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Brendan sent in this Rolex Prince from the 1930’s complaining that the crown felt detached from the movement when trying to set the hands.
The movement is removed from its case and the dial and hands are taken off to investigate what is causing the problem. I test the keyless works and it is observed that when the crown is turned in hand setting mode the sliding pinion falls below the intermediate winding wheel making setting the hands impossible. Under the microscope it is just possible to see the end of the stem moving about on the other side of the movement.
My colleague Frank always turns up to our Guild board meetings with funky self-made watch parts, and I was getting curious. He told me that he had a CNC mill, and I pestered him to let me visit him to have a look.
Frank graciously let me come to his workshop, and this is where my little adventure starts.
As in many other fields, data is a very important matter. We have to find our spare parts, adjust the timegrapher to the correct lift angle, etc., so it’s very important to have the right data at hand.
So far, Generale Ressorts published a printed catalogue a very long time ago, and that’s still the only source of data when it comes to matching mainsprings with movements. There are some suppliers that have entered some of this data (Cousins, Ofrei, Boley) into their own systems, but a generally available list of mainsprings and where they fit wasn’t available anywhere.