Basic watchmaking tips - replacing a balance staff

It’s not a split balance.

So the first adjustment I made was just to slow the watch down, and that was installing two timing washers directly opposite each other. On a split balance you would do this on the screws that are right on the balance arms - those are the timing screws as shown here as "2":



Image from Wiki

The others if you change those, you change the temperature compensation of the balance, so poising a balance like this gets tricky, as you don't want to change it too much for basic poising, as that will make a change to temperature compensation as well. This is why this type of balance was abandoned once more stable materials were found.

So in my first post I mentioned that there are staffs that are not riveted, but fit into the balance by friction. I posted an image of the arrangement used by Waltham, but they were not the only makers to use this method of fitting staffs. To the best of my knowledge, this style of fitting staffs was used by US companies, and not really by others. I don't ever recall seeing or hearing of a Swiss company that used friction fits staffs for example - maybe there are but again it has never come to my attention.

I don't really work much on US pocket watches, so I don't often do this kind of staffing, however a watch with a Hamilton movement did come in for service and the staff was less than perfect:



Closer look:



The other side was worse:



So the job starts out like any other staff replacement - I remove the balance spring and roller table, after marking their positions:



So looking at the balance, you can see that there is a blued steel hub, and the staff goes through this hub:



The hub stays in the balance, and the staff is removed from the hub. I get out the staking set, and select the stumps and punches carefully so that the staff will go through, and the hub is fully supported:



I then used a punch to press on the staff, but not on the pivot:



Small taps with the hammer (very small) are enough to drive this out:



I'ce not fully removed it so you can see more detail of how the staff and hob go together:



So I'll carry on in the next post with the installation...

So here is the new staff, original Hamilton staff:



Nice of Hamilton to make the staff the same for all these grades of 10 seized movement:



So the balance is back on the staking set, flipped over from the last series of photos, and I've started the staff in the hub - note that it goes in quite a ways before tightening up:



I now use a punch to come down and press on the small shoulder on the staff:



And then press it in place - again very light taps using the watchmakers hammer:



Now I am already set-up to install the roller table back on:



Once that is installed, I flip the balance over to install the balance spring assembly. However the collet on this one is quite loose, so I use a collet closing tool to gently squeeze the collet tighter, keeping fingers crossed that the collet doesn't crack!



Now the collet fits snugly on the staff, so it's pressed in place:



The staff has now been changed:



And here it is in the 921 that dates to 1948, so this is 74 years young...



Cheers, Al

Wanted to post another follow-up here. In my initial procedures, I mention a test that ensures that the staff is firmly riveted in place:



So here's is an illustration of why this is important. I was working on a watch recently that came in not running, and the first thing I do when assembling the watch is to oil the balance jewels, and do some checking of the flatness and concentricity of the balance spring, so it's only the balance mounted on the main plate:



Normally you can make a balance oscillate using a blower, or just by flicking the movement holder, but when I did that here, the balance almost stayed stationary. I though this might be a case where the collet for the balance was loose, so I took the balance out and found this:


The balance staff was loose, so although the roller and balance spring were tight on the staff, the wheel was free to rotate. This meant that when the pallet fork would impart the impulse to the roller, instead of turning the entire wheel, it would just turn the staff.

I ended up replacing the staff in this, as I wanted to make sure that it was properly riveted, and would not potentially come loose again. So whoever performed th last staff replacement on this watch, didn't ensure that the staff was riveted firmly enough.

Cheers, Al