This vintage Rolex Oyster Perpetual was brought in recently and required extensive repair. It was well beyond the scope of a standard overhaul. This particular post will cover the aspect of re-bushing the barrel bridge and the rest of the overhaul will follow at a later date.
So what exactly is re-bushing? All train wheels (gears) in a watch are mounted on an arbor, or axle. Those axles usually have small pivots on the ends of them and those pivots are seated in the jewels of the train. That is why watches have jewels. The pivots of these wheels are made from steel, and the jewels are synthetic ruby. The barrel, which houses the mainspring, is similarly constructed with the arbor, or axle, being made from steel. Traditionally, however, the barrel arbor doesn’t sit between two jewels, but between a brass bushing. Modern watches, such as the Rolex 3135, use a jewel instead of a bushing.
Because the bushing is brass and the arbor is steel the seating can get worn away over time. Below you can see the wear on the underside of the bridge.
Unfortunately these are not friction fit and they are actually part of the bridge itself. Due to this fact, sloppy barrels are common practice among vintage watches due to the time and difficulty involved in re-bushing the barrel. This is the reason that many vintage watches have poor timekeeping and amplitude.
Here is the barrel bridge from the top side. Now we can begin.
Firstly, we must affix the barrel bridge to the main-plate and then mount that in the face-plate of the lathe. The hole opening for the barrel arbor needs to be dead center. If the hole is not dead center our cut will be off and the barrel will sit lopsided when in place. I am sure you can imagine that the tolerances are very tight inside a watch and a lop-sided barrel would cause dire consequences of time-keeping and power flow. The brass stick you can see here is called a wobble stick. We use that to find dead center.
The wobble stick has a point on both ends and is inserted into the barrel arbor opening. As the work-piece is turned in the lathe the stick will move or ‘wobble’ up and down. This wobble indicates how out of true the work piece is.
We then measure the amount of wobble at the other end. When the stick reaches its lowest point, the main-plate is gently tapped true. The work is centered once no wobble remains. The wobble stick is a very simple, yet incredibly precise way of determining the center of an object.
Once the center has been found the hole can be bored to the correct diameter.
Below is the bridge after the hole has been bored out.
Another view of the new hole.
Now the hole has been cut we need to install a bushing. I start with a rod of brass in the lathe.
I then turn the brass down and straighten up the end of the rod.
Measuring as we go.
Once the work piece is very close to the side it needs to be, I can cut a cone shape in the end of the piece. This gives me a guide for later drilling.
Once that is complete I can begin to part the piece off to size. I undercut it like so.
Carefully making sure to have a smooth even finish on both the inside and outside. At this point I also finish the outside diameter to size. I can then drill the hole to slightly smaller than I need. The bush will naturally come off as I drill because the drill is larger than the cone shape at the back.
The bush is then reamed to the final size and smoothed out. I can then fit in in the bridge. Here is the underside picture. I also cut a small chamfer around the inside of the hole.
Here is the bushing on the bridge side.
And we are done!