Mainsprings
Isochronism is the primary goal of every modern timekeeper. It is the characteristic of generating a constant, uniform period of vibration, to be able to assure a consistent rate of time. Although every part of a movement is important to achieve this, much of what can be made following the mainspring and barrel would be rendered ineffective if the mainspring is not well made.
Every mechanical watch requires a power source to drive the wheels that lead to the regulatory organ, which is in 99.9% of watch movements an oscillating balance wheel. The power source is a mainspring, wound either manually by hand through a winding crown, or by an automatic winding system…
incorporated into the watch movement. Although there are always exceptions to every rule in horology, there exist two fundamental types of mainspring. Those that when fully wound are blocked from turning, made for manually wound movements, and automatic mainsprings. Automatic mainsprings have a longer bridal fixed at their end which push against the inside of the last turn of the spring, approximately 20% thicker than the rest of the spring. This long bridal allows the mainspring to slide on the inside of the barrel (where the mainspring lives) once the spring is fully wound. This allows the automatic mechanism to continue to turn, continuing to wind the fully wound spring without causing any damage.
Mainsprings originally replaced weights used to power clocks to be able to render them both smaller and portable. They first appeared (approximately) in 15th century European clocks and by the 16th century in pocket watches. Since their conception, as with all elements found in horology from the most simple to complex, there have been considerable technological steps forward in their manufacture and efficiency.
Traditionally there were basic proportions by which mainsprings were made in relation to the barrels they sat into. These proportions were defined by the internal diameter of the barrel and the diameter of the barrel arbour (the arbour is the axel that winds the mainspring in the centre of the barrel, hooking onto the inner coil of the mainspring). These would lead to on average 8 turns of the barrel arbour until the mainspring was fully wound. Today however, with the development in watchmaking and the influences of modern construction and manufacturing techniques, there are many variations leaving the classical approach behind. This departure makes what is a complex component to produce, a far greater challenge to make. These variations may be due to the height of the mainspring which can be as small as 0.6mm or, to wider than conventional barrels, with mainsprings with an extended length of over 2 meters made to increase power reserve. The power reserve is the complete period of time the watch will run for after a single complete winding of the mainspring.
To learn more click here