Pigs ears, shims, or pivot shortening...

[94marconi]

Been working on the Waltham 1892 balance staff project. Many problems have reared their ugly heads. This, while frustrating, is a good thing from the perspective that one learns from solving problems rather than have things go flawlessly. My current dilemma is one of balance staff end shake and the best way to correct it. The balance staff I purchased many yeas ago did not work out, but that is for the write up forth coming. The new balance staff has one thing in common with the old in that it is slightly bound when installed (1703A staff 6mm length) The previous repairer installed pigs ears on the balance cock to give some end shake. While a common thing to do and a simple fix, I did not like it and I filed them off. Research here and else where suggests a shim would be more acceptable. Would not shortening the pivot length be a better choice? Where time is money the shim seems the logical choice...or would anyone bother to go to the trouble of sanding and polishing the pivots for length where time is not an issue.  As always, thoughts and ruminations welcome. 

Ron

[szbalogh]

I would say try with shims first. Then You will see how longer the pivots are. If just a small bit longer they are the grind and polish.

But if the staff is much longer then check if the pivots wont be to short if grinded to size. And if one need to grind from the mainplate side pivot then the safety roller hight shold be watched.

https://youtu.be/9RuVJzr0Qtk?t=231

 

[94marconi]

Thanks szbalogh. Trying shims to assess the results makes sense. Good point on the safety roller height.  The staff as is is very barely binding. I will hunt around today to locate some shim stock. I have a feeler gauge set that goes down to 1.5 thou. 

Ron

 

[StuartBaker104]

Aluminium kitchen foil?

[94marconi]

Good thinking will have a go when I get home. A set of cheap automotive feeler gauges was one option. No big deal to cut up for shims. Should I be using Bergeon tin foil? lol

Ron

[JohnR725]

One of the problems with American pocket watches is variation of parts. It depends upon the particular watch but there were usually made in batches. If you watch the videos from the Various American factories you can see a lot of hand fitting of the components. It depends upon when they were made etc. But it does mean there is variation which means you may have to fit things like balance staffs.For instance for your watch there are two separate balance staffs. The 1703 5.70 mm in length and 1703 a 6.0 mm in length. Then 1703a came with three different pivot diameters where the 1703 came into different pivot diameters. So one model number watch variation in staffs. So more than likely originally the staffs may have been made long so the watchmaker could shortened to fit.

Depending upon how much shimming small strip of watchmakers tissue along one edge works fine. Usually don't need a lot of shimming occasionally piece of paper but if you go much beyond that you really should shorten the length of the pivots. Then if you have very much shortening it's best to do both ends.

 

[94marconi]

Thanks for the information johnR725. I was aware of the early and late production staffs my research indicated the early 5.69mm 1703 staff and the later 1703A staff at 6mm. I was not aware of the pivot size variation although I did see some references to a 12 pivot as well as my 11 pivots. It looks like the concensus is to go the shim route. The binding is so slight that not much of a shim will be required. The pigs ears are probably enough to do the job, it's just that it seems a bit low brow of a fix. 

Thanks again everyone for the advice. ☺

Hopefully will get a chance to try the shim idea tomorrow.  Now where to find that Bergeon shim material...

Ron

 

[94marconi]

Ok, had a chance to play with the shim idea. The kitchen foil measured out at .0005 in. and placed in board of the cock screw took four layers to achieve a free balance. By a free balance I mean that the balance would spin for 20 or so seconds with several puffs of air from the blower dial up and dial down. So it looks like  a two thou. shim will achieve a free balance with no perceptible end shake. How much end shake should there be? In my mind with zero or next to zero end shake there would be a problem when the jewels are oiled. Research has not provided a rule of thumb so to speak...

Ron

[94marconi]

Well upon further experimentation I now have the shim down to .04mm or 1.5 thou.and have end shake. I can see and hear the balance staff play when I shake it side to side and move it up and down. I now have the balance spinning free for a minute dial up and dial down. Not sure why the shim size changed...redid the shims several times and it seems to be constant. How much end shake is a guess as i have no way of measuring beyond an educated guess.

Ron

[szbalogh]

6 minutes ago, 94marconi said:

 How much end shake should there be?

If You place the thumb on the balance cock over the balance and push just really slightly then the balance should not stop spinning. On the other hand one should not hear loud gongs if tilting from one side to another. 

I would measure 10 or 20 layers of foil then devide by number to get more accurate thickness.

[94marconi]

Good point on averaging the foil thickness. I will cut off a piece of the feeler gauge as that measures accurately. Will then repeat the tests. Things look pretty good so far. The balance wheel is pretty bent up and very out of balance. That will be dealt with after the replacement staff is installed and the end shake rechecked.

Ron

[JohnR725]

So shimming is fine but remember there's more to it then getting end shake. Everything has to be in the correct place. Then there are published numbers but you're dealing with an ancient pocket watch so the numbers kinda fly out the window. In the case of Rolex typically they want a balance end shake of .020- .030mm. If you're in a obsessed student in school the first link comments about .01mm which is way too little end shake. But I'm giving you the link because it talks about what you need to be looking at things from the side view. Second link is similar to the first. Go to page 315 the escapement. So here you get a little different end shake numbers and comments about what you should be looking for.

So I would continue with shimming just so we can see what happens. But just remember you might end up with the balance wheel not exactly where it's supposed to be because the pivots are too long for this particular watch. Then shortening them would be preferred option. If it's a very tiny amount you can do one end but if it's a lot then do both ends.

http://raulhorology.com/2012/10/setting-up-the-escapement-eta-6498-end-shakes-divisions/

http://www.mybulova.com/sites/default/files/file/Joseph Bulova School of Watch Making - Repair.pdf

[94marconi]

Very informative indeed JohnR725. It is all to easy to develop tunnel vision when focusing on a single problem and lose sight of the rest of the component interaction. This I should know as a mechanic. The balance staff and balance assembly was the starting point of the project and of course getting that right was my main focus. But I see that a little foresight would serve me well going forward...That being said, it looks like the shimming experiment is a success for now at least, until the new staff is installed.I think I will continue with the truing and poising of the balance with the current staff just in case there are any issues practice wise... Thanks again for all the insight JohnR725 and szbalogh 

Ron

[rodabod]

I'm working on a Jaeger LeCoultre Cal 450 just now that looks like this under the balance cock:

https://s32.postimg.org/ax5vxlv51/image.jpg

https://s32.postimg.org/ief3ctko5/image.jpg

https://s32.postimg.org/e6owht8md/image.jpg

https://s32.postimg.org/k8wj8ax2d/image.jpg

The staff is broken, so I've borrowed a Cal 449 (sub seconds version of 450) from a good movement. 

With the good balance in the 450, there is serious end-shake. Should I attempt to flatten the punch marks (pigs ears)? I'm not sure by looking at them how much extra end-shake they would cause. 

And how do I remove them? With an Arkansas stone maybe?

Thanks. 

Edited February 23, 2017 by rodabod

[94marconi]

Luckily mine were on the balance cock and not the main plate. I used a fine flat file and had no issues at all. My mating surfaces were not finished so a light touch up with some sandpaper to remove the file marks was all that was needed.

Ron

[rodabod]

Thanks Ron.