Replacing a balance staff

Prompted by a record of repair watch I have with broken balance pivots, last week we learnt how to replace a balance staff. There's quite a lot to do, but it's certainly not has hard as I expected!

The first step is to remove the delicate hairspring to access the whole staff. This can be done by using screwdrivers as levers underneath the collet.

0.5 and 0.6mm screwdrivers - These parts are small!

Then, after removing the jewel roller, we need to remove the old staff from the balance. To preserve the shape of the old balance staff (essential if you need to make the new one!) we use the staking set to punch it out of the wheel.

Andrew using the staking set

Next is to fit a new staff and rivet it on, using the staking tool again. balance staffs have an undercut which makes this a relatively easy thing to do. Once it's on we use a poising tool to check the wheel is mounted straight, and won't wobble when it spins, which is very important.
Then we make sure the wheel and staff are balanced properly; if they aren't the isochronism of the escapement will be affected. We use a ruby-jawed vice to roll the wheel by the pivots. We use an air blower to start it moving, and if the wheel is perfectly balanced it won't roll backwards when it stops.

Making sure the jaws of the vice are perfectly flat

If it's not balanced we need to make the heavy part of the balance lighter. We do this by removing material from the heavy part of the balance. We do this underneath so it can't be seen when the watch is back together!

Using a cutting tool to remove material and make the balance lighter on this side.

Below you can see a video of a balanced wheel. you can see all the cut marks from where the wheel has been practiced on over the years!

Testing the balance!

 Once it's balanced, you replace the safety roller and double check it's still balanced. It's 'better' to put the jewel between spokes of the wheel so you can put the watch into beat easier. It also looks nicer!

Once more on the vice...

Lastly, you replace the hairspring, and put it back in the watch!

Supporting the wheel on a staking block to protect the new staff.

 Easy!