Sunday, 28 June 2015

Making a balance staff

Making a balance staff is one of the most demanding jobs in watch repair. This is because the balance pivots can be as small as 0.1 mm in diameter. Also, there are numerous clearances and tolerances to be taken care off. Over the years I have made and collected the tools required for this delicate operation. Last week I decided to take the plunge.

In the picture below you can see the balance with the balance spring and roller table removed. The old staff is on the balance and you can also see a balance staff blank. One can start with a blued steel rod but a blank saves a bit of time.


The old staff is removed. I did this on the turns because it is slower and offers more control. Care should be taken that the balance is not touched while cutting the rivet, nor should it be distorted during removal of the old staff.


Below you can see the blank mounted on the special runners I made for my turns. First, the seat for the balance is turned and then the arbor for the balance spring. The balance should be a perfect fit. Too tight and it will get distorted, too loose and it will be out of round. 


Here is the partially turned staff ready to be mounted on the balance. Mounting the staff at this stage eliminates the need of a dog.

And here is the staff riveted to the balance.

 Next, the arbor for the roller table is turned. Finally, the two pivots are turned. One can safely reduce these only to about 0.3-0.2 mm on the special runners. Beyond this the pivots are reduced on the Jacot tool. This is a special turns made specifically for reducing and rounding off fine pivots.


Below you can see the finished staff with the correct diameter and lengths of the two pivots. There is scope for improvement, particularly in the shape of the pivots and polishing. All the same, it feels nice to be able to make something so tiny and delicate.

The proof of the pudding is in the eating. So, here is the staff during a test assembly-
video

Kind regards

Aditya