacements when the jewels crack

It's where you have to make an assessment as to whether the crack is a problem. A lot of the watches use natural stones they do have flaws they have cracks but the cracks have been there since the beginning of time they do no harm.

This is where someone new to pocket watch repair sometimes in the discussion group will point out oh dear all of my jewels are bad. Then no attempt to replace all of them which is basically going to be impossible. You basically have to look at every single flaw look at how and where it is and how it looks in the hole itself. If it's not a problem they are it's not a problem other then you will be upset because you think it's a problem.

Unfortunately this doesn't always work for balance jewels they usually get impact damage and then they are damaged And then the hole itself for the balance pivot is no longer round. A lot of times the pivot itself is no longer round or smooth either is very visible at everything is very bad.

 

[mikepilk]

4 hours ago, JohnR725 said:

It's where you have to make an assessment as to whether the crack is a problem.

I agree. This is the jewel on the end of the barrel arbor of my Elgin Veritas. It is chipped, but works just fine, so no need to replace (even if I could find one)

Edited January 23, 2022 by mikepilk