Hermle Barrel Mainsprings

I see many Hermle movements in clocks. I have quite a few in my discarded storage area. They are from Germany but are newer movements and not made to overhaul. If yours is worn out then a new movement is installed.

They do have one good feature regarding the mainsprings that power the clock. The mainsprings are contained in a "barrel". You can take the barrels out of the movement without disassembling the whole movement. This makes it easy if you have a broken spring and want to replace just the spring.

The first thing you want to do is power down the clock. This is the most important thing in clockwork, so you do not get hurt and neither is there any cause for damage to the clock. Having a let down key is handy but if you do not have one, you can use the clock key. You want to put the let down key on the winding arbor. Turn the arbor slightly toward the winding direction to release the click paw from the ratchet wheel. Press up on the other end of the paw with your thumb. Press enough that the paw is away from ratchet wheel so the wheel can turn and let the key in your hand turn slowly. Be careful not to let the key get away from you. Slowly let the spring unwind. There will be a lot of force against the key in your hand. Having a let down key will make it a lot easier to unwind because of the smooth handle. If you are using a key, the wings will get in the way. Which means you will only be able to let down a couple of teeth at a time. You will have to continually stop and start letting down the spring.  

After the power is totally off the spring you can start to remove the barrels. The winding arbors have a bracket with screw around them that is holding the click wheel in place. By taking the bracket and click wheel off, you are now able to pull the winding arbor straight out toward you. Take notice of the groove along the winding arbor. When you later install it, the groove will have a position inside the barrel. The springs in the same clock could have different strengths so be sure and check the numbers on the outside of the barrels. Now you can install new barrels and reverse the whole process.