The watch was in generally good condition, but after testing, it performed very poorly in certain positions.
After close inspection at 80x on the measuring microscope, I realized that the balance bridge jewel was craked.
The balance wheel pivots were then burnished, as this surely cut into the profile of the balance wheel pivot.
This was done on the Jacot tool, with a steel burnisher. This reshapes the pivot to be smooth and hard.
The jewel was removed with a jeweling tool, but to replace it, a special tool needed to be manufactured.
Here I slice the teeth with a .25mm thick slitting saw.
This then is hardened. Had to use the same thickness as the slitting saw so that the teeth would not get deformed or open too much.
Further view.
The tool was then used to close in the steel around the new jewel set in the hole. These are called rubbed in jewels and were popular up until the 1940s.
The replaced jewel immediately improved the watch's performance in all positions.
Another problem found during testing was that the watch would periodically stop. The Geneva stop was at the root of the problem.
With the measuring microscope, the distances were measured to determine the correct size of the drive wheel and it's pin.
Once determined, the outer diameter is turned on a watchmaker's lathe.
Then the center hole and two other holes are drilled to form the sides of the tongue or driving pin.
This is what it looks like from the jig borer's miscroscope.
Then the holding pin groove has to be milled. The saw has to be centered along the center hole of the drive wheel.
Here the groove is done with a slitting saw.
A view of the slot.
This is then cut off. I use a saw instead of a parting blade on the lathe, so that the driving lip is not ruined.
Previous to sawing.
The piece sawed off. It has been purposefully sawed off thicker, in order to not ruin the drive pin.
To bring it down to size, i use a lapping holder (normally for polishing screw heads) to grind it down to size. It is cemented with glue.
Here I am preparing a reamer to create the square hole.
This is hardened and tempered.
The hole is reamed on the staking tool.
This was the first test out of a total of three required attempts before getting a satisfactory result.
Testing the final trail on the watch for the correct play.
Tempered and hardened.
Here showing two out of the three attempts.
Another view of attempted pieces, with lower bottom being the one used.
Placed and tested for various days on the watch (further adjustments were carried out).
