A vintage watch without a correct hairspring is no longer a watch— it’s parts. If a hairspring is damaged beyond repair or incorrect (aka a past watchmaker failed attempt) then you either find a solution or tell the customer the watch is unrepairable which would be the most common response given by watchmakers today. I can typically bring these watches back to life but it requires a customer as committed to the watch as I am. Relative to solutions, if the watch is old enough (pre-1950’s) , you often can’t simply swap-in a balance compete— the balance staff, roller jewel, balance, and hairspring are often unique to the particular watch, balance cock, and escapement. Sometimes you can adapt a hairspring from a parts watch by modifying the spring and weight of the balance to get timing to an acceptable level. If none of this works or parts are unavailable, then you are left with no other option other than vibrating a new hairspring, a dying skill and art form. I have spent many years accumulating blank hairsprings because the spring strength and size specifications needed to satisfy a range of watch repairs is enormous. Once you identify a candidate spring, its own journey, then you need to go through a great many steps to fit the hairspring— flat or breguet— to the watch. In this picture, the hairspring has been selected through the process of hairspring vibration. The inner coil is formed to conform with mathematical requirements and to fit the collet appropriate for the balance staff. The painstaking process of pinning the collet to the hairspring is then undertaken. This must be done so that the spring is undamaged, level, and collet centered in the hairspring. This is much more difficult then it looks. Once this is completed, many steps remain to bring the watch back.
