![]() ![]() The mainspring barrel and arbor would then have been made the correct size to accommodate the spring and the hard work was done.įor more modern movements it is possible simply to look up the correct mainspring in tables of data, but for older watches this is usually not possible. How to determine the correct dimensions, width, thickness and length, of a mainspring? It might be thought that this is a problem for the designer and manufacturer of a watch movement, and indeed when designing a new calibre a manufacturer will have determined the correct section and length of mainspring for it, by calculation or more likely from experience, and have tested that it worked as expected. To replace the spring, you need to know what size to use. Modern white alloy “unbreakable” mainsprings rarely need replacing, but watches that I work on from the early twentieth century have carbon steel mainsprings which need to be replaced because they are tired and “set”, and are also very prone to breaking, which releases a lot of energy that can break pivots and jewels. In this case, a watch repairer has formed a hook in the end of the spring by annealing it and bending it over, catching a short piece of spring in it. The resilient hook is usually made by riveting a short length of material to the end of the spring. The outer end of the spring has a ‘resilient hook’ which bears against a step formed in the barrel wall. The middle part of the arbor is increased in diameter so that the inner end of the spring is not overly stressed, and the hook is recessed so that the second coil of the spring can lie on top of the first without the hook causing a bulge. ![]() The inner end of the spring has a hole which catches on a hook on the barrel arbor. The image here shows a mainspring in a going barrel. In watches with "motor barrels" the arbor drives the centre wheel and the barrel is turned to wind the spring. To wind the watch the fusee is turned, drawing the chain back and making the barrel rotate about its arbor, which is fixed, which winds the mainspring. As the watch runs and the fusee turns, the chain is drawn off the fusee onto the barrel. Teeth on the bottom of the fusee drive the centre wheel. In watches with fusees the outside of the barrel is smooth and one end of the fusee chain is hooked onto it. To wind the mainspring the arbor is turned so that the spring is wound around the arbor. In watches with "going barrels" the barrel has teeth on its outside that drive the pinion of the centre wheel. In engineering terms it would be called a boss or hub. In Swiss French it is called the “bonde”, which translates literally as bung or plug. Sometimes it is called the “arbor collet” to distinguish it from the arbor itself. In English watchmaking, the larger diameter part that the mainspring hooks onto is usually called the arbor. This larger diameter element is usually made as part of the barrel arbor, but it does not have to be it can be made as a separate part. The barrel arbor is made larger in diameter where the spring hooks onto it so that the spring is not bent too tightly. By turning the arbor or the barrel the spring can be wound up, storing the energy that makes the watch run. The inner end of the spring is hooked onto the arbor, a shaft around which the barrel can turn, or which can turn inside the barrel. The outer end of the mainspring is hooked to the inner wall of the barrel. It is a spiral strip of metal contained in a circular enclosure called the barrel. The mainspring is the power source for the watch movement. Bocks and Rams: IWC and Stauffer Trademarks.New product: Leather and Sterling Alberts.Savonnette and Lépine Watches and Cases.Converted Wristwatches - Transitional? No.Bears Galore! Three Bears and 0♹35 Silver.Rotherham & Sons Hermetic Wristwatch New.Borgel 2: Taubert & Fils and Taubert Frères.Borgel 1: François Borgel and Louisa Borgel. ![]()
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