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ETA 2390 shims and dimples


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Just wanted to show something odd that I ran across, and see if anyone might have an idea of why someone would do this. When I opened up this watch, I found that a previous repairer had shimmed the train bridge with paper at the OD.

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After further disassembly, I saw that there were also dimples on the other side of the bridge, I'm presuming they were put there to increase end shake. At this point, though, they are worn down enough that they can't be doing very much.  

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So a bit puzzled, I proceeded to clean and re-assemble the movement, without the shims or renewing the dimples. The train bridge was a bit tricky to get in place, being more of a cock than a bridge, but once I had everything lined up and tightened down the wheels all moved freely, and as best I could tell end shake was good.

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So, the question is, what was all that hacking of the bridge about? An attempt to make it easier to get the bridge lined up? Inquiring minds want to know!

   

Edited by dadistic
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Depending on where the shim is, it could be either to reduce or increase end-shake.

If the shim is outboard of the screw, it will tilt the balance cock inwards and thereby reducing the effective distances between jewels.

If the shim is inboard of the screw, The tilt will be upwards = increasing distance between jewels.

This way is not ideal as the jewel holes will not be inline and the pivot will sit an an angle.

One possible scenario is if the pivot had mushroomed. It would be possible to remove the trace of the 'mushrooming' but this will leave the pivot slightly short. Shimming may be a way to reduce the resulting endshake. Any hack is to reverse the cap jewels as this gives a very slight reduction to the endshake.

Anilv

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maybe the previous watch-smith considered it wasn't enough axial shake.

So that begs the question: how do you know you have enough axial shake?

Good question!  A difficult thing to measure, I'm doing it by eye and feel. Should be a noticeable amount, enough to prevent the pivots from binding. Too much would be when wheels and pinions move enough that they are not fully engaged. This one looks good to me, and the train is as free as most other watches I've worked on, although I admit my experience is limited. 

The real test will be to get it on the timegrapher, and see how it's running. Right now the movements running on the bench, as soon as I have some time I'll check it out and we'll see.

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Worked a little bit more on this movement, and so far I don't see a problem that I'd for sure blame on the train bridge. Some other things to address first, I think.

Here's how it's running, dial up -

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Not horrible, but not great. Amplitude a bit low, I think I'd like to see consistently > 270, and the beat error is a bit high.

Crown down -

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Ugh. Big drop in amplitude, increase in beat error, but still keeping relatively good time.

Crown up -

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Whoopsie! That's not good. My limited knowledge suggests that this is some kind of balance issue, I think most likely hairspring, but I suppose poise could do this too, but I don't know why it would be out of poise. Next, off comes the balance, maybe I can see what the problem is there.

Any suggestions on what to look for?

Edited by dadistic
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17 hours ago, dadistic said:

Any suggestions on what to look for?

Issues with poise (if it is indeed poise which is causing positional variation) will be more obvious at lower amplitudes. So, my first question is, are you sure that the upper and lower balance jewels are absolutely clean? Did you peg them out, and has the balance been in the cleaner too, to remove any residue from the staff?

Your hairspring looks ok from what can be seen in the photos, but you must inspect it while running to make sure that no coils touch and that none are fouled by any other parts. Use lots of light and a strong magnification loupe. Also check that the indexing pins on the regulator arm are barely hugging the hairspring.

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The only thing I didn't do was peg the incabloc hole jewels, I'd have to think about how to hold the chatons to do that. maybe a pin vice? Everything else was cleaned in One Dip, but this movement was pretty grotty so a second round may be in order. I'm thinking I'll pull everything off so I can examine just the escapement after a second round of cleaning. The stud carrier is fixed on this one, so being able to see will certainly help if I attempt to adjust the roller jewel position.

Thanks!

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I'm not convinced that adjusting the roller position is a good idea for adjusting beat error as it will put the balance out of poise. I would try it the normal way by moving the hairspring collet very, very slightly.

Give the jewels and the caps a good clean. The caps should have had an almost mirror finish before placing the oil on. Use pegwood/cocktail stick/stiff brush to clean out the upper and lower jewels after they have soaked. I usually soak the pegwood in the same solution to help it along.

Edited by rodabod
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Oh, I meant adjusting the roller relative to the pallet by moving the hairspring collet, not the roller table :) When I'm inspecting cap jewels and pallet jewels, I angle them around until I catch the light and can see the "shine" off the surface. If I see crud still on the cap jewels, I'll rub them on watch paper until they are clean and clear. Using soaked pegwood on the upper and lower jewels sounds like a plan! 

Thanks again!

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3 minutes ago, vinn3 said:

I  think, shimming is not honest repair, but its common.  vinn

I can accept shimming; some Russian movements were skimmed ex factory.  On the other hand, the idea of dimpling a machined surface make my cringe! 

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  • 4 weeks later...

I finally had a chance to get back to this watch, and I decided to peg the balance hole jewels and see if that helped. So, I worked out a way to hold the hole jewels with a bit of rodico and got some nice sharp pegwood in the holes. Here's how it's running now.

Dial up -

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Big difference! There must have been crud in those holes,  amplitude is up quite a bit.

Crown down -

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Drat. Still a big drop in amplitude. 

Crown up-

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Oh well. Amplitude is better in all of the positions, but the drop from dial up to the crown up/down positions is just as drastic. Worth making a note about pegging the hole jewels, though. I'm not going to skip that again. 

While I had the balance jewels off, I took a look at the pivots with a 10X loupe. It looked to me like they were a bit mushroomed at the end, but I'm not sure. Balance is coming off again, I'm going to take a closer look at the pivots. Have to do that to correct the beat error on this one anyway.

 

 

 

 

Edited by dadistic
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Generally speaking amplitude in the horizontal positions (DU/DD) is noticably greater than in the vertical due to the reduced contact area between the domed end of the balance staff and the flat surface of the cap jewel (horizontal) compared to the contact area between the side of the pivot and the side of the hole jewel in the vertical positions. In fact one of the adjustments that can be made to improve (reduce) the delta (difference in rate between positions) is to very slightly flatten the ends of the balance staff pivots so as to redude the difference in contact area between positions at the expense of amplitude in the H positions, although this should only be considered if the sides of the pivots are in as good order as they can be.

A drop of 60 degrees from H to V is probably towards the higher end of what is reasonable to expect, but in my opinion it is not at all unacceptable in a vintage watch, especially when you're getting 300 in the H positions.

It may be worth checking your oiling. I have in the past found that over oiling the balance pivots increases the delta between V and H positions; an interesting experiment would be to remove all of the oil and put it on the timegrapher dry to see what values you get and then adapt your oiling technique to get the optimum balance between adequate lubrication and minimising viscous drag. I assume you are using 9010 or similar for the pivots, if you are using anything heavier then changing that would help.

Also you will probably find that sorting out the beat error will hellp to improve things

If this were my watch and I was happy with all of the above but wanted to try and improve things still further then my next move would be to polish the balance staff pivots to try and reduce friction in the V positions.

 

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Thanks! 

I think for the purposes of this thread that trying to reduce the the drop is worthwhile, and I like your idea about dry vs. oiled balance pivots. I'm fairly confident in my oiling, but I've never tried this so you've sparked my curiosity. I'm using 9010, and putting a drop on the cap jewel so that it covers ~ a third to a half of the jewel. One interesting thing I noticed with these cap jewels, they have a step on the pivot side, so that the center is raised with respect to the outer edge. I'm not sure if I can get a picture, but I might try because I haven't seen this before.

Since the watch is already apart again, my next step is going to be trying to get a good view of the pivots. Once I do that, I think this is the perfect opportunity to try out my Jacot tool, but since this is my first attempt, it might take me a while to get it together. 

Onward!

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5 hours ago, Marc said:

Generally speaking amplitude in the horizontal positions (DU/DD) is noticably greater than in the vertical due to the reduced contact area between the domed end of the balance staff and the flat surface of the cap jewel (horizontal) compared to the contact area between the side of the pivot and the side of the hole jewel in the vertical positions. In fact one of the adjustments that can be made to improve (reduce) the delta (difference in rate between positions) is to very slightly flatten the ends of the balance staff pivots so as to redude the difference in contact area between positions at the expense of amplitude in the H positions, although this should only be considered if the sides of the pivots are in as good order as they can be.

A drop of 60 degrees from H to V is probably towards the higher end of what is reasonable to expect, but in my opinion it is not at all unacceptable in a vintage watch, especially when you're getting 300 in the H positions.

It may be worth checking your oiling. I have in the past found that over oiling the balance pivots increases the delta between V and H positions; an interesting experiment would be to remove all of the oil and put it on the timegrapher dry to see what values you get and then adapt your oiling technique to get the optimum balance between adequate lubrication and minimising viscous drag. I assume you are using 9010 or similar for the pivots, if you are using anything heavier then changing that would help.

Also you will probably find that sorting out the beat error will hellp to improve things

If this were my watch and I was happy with all of the above but wanted to try and improve things still further then my next move would be to polish the balance staff pivots to try and reduce friction in the V positions.

 

Next time I encounter this issue as an experiment I will try different lubrication just to see what difference it makes.Ps excellent post

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This is a nice website which discusses the importance of clean pivots, jewels, and polish:

http://adjustingvintagewatches.com/cleaning-balance-pivots/

 

Did you put the balance in the cleaning machine to remove the crud from the staff itself? Sometimes it can be almost invisible, and there will be a light film of varnish-like substance which is dried oil.

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3 hours ago, rodabod said:

This is a nice website which discusses the importance of clean pivots, jewels, and polish:

http://adjustingvintagewatches.com/cleaning-balance-pivots/

 

Did you put the balance in the cleaning machine to remove the crud from the staff itself? Sometimes it can be almost invisible, and there will be a light film of varnish-like substance which is dried oil.

This is a great link and all forum members should read this and digest. The only issue that I have encountered is when thoroughly cleaning is not easy especially when the movement is a low grade vintage movement. With these movements even removing the hairspring is a challenge because it is not held with a screw but riveted and the jewels are rubbed in. With these movements I soak with a de-greaser, then wash in my cleaning machine then soak again afterwards and inspect with my microscope. I then lube with a auto oiler.

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Hi! I'm familiar with the adjustingvintagewatches website, but I should have a look again. The balance was cleaned in my ultrasonic cleaner, and again in one-dip. Pivots are shiny, but there could still be gunk. Dial up and dial down were about the same, about the variation I get when I restart my 1000 timegrapher.  I've also heard of people charging a piece of pegwood with diamond polish and poking and turning the pegwood  on the pivot. I have a jacot tool, though, so I think I'll try that once the balance is disassembled. Was hoping to do that yesterday, but I got sidetracked by a plumbing emergency :-) Maybe today.

Thanks! 

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  • 3 months later...
  • 6 months later...

So, not too long after my last post in this thread, I did make an attempt at taking pictures of the balance staff pivots. To me they looked a bit rough, but honestly it's hard to tell. I think I see scoring on the sides, that would certainly explain a large drop in amplitude between positions.

 

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So,  I decided that I would attempt to to take @Marc's advice, and polish the pivots. I went ahead and set up this baby, which I had not used before. I have an idea on what to do, but you never can tell how things are going to go until you actually try it!

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