Staffing a Balance

Well after ei8htohm's well thought out piece on poising a balance I decided to take some pictures the next time I had to staff a balance.  John's article is available here as  Poising a Balance .  Normally you need to poise a balance after you replace a balance staff - in John's case he purchased a vintage watch that was likely restaffed without poising and had large variations in timekeeping in different positions.  So interestingly enough between the two of us we've presented the material backwards.

The story behind this repair is the result of the gift a 14k gold Hamilton Gilbert I gave to a friend as a graduation present from law school.  He goes through a ridiculously sensitive metal detector every time he enters and leaves the courthouse and has to remove the watch to avoid setting it off.  Well as to be expected when you have to hurriedly take on and off your watch multiple times a day the likelihood of it slipping and hitting a the floor increase substantially.  The other day I got a rather upset phone call wondering if I would be able to repair a dropped watch.  The watch appears to have hit crown first as the keyless works needed to be straightened out and as is common in an non shock protected watch the pivot on the balance staff was history.

You'll have to forgive the low quality magnification - but the only way I could get close up pictures of a rather small balance was to use a 10x loop in front of my Sony FD-83.  There should be a tiny pivot on top of the shoulder of the balance.

The first step is to remove the hairspring.  Remember to mark the location of the hairspring stud.  (You can see my black magic marker right by the balance screw.)  I cheat and simply use a screwdriver and ROTATE (don't pry) the screwdriver under the hairspring collet.  Ei8thohm's article describes the more accepted and safe way to remove the hairspring so that is why I'm not bothering to show the process.  In both approaches the balance is supported on an anvil.  Also in my case and John's the arm's of the balance are able to lay flat on the anvil.  If this is not the case you must support the arms either through a cutout on the anvil or using a stump on a staking set.  A key point working on a balance is to remember never to unsupport the balance arms or deform it in any way.  (Ask me how I know this...)

Take a good look at the blurry (10x) balance. ( Note: the scratches were put on there by the last person that staffed this particular watch.)  Notice the ring called a rivet that is on the outside edge of the staff.  The rivet holds the staff to the balance and presents a large challenge to the staffing process.  We have remove this rivet and not deform the balance by either bending the arms or by making the hole that the staff passes through concentric.  There are two approaches to this, one with a staking set that I use, and the other is to put the balance in a lathe and cut the rivet off.  The lathe takes more skill, but once mastered many feel is safer.

Prior to using either technique to remove the rivet you have to remove the roller table from the other side of the balance.  There are also different varieties of roller table - some are one piece some are two or more pieces.  How you remove them depends upon the type.  Also note that not all balances center the impulse jewel in relation to the arms of the balance.  In this case I marked where the impulse jewel aligns on the rim of the balance.  Among the ways to remove the table  is a simple $10.00 tool, but I like to use my staking set.  Both the stump (lower piece) and the stake are specifically designed to not bend the balance and not break the pivot (in case the staff was in good shape and you just needed to remove the roller table).  The fingers of the stump support the roller table and the stake will push on the shoulder of the balance staff and push the staff out of the roller table.

The key is to use a small brass hammer and gently tap the stake while supporting it with your free hand so that it does not bounce (recoil) after you strike your blow.  There is a bit of an art to determining how hard or soft to hit a stake so by all means practice a few times with some old unwanted balances first.  After a single gentle tap the balance drops free and the table remains supported on the fingers. (Note the bottom pivot is intact.)

Now we are going to remove the rivet.  The picture below is FYI ONLY.  You never want to try to drive a staff out without supporting and holding the balance.  In this case if I hammered the stake the arms of the balance would curl up slightly and I would risk making a concentric hole in the balance by forcing the staff through.   It is also important that you select a hole in the table of your staking set that will allow the staff at its WIDEST!!!! part to fall completely through.  If you can't decided between two sizes on the table choose the larger hole.

Here is the same specialized stake with the appropriate support added.  This will help prevent the balance from becoming deformed and also support around the hole for the staff, but you will still stress the balance more than the approach with a lathe.  You will have to give several gentle taps with your hammer and you will feel the rivet be cut and the staff slide into the table.

If you did everything correctly your balance will be flat on the table and you will see the rivet that you just cut off.  To the right of the rivet is a picture of our replacement staff.

Now we are going to use a our staking set to assemble, rather  than disassemble the balance.  We need to select two stakes one round nose and one flat nose.  We are going to use the round nose first so as to gently fold the new rivet over the balance without breaking it off.  Again you want the stakes to be slightly loose and go all the way down the rivet allowing the rest of the staff to fit inside the stake.

Starting with the round punch we gently tap the rivet into place.  I rotate the balance 90 degrees, tap, rotate another 90 degrees, and repeat for a total of four times and 360 degrees.  Repeat the process again with the flat nose punch.  Make sure the rivet is secure and the staff does not rotate.

The next step is my favorite part.  You can check to make sure that everything is "plumb, level, and square" by replacing the balance in the watch without hairspring or roller table.  Give a GENTLE puff with your blower and set the balance spinning.  Examine the balance and make sure there is no wobble or any deformity.

Recall that I said you must support the balance to prevent bending the arms of the balance.  In this case to replace the roller table we need to use a stump in our staking set.  My particular staking set inverts and allows you to use a stake as a stump so pictured below is an inverted punch used as a stump.

Again we choose the appropriate flat nose stake to push the table back onto the staff.  Some roller tables may require you to use a punch with a cutout for the impulse jewel.  You need to align the impulse jewel by eye.  There is nothing that guides the roller table into any position..  After you are comfortable with the alignment give a couple of gentle taps and the roller table should be firmly attached.

It's time to invert the balance and replace the hairspring.  You don't have to use a staking set as John demonstrated, but since I have it out to do the staffing I'll use it.  Simply,  find the appropriate size hole in the table and a flat nose punch.  Align the hairspring stud with the mark on the balance and with your FINGER press the stake forcing the hairspring collet on the staff.

Now comes the fun...  Replace the balance in the watch and check the performance.  Between removing the hairspring and the roller table I can almost guarantee that the watch will not be in beat.  Remove the balance turn the collet and replace it back in the watch.  Determine that you guessed wrong and that the collet needed to be turned in the other direction.  Remove the balance rotate the collet in the other direction.  If you are lucky you guessed right and the watch is now in beat.  If not repeat again until you are happy.  After the watch is in beat you need to check the positional accuracy and determine if the balance needs to be poised.

After I posted this article I received several suggestions for getting the watch in beat.   John's suggestion was "to mention that the way I check for beat (at least in the midst of such massive and invasive surgery), is to place the assembled balance in the movement without the pallets and observe whether or not the roller jewel lines up with the pallet pivot. That will at least give you a rough starting place and in my experience is good enough (as perfect beat doesn't always seem to mean better performance anyway)."

Another excellent suggestion I received by e-mail was "On fitting the staffed balance back into the movement, let down the mainspring if this has not already been done, and by inspecting how the pallet lies between the banking pins one can usually see in which direction
the collet needs to be turned if not in beat."

Good luck and happy staffing!