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Sunday, March 29, 2015

Replacing a Balance Staff


This post is the 400th post on my blog since I started it three years ago.  That's a milestone worth celebrating  and I've known it was coming for quite a while but I wasn't sure how to recognize it.

Should I do an "about me" post?  Should I try to find an exceptionally unique model?  Should I do a "bloopers" post about all the watches I've screwed up?

Well, I finally decided that maybe I should do something more dramatic and tackle something most people have never seen.  I decided I would do a post on changing a balance staff.

The balance assembly is the most complicated element of a watch.  It's the heart that controls the timing of the watch regardless of temperature, position or mainspring tension.  There's a LOT going on in the elements that make up a balance assembly and it's usually the part that breaks when you accidentally drop a watch or mishandle it while looking at the movement.

I couldn't begin to count the number of broken balances I've got laying around.  Well, I guess I could count them but I'd have to separate them into broken balance pivots, messed up hairsprings, and missing impulse jewels.   My typical solution for a balance-related issue is to find another balance and that means get another parts watch and hope for the best.

However, fixing balance-related issues is par for the course when it comes to being a watchmaker.  Any watchmaker worth his salt can replace a balance staff.  He may not like to do it but he probably has had to do it more than a few times.

It's not hard to do if you have the right tools, know what to do, and don't mind practicing over and over until you get it right.

Let me show you what's involved.

I recently purchased a WWII military watch.  I got it mainly because it had a nice Star watch case and I needed it to restore a US Navy watch that used the same case.  So I swapped bezels but otherwise still have a very nice looking US Army model.  The yellow showing through on the case is brass from underneath the chrome plating.  It could be re-plated to look like new but I sort of like these watches to look rugged like they've been someplace few others would have the courage to go.

Inside the back cover is a dust cover (removed) and a 17 jewel 987A inside a movement ring.  The serial number on this movement dates it to 1944 - just as you might expect for a WWII watch.

Gently touching the balance wheel, it's clear to see that it wobbles.  It should spin smoothly but this balance wobbles considerably.  That means either one of the pivots (or both) are broken or one of the jewels is severely cracked.  I'll have to take it apart to be sure... it could be "all of the above".  You never know until you take it apart.

The upper balance staff pivot appears to be there.  It might be a little bent, it's hard to tell as they are so small.

After removing the balance from the balance cock I can clearly see there is no pivot on the hairspring side of the balance.  The balance rides on each of these pivots and if either of them is broken or bent, the watch will not run.  If a watch runs dial up, or dial down, but not both, then you know it's a balance staff issue.

There are a number of tools needed to work on a balance wheel and one of the most important is a quality staking set.  This type of tool has a goose-necked stand with a table that allows you to do all sorts of precise operations.  The long rods with special tips are punches (or stakes) and the little parts in the front rows are stumps that go into the table and give you a special work surface when needed.

This balance is worth re-staffing because the hairspring appears to be in good shape.  It will be the first thing I have to take off.  To do so I will slip my largest oiler into the slot of the brass collet in the center and then gently wiggle the collet until the collet and spring slip off the balance staff.

You have to be super-careful with hairsprings and not bend or change their shape.  They can be reshaped if you know what to do - but I'll save that for my 800th post.

With the hairspring removed you can see the balance staff is clearly missing a pivot.  The staff is held in place inside the balance arm with a tiny rivet of material.  You'll see more about that later.  At this point I need to remove the roller table from the other side of the wheel.

There are several different tools for getting a roller table off but I personally prefer this style.  It's designed to be used in a staking set.

Close observation of the roller table in my balance revealed that the impulse jewel is missing.  So I need to replace the impulse table with another one that has an impulse jewel installed.  You can see the little black D-shaped hole where it should be installed.  It's held in place with shellac and they can fall out if the shellac fails or if someone cleans the watch with alcohol (a typical newbie mistake).

Before I remove the roller table, I'll mark the wheel with a scratch to show where the impulse jewel should be pointing when I reinstall it.  That's important to keep the wheel "poised".  You'll learn more about that below.

In this shot you can see how the roller table remover works and why I had to remove the hairspring first.  The tool supports the back of the table.  I can use a punch to push the staff down.  When I do that, the balance will drop but the roller table and safety roller above it will stay on top of the tool.

Here the punch is lined up with the balance staff.  A couple of gentle taps with a hammer will free the table from the staff.

Success.  The balance wheel now has just an empty staff.  I'll do the same to another balance with a broken staff so I can reuse it's roller table and impulse jewel.

Here's a shot of the balance and the empty space where the roller table used to be.

One of the roller tables below has a red ruby impulse jewel.  The other has an empty hole.  The two smaller discs with a notch are the safety rollers.  These are installed with the notch pointing toward the impulse jewel and prevent the pallet fork from moving past the balance unless the impulse jewel moves it.  That keeps the balance from "over banking", or getting stuck on the wrong side of the pallet fork.

Now I can get ready to remove the broken balance staff.  First I find the smallest hole in the table that will accommodate the hub of the staff and allow the wheel to lay flat.

Next, I'll install a special balance staff removal tool in my staking anvil that will allow me to drive a punch straight down and push the staff out of the wheel.

There... now all I have is an empty balance wheel.  Some watchmakers prefer to use a lathe to remove the balance staff from the wheel.  That way you don't risk damaging the wheel.  I'd use a lathe too - if I had the $5000 it would take to buy one.

Here's a shot of the wheel and old balance staff.  I can still use the balance staff though - as it will help me select the proper sized punches for the next few operations.

I need a round-nosed punch with a hole just large enough to accommodate the hairspring side of the staff.  I'll also need a similarly sized flat-nosed punch.


And I need a flat-nosed punch for the other side of the staff.  It is lightly larger so it needs a larger hole.

Now I need a balance staff and I need the correct one for a 987A movement.  There are other 6/0 sized Hamiltons like the 986 and 986A and they use a different staff.

Here you can see the two pivots needed to properly support a balance wheel.  From here on out I need to make extra sure that I don't break or bend them or I'll have to start all over again.

First order of business is to put the roller-side of the staff into the flat-nosed punch that is inverted through the table of my staking set - so it's point upwards.  Then I can put the balance wheel onto the staff, making sure to orient it correctly too.  Then I put the round-nosed punch through the goose-neck of the staking tool, place it over the staff so it pinches the balance wheel between the two punches.  I give it a few strong whacks with the hammer to shape a new rivet on the wheel.  I'll follow the rounded punch with the flat punch to flatten the rivet and lock the wheel onto the staff.

There, a new staff is now installed inside the wheel and I still have two pivots.

Now I have to put the roller table back on and orient the impulse jewel with the mark I scratched into the wheel.  I use the flat punch from the riveting step as the new base in the staking set.  I'll use a special roller table punch with a notch for the impulse jewel to seat the table up against the flange on the staff.

Once the roller table is seated I can install the safety roller.  I'll need to make sure I put the cutout in alignment with the impulse jewel.

At this point I can check the poise of the balance with a special poising table.  The two pivots of the staff will rest on the blades of the table and create friction-free support for the balance.  It should rest in any position and not rotate to a "heavy side down".

Here you can see the balance on top of the poising tool.  It seemed to want to stop with the impulse jewel down... so I reset the table with the impulse jewel flipped 180 degrees.  That seemed to be better.  Poising a balance is very precise and tricky work.  I'm not that good at it and this wheel appeared to be "good enough".

Now I install the balance in the freshly cleaned movement without a pallet fork or hairspring.  In this setup the wheel should spin freely and spin for quite a while if everything is lined up well.

I will also check the balance in my truing calipers.  This tool makes sure the wheel is trued in the flat and the round.  Everything looked good and I was glad, as this is a good time to break a balance pivot if you're not careful.

Now I have to reinstall the hairspring.  I'll take a best-guess at the location of the stud relative to the impulse jewel.  It's important to try to get the balance "in beat" meaning having the impulse jewel line up perfectly with the center of the pallet fork.  A pair of punches support the balance while the collet is pushed onto the staff.

It's very hard to see the impulse jewel in the photo below but this is the angle I look at when I check the beat of the balance.  I should see the impulse jewel between the balance staff and the pallet fork jewel.

Now that the balance looks to be in beat.  I will reassemble the movement with a fresh white alloy mainspring and lubrication in all of the proper places.  With the watch wound up a little, it's the moment of truth.  Time to see if the watch will run.

Success - the balance is moving with vigorous motion.  Now it's off to the timer.

Well?  Hmmm.  This sort of pattern on the timer tells me the hairspring is hitting something.  The position of the spring is very important and it can bump into the center wheel while it oscillates and make extra noise.

There.... that's much better.  I cleaned the hairspring and demagnetized the watch.  After a little tweaking everything is now running just fine.  The beat error is a little high at 2.8ms but that's still in the acceptable range for me, especially since I've made it this far.  Why risk goofing up the balance by taking it apart again?

The dial and hands go back on and everything goes back into the case.  A fresh khaki canvas strap completes the restoration.  The strap matches the lume on the dial and hands perfectly.

How's that for a post to celebrate the 400th addition to my blog?  I may have made it look easy but it actually took me almost three hours from start to finish.  I have to admit that I'm a little proud of myself.  This could very easily have been an addition to a "bloopers" thread.


  1. Congratulations on your 400th post! I truly enjoy reading them.

  2. Yes, congratulations. You have an amazing hobby, and I get genuine pleasure from seeing your work.

  3. Thanks so much for this post, Dan, and congrats on your milestone! I have seen staking sets but could never really understand their operation until now. Question for you: I have seen comments about hairsprings being true "in the flat and round" before. Can you explain that for me? Does it just mean that when held horizontally or vertically the hairspring stays properly coiled and centered?

    Thanks! (Retroworx)

    P.S. If I fail to thank you for a response it is because I don't receive response notifications. Apologies in advance. ;)

    1. You can do a LOT with a staking set if you have the proper stakes and stumps.

      Hairsprings are very tricky beasts. They are a specially-shaped coil that starts in the center with the inner-most coil pinned into the brass collet and the coil should splay out evenly in a concentric spiral all the way to the other end.

      The length of the hairspring determines the rate the balance will oscillate (based on the mass of the balance itself). The other end of the spring is secured to the balance cock with the hairspring stud. How that final bend of the spring is shaped is very important. The American-made Hamiltons have a Breguet over-coil bend where the final coil bends up and over the body of the spring and ends at the spot where the stud will connect to the balance cock.

      Once the spring is secured in the balance cock, the hairspring coil should be perfectly flat (true in the flat) and perfectly centered (true in the round). The two prongs of the regulator fork should gently hold the last coil of the hairspring. Plus the impulse jewel should be in alignment with the pallet fork so the watch is in beat.

      If any of those things is not true, then the hairspring will need to be adjusted or the watch will not keep proper time. Reshaping a hairspring takes excellent vision, very fine tweezers and a healthy portion of real talent.

    2. Very generous with your time, as always. Thanks very much!

  4. Wonderful post Dan. Like many others, I truly get enjoyment out of watching you perform these truly amazing restorations. Congrats on the 400th and I look forward to the 401st and beyond !!