Mainspring and barrel


    The mainspring provides the power for the movement,  it is one of the most important and and frequently overlooked parts of a mechanical timepiece.  The mainspring is contained in the barrel and wound by the arbor.  The barrel components consist of the barrel and the barrel cover which have bushings in them through which the arbor is held in place.  The barrel arbor has a small hook on it which catches the hole in the end of the mainspring and the arbor also has shoulders on which the barrel is carried and pivots on it’s ends that hold the barrel complete in place between the barrel bridge and pillar plate.  The arbor also has a square on it’s top end and is drilled and tapped, this square accepts the square in the ratchet wheel and a screw holds the ratchet wheel in place on the arbor.


    The barrel complete is held between the pillar plate and barrel Bridge.  The barrel bridge is held in place to the pillar plate by screws and steady pins.


    To remove the barrel, first remove the ratchet wheel, now remove the bridge screws, then the bridge can be popped up using edge of screwdriver.  Most movements have notches cut into the edges of the plates and bridges to accept the blade of a screwdriver to release the bridge from its mating surface.  After the barrel bridge has been removed the barrel can be

    To remove the mainspring from the barrel you will have to pop of the cover.  To remove the cover place the blade of a small screwdriver into the cutout in the edge of the cover and pry the cover up carefully until it pops off.  Some barrel covers do not have a notch and need to be popped off by pushing on the arbor from the opposite side.


    After the cover has been removed use a pin-vise to grip the top pivot of the arbor and remove the arbor with a twisting motion.  The mainspring can then be removed by pulling up on the center coil with a sturdy pair of tweezers until the coil clears the top of the others, then carefully allow the mainspring to slowly unwind out of the barrel using your fingers, taking care not to allow the spring to suddenly pop out all at once.

Some common mainspring end types pictured bellow


Mainspring shapes pictured bellow