A common wear point on the Omega 861/1861 caliber is the upper barrel hole in the mains plate. When the watch is wound the pressure from the arbor (which is made of steel) is exerted onto the side of the hole in the bridge. The bridge is made of brass so that is the first to wear, as brass is softer than steel. Generally, the service centres will put a new barrel bridge in the watch, but at Precision Horology we repair the existing bridge so that we don't hav to needless exchange large components. The work involved in doing this is included in the overhaul cost, the customer only pays for the new bushing.
Here is the infamous movement in question.
You can see the hole has worn away. This example is by no means the worst I have seen. When it's really bad the barrel will actually make contact with the centre wheel causing amplitude and time-keeping issues.
Here we have the bridge, arbor and new bushing. We use an existing bushing manufactured by Omega. It needs to be modified for our purposes here, but it's the closest we can get. A big thank you to Al at Archer Watches for giving us the bushing reference to use here.
We first ream the hole out using the jeweling tool. We don't need to worry about the concentricity of the hole being off as the barrel arbor doesn't stick all the way through the hole so we have factory centred hole that we can follow. We use lubricant on the cutting tool to make the process easier. If the arbor comes all the way through the bridge we need to mount the piece in the lathe and find centre before making any cuts.
We then friction fit the bushing into the plate using the Horia tool to press it in place.
The bushing is in.
The hole of the busing is too small for the barrel arbor, which is where the modifying comes in. We can ream the inner hole to size now.
We finish it off by hand with a smoothing broach so we end up with a nicely polished surface which reduces friction when winding.
Once complete we check the barrel arbor for fit and we have a repaired barrel bridge ready to use once again.
