Too old, too dumb, and unwilling to invest

 

Every once in a while, we get a customer with an "un-fixable" watch. Something that requires a part or tool no longer in existence, an ungodly amount of man-hours, or an enthusiasm-eroding invoice estimation. An even rarer occurrence, a customer who faces all three roadblocks but is willing to proceed. The subject: a simple Piaget bumper movement from approximately the 1960s. The situation: after the watch sustained some compressive damage to its case, the caseback was no longer free enough to be removed for service. The watch had been taken to several watchmakers (some of the best in the country) in and out of Sydney with workshops of varying ability. However, it was met with the same response. Case back won't come off, too delicate to force off with the tools we have available, not willing to incur wrath if destroyed in the process. Let's be realistic, these are absolutely valid objections. The Piaget case and caseback are of solid gold construction, already making them quite soft and easy to deform (the issue in the first place), and it is very fitting of its era - thin and delicate. In no time at all, the wrong case opening tools will tank its value and leave lasting scars.

Unfortunately the Piaget did not make this easy for anyone. The case back had a raised dodecagonal platform that the humble Piaget watchmaker would seat a custom tool onto, to safely remove the caseback. Finding such a tool is a statistical impossibility. Making one is expensive and time consuming. So we got started right away. First, the caseback and case was measured to construct a landscape on which the custom tool would fit. Then, a design was drawn up for a tool to fit both the caseback and the bench mounted case back opener that the tool will be held in. What we want from the tool is close to an exact fit on the caseback so as to not mark or deform the shape as you would using the wrong size spanner on a bolt head. In theory, a 38mm dodecagon fits on a 38mm dodecagon but in reality it does not. The case back is already slightly deformed through the initial damage and subsequent unsuccessful removal attempts. On top of this, you would need maybe 10um (micron) clearance on the diameter for a very snug fit.

The last thing to take into consideration is the sharp corner between each face. Because we want the shape so close to match, we have to consider the radius of the endmill being used. This radius will be transferred to our Piaget tool, meaning even with enough clearance on the total size of the shape, the internal rounded corners of the tool profile would interfere with the external sharp corners of the caseback profile. A simple design feature known as a 'dog ear' (please email if you know what the correct name for this feature is called) is added to each corner. Basically the end mill used is programmed to move outside the profile such that the radius is no longer interfering. You can see here that Breitling is using a similar feature. The design was sent down to Brookvale to be realised.

The initial brass bar stock was turned down in our Shaublin lathe with a few of the features to fit the bench mounted opening tool. The entirety of the Piaget caseback side of the tool was milled in our Kern Micro HD after being design and programmed on Fusion360. Once finished on the Micro HD, the tool was brought to a manual turret mill to apply the last few features for the tool to fit into the bench mounted case opener. The raw tool is now complete. After some hand de-burring and chamfering, we were ready to give it a shot.

To say that it was an easy to remove caseback even with the custom tool would be a lie. The mid-case and caseback may as well have been welded together. However the tool (and I) eventually prevailed and the caseback was removed. One thing that may have made it more difficult than usual to open was the presence of a lead seal. Used before the ease of silicone extrusion became the norm, a thin ring of lead was used as its fairly soft nature allowed it to deform readily to seal the movement off from outside water, dust, and watchmakers. Nothing that a little bit of time, over two million dollars’ worth of machinery, two precision machinists, and a watchmaker can't handle.

The actual overhaul itself was fairly complex, but a nice movement to work on. Total hours from start of design to end of overhaul: 36 business hours.

Andrew