Jeweling of mainplate “edge-type” jewel bearings: commonly found for third wheel jewels

[ifibrin]

Just curious, but how is the jeweling done for mainplate “edge-type” jewel bearings, commonly found for third wheels? The jewel is not typically held in a full hole on the mainplate, but on a U shaped crescent in the mainplate. This would appear to make it quite difficult to support on the stump of a normal jeweling tool (either Horia micrometer type or lever-type).

 

[nickelsilver]

It can be pushed out and in just fine with normal stumps and pushers. The seating in the plate is machined during manufacture with a 3 point hold, there's no way to ream a partial hole like this.

[ifibrin]

1 hour ago, nickelsilver said:

It can be pushed out and in just fine with normal stumps and pushers. The seating in the plate is machined during manufacture with a 3 point hold, there's no way to ream a partial hole like this.

Does that mean finding the right jewel to replace it has to be very exact? Usually when replacing a jewel you sometimes have to use one that is slightly bigger and broach the hole to get it to fit? Because you can’t find the exact same size one for both pivot and jewel size. At least that’s what I thought...

[clockboy]

I have never seen that before. If it is correct what a poor design. 

[ifibrin]

8 minutes ago, clockboy said:

I have never seen that before. If it is correct what a poor design. 

It’s usually seen in lady’s watches... This is an ETA 2671.

[nickelsilver]

39 minutes ago, ifibrin said:

Does that mean finding the right jewel to replace it has to be very exact? Usually when replacing a jewel you sometimes have to use one that is slightly bigger and broach the hole to get it to fit? Because you can’t find the exact same size one for both pivot and jewel size. At least that’s what I thought...

Yes, it would have to be exact. First of all, it uses this poor design (as Clockboy rightly says) as there is only space for that size jewel, with that odd mounting, there. And there would be no way to open the hole to take a larger jewel there wouldn't be the material to hold it (and it would be too big, period).

 

Older models of ETA sometimes had a bushing at this location; the bushing is hourglass shaped, with a lot more contact in the plate.

[ifibrin]

16 minutes ago, nickelsilver said:

Older models of ETA sometimes had a bushing at this location; the bushing is hourglass shaped, with a lot more contact in the plate.

Would you happen to have any photos of such a design? Thanks!

[nickelsilver]

6 minutes ago, ifibrin said:

Would you happen to have any photos of such a design? Thanks!

Like this

 

[clockboy]

Here is ETA 2671 and looking at the drawing it does indeed have a jewel close to the edge of the plate but not like we are seeing in the original pic. The jewel setting hole looks damaged. 

 

https://www.cousinsuk.com/PDF/categories/27_ETA2660,2671,2678.pdf

[Marc]

47 minutes ago, clockboy said:

The jewel setting hole looks damaged

Here's another ETA 2671, or in this case a Cartier 077. The same 3 points of contact setting.

This was in a ladies Cartier Santos.

[clockboy]

What a poor design indeed. The picture displayed at the beginning of this post clearly shows damage to its setting so it might not be a straight forward repair if the jewel needs changing. 

[ifibrin]

34 minutes ago, clockboy said:

What a poor design indeed. The picture displayed at the beginning of this post clearly shows damage to its setting so it might not be a straight forward repair if the jewel needs changing. 

There is no damage to the jewel setting, although there is some discolouration around the jewel setting in the photo, which makes it look odd. In real life it looks exactly the same as the much better picture shown by @Marc, and the jewel is held securely by being “pinched” at 3 positions.
 

Still, I agree with you that replacing a jewel in this sort of U-shaped setting will be hard since a stump of a jeweling tool wouldn’t support the main plate on the part where the jewel is sticking out. Which is why I made this post to find out more.

 

Maybe you will need some way to support the whole main plate on the base of a jeweling tool, in order to replace jewels in U-shaped settings?

 

Edited November 9, 2021 by ifibrin

[nickelsilver]

As luck would have it I got into an ETA 2512 after lunch, and the hourglass bushing was worn as usual. I don't know if the bushings are available, but I make a batch here and there.

 

I keep a little more material at the edge, you can see the original isn't far from wearing through!

 

 

[ifibrin]

7 hours ago, nickelsilver said:

As luck would have it I got into an ETA 2512 after lunch, and the hourglass bushing was worn as usual. I don't know if the bushings are available, but I make a batch here and there.

 

I keep a little more material at the edge, you can see the original isn't far from wearing through!

 

 

Do you put a jewel in the bushing, or is the pivot of the third wheel directly inside the brass bushing? What is the purpose of the other hole in the ”8”-shaped bushing?

[nickelsilver]

9 hours ago, ifibrin said:

Do you put a jewel in the bushing, or is the pivot of the third wheel directly inside the brass bushing? What is the purpose of the other hole in the ”8”-shaped bushing?

There's not room for any commercially available jewel, it's just the pivot in brass like the original. I will probably make future ones from beryllium copper as it wears much better, now that I think of it (and I have some sheet the right thickness).

[Plato]

9 hours ago, nickelsilver said:

There's not room for any commercially available jewel

What size would you need, if it was available? 

[nickelsilver]

11 hours ago, Plato said:

What size would you need, if it was available? 

The round part where the pivot hole is is 0.80, but also has part of that circle removed, so it would have to be something like 0.40 diameter jewel, with a 0.12 hole. The smallest jewels you encounter normally are 0.70 diameter, and occasionally a 0.60 crops up. Outside of that it's really custom stuff.

[ifibrin]

12 minutes ago, nickelsilver said:

The round part where the pivot hole is is 0.80, but also has part of that circle removed, so it would have to be something like 0.40 diameter jewel, with a 0.12 hole. The smallest jewels you encounter normally are 0.70 diameter, and occasionally a 0.60 crops up. Outside of that it's really custom stuff.

That’s a real eye opener! Is it even possible to turn a larger jewel with the correct size pivot down to a smaller diameter on a lathe?

On another note, all these issues seem to explain why many watchmakers really dislike working on ladies movements.

[nickelsilver]

4 minutes ago, ifibrin said:

That’s a real eye opener! Is it even possible to turn a larger jewel with the correct size pivot down to a smaller diameter on a lathe?

On another note, all these issues seem to explain why many watchmakers really dislike working on ladies movements.

You can reduce jewel diameters, to do it well is a tricky process. One issue is the oil sink, which you would probably run into, rendering the jewel much thinner then originally and almost too fragile to be friction fitted.

 

I don't mind working on small movements, but they do eat more nerves.

[jdm]

11 hours ago, nickelsilver said:

You can reduce jewel diameters, to do it well is a tricky process.

We have a member that was able to adapt jewels with an improvixed lathe

 

[nickelsilver]

30 minutes ago, jdm said:

We have a member that was able to adapt jewels with an improvixed lathe

 

Yes, he did quite a nice job adapting a friction jewel for rubbing in. When actually reducing the diameter, and keeping it concentric, it gets harder (and I think one can see how much work it was just putting a proper chamfer on in the above video). I know, some people chuck the jewel similarly with shellac and use a diamond file on the perimeter, but this doesn't necessarily maintain concentricity. You really have to have a live spindle on the cross slide with a diamond grinding wheel to be sure.