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First balance staff replacement!

LittleWatchShop
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LittleWatchShop Distinguished Member

LittleWatchShop

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Oh boy this was hard. 

So I had an A-17 Waltham 6/0 military watch with a busted staff.  The first one I ordered was incorrect.  The second one I ordered was correct.

I watched this WRT video about a dozen times: "Fitting a new balance staff to a vintage 1940s cyma www military watch"

I read the Bulova training manual (fitting a balance staff) that somebody posted the other day.

Once I was comfortable with the process, I dove in.

Imagine that, just like on the video, the roller came off in two pieces.

Removing and installing the staff went off pretty much like the video said.  I used a truing tool to make some slight tweaks until I figured any more fiddling would make it worse.  Then on to assembling the broken roller.

I had taken pictures of the balance in all positions, so I knew how it had to go back together.  Got it on, and examined under a microscope and was happy.

Then I put the hairspring on without any issues.

This is where it became incredibly hard.  The way the hairspring is shaped (pretty odd), it was nearly impossible to get the hairspring into the regulator pins while getting the stud in place.  At one point I thought I had it so I turned over the balance and cock to see how it hung.  Something jiggled and the hairspring looped over the stud screw.  Rather than take a chance of bending the hairspring, I removed the screw so that the hairspring would fall away.  So, with the undamaged hairspring away, I had the task of getting that damn set screw back into the cock.  With my dad's copious amount of tools, I found one that is like a locking tweezer with a round hole in the end.  I locked the screw in this and had plenty of control to put it back where it came from!

After much fiddling I finally got the hairspring installed with the stud in place and the hairspring properly installed in the regulator pins.

Then, I put the balance back into the watch and it started ticking!  Wow...what a great feeling.

This took me about 3 1/2 hours (starting with a disassembled balance that I had started over a week ago).

2021-03-22 22_39_21-Photos.png

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canthus Super WRT Addict

canthus

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Posted (edited)

Getting those screws in is a real pain.  My method is to use a very very small piece of rodico (or bluetac if no rodico), push the screwdriver through the rodico, engage the slot with the screwdriver and push the screw/driver back onto the rodico so the screw is held.  The screw can then be fitted easier and once engaged the rodico can be removed.  A dial dot also works but can leave adhesive on the screw which needs to be cleaned off.    Plastic magnetism !!

Edited by canthus
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LittleWatchShop Distinguished Member

LittleWatchShop

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Here is a picture of the hairspring showing how it takes an abrupt turn crossing over the coil and then to the stud which lies inside the circumference of the outer extent of the hairspring.

When I took the watch apart (weeks ago), I thought I had damaged the hairspring.  Nope.  This is the way it is designed.

Any thoughts on this configuration?  Seen before?  Reason?

2021-03-23 07_00_08-Photos.png

Edited by LittleWatchShop
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Tmuir Distinguished Member

Tmuir

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47 minutes ago, LittleWatchShop said:

Here is a picture of the hairspring showing how it takes an abrupt turn crossing over the coil and then to the stud which lies inside the circumference of the outer extent of the hairspring.

When I took the watch apart (weeks ago), I thought I had damaged the hairspring.  Nope.  This is the way it is designed.

Any thoughts on this configuration?  Seen before?  Reason?

 

That is a Breguet Hairspring, basically it is superior to one that just spirals out.

Have a read of these sites.

https://www.buzzufy.com/blog/2018/09/24/the-breguet-or-overcoil-hairspring/

 

https://www.breguet.com/en/history/inventions/breguet-balance-spring

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Nucejoe Distinguished Member

Nucejoe

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1 hour ago, LittleWatchShop said:

 Reason?

I guess the articles Tmuir provided link to does explain some resason, here is what I figure,

Some advantages; The diameter of overcoil gets increasingly smaller as you get closer the stud so hairspring  moves less between regulator pins during oscilation,  therefore isochronicaly enhanced  , almost as good as free sprung.

As you can see breguet hairspring allows longer length therefore bigger amplitude of oscilation.

Both effect directly increase percision of regulation.

Disadvantage,  tall balance staff.

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