Patek pocket watch repair – Part 2, making and replacing the balance staff, new stem fabrication
In Part 1 of this repair I had to make a new arbor for the escape wheel (see my earlier post if you haven't read it).
Unfortunately the bottom balance staff pivot was bent and when I tried to straighten it out with my Seitz pivot straightner it snapped. Obviously it was much harder than normal as the pivot straightner should have been able to do it's job.
So with no access to any spare staff, I had to make one.
Here is the old staff being pressed out of the balance after I cut away the rivet. Someone had previously replaced the staff as there was a slight bit of material removed around the balance arm hole.
With the staff removed I was able to take the dimensions and make a new one from round silver steel stock. Luckily the staff is quite large and measures just over 5.00mm long making it easy to work with. The pivots measure 0.10mm.
The new staff was riveted to the balance and the roller table installed before it was poised. Poising is checking and adjusting the balance wheel to make sure that it doesn't have any heavy spot. In other words “balancing” the balance wheel so that all the mass is centered on the pivots. Poising is mandatory and always required after a new staff is installed. If the poise is off and the balance is heavier on one side the vertical rate will not be accurate.
The original stem was in very poor condition and did not fit the hole in the mainplate, being somewhat too small which was causing all sorts of problems.
Here's the new stem I made
In this view you can see that the new stem fills completely the mainplate hole, no side play anymore