How do I let down the mainspring on this fusee?No ra (2024)

So far I have only removed the dial and motion work. No mainspring ratchet and click. This movement has the worm under the mainspring barrel to add tension. I could remove the balance co*ck and balance spring, then let the mainspring down slowly through the train--there's not much tension on mainspring; I checked. I've certainly done this before and don't see a problem.

Is there a different way?

John

Hi John,

You need a key slim enough to fit the square on the tangent screw (worm), and simply turn it anticlockwise to release the spring tension. You may have to modify a watch key to allow it to fit in the very narrow space available, or make a key from scratch. If you make a key, first turn down the OD enough to clear the plate and barrel, and you can probably get away with just drilling a hole the same diameter as the diagonal of the square, don't harden and temper it and it should grip well enough to turn the worm.

Regards,

Graham

Graham:

Back from weeding. The rain a few days ago has given over to a relief in temperature. If the weather keeps up (and I keep up) I will do more outside work.

Anyway, let me see what sort of keys I might have that fit. I got a quite a few. You've already answered one additional question--"anticlockwise."

I know when tension is off the mainspring . . . when the chain goes slack?

John

jboger said:

I know when tension is off the mainspring . . . when the chain goes slack?

Click to expand...

Yes. The chain is all on the barrel so you won't need many turns of the worm.

It can be dangerous to let down a fully wound watch this way as all the force of the spring is on the worm/wheel which, if previously abused, might well result in the mesh not being very good. It'll hold the tension while stationary but start unwinding using the worm and it might let go, stripping all the teeth off the wheel.

Dear Mr. Kennedy:

Are you writing that, in general, the best way to let down this sort of movement is through the train? I can securely stop either the contrate wheel or the third wheel, lift up the balance co*ck, unpin the balance spring, and go that route if it's the safest.

I do not know the history of this watch other than that it probably runs but is very dirty. It looks to have been neglected for many years.

John

Graham, Seth:

Here's what I did. I found a small key that easily slipped over the square of the tangent screw. And then I gave a small (less than a quarter turn) counter-clockwise turn to see the effect it had on the chain--no effect! After two or three full turns, I again tested the tension on the chain--it was looser! Progress! All in all it took at least six full turns for the chain to go lax.

But the chain was still hooked. You see, even when the movement was completely wound down, there was still tension on the chain, as there should be. This meant the fusee end of the chain was pulled fully over to the mainspring barrel, making it hard to unhook the chain. So with my thumb I rotated the barrel slightly in the direction of the fusee. This allowed the hook to pop out of the slot at the base of the fusee.

You can see the hook peeping out in the attached photo, thanks to both of you.

John

Yes, that all sounds about right. If the hook is stubborn on the fusee you could keep turning the worm until you can ''wind' the fusee that 1/4 turn or so, such that the hook is at the outside edge of the movement and easier to get at.

Consider that one full turn of the worm equates to rotating the wheel on the barrel by one tooth. And there are a similar number of teeth on that wheel than there are on a later (dare I say, 'normal') set up ratchet wheel. So six turns, ie six teeth, would be pretty ordinary, ie around 1/3 to 1/2 of a turn of set up on the barrel arbor.

Hi John,

SKennedy said:

And there are a similar number of teeth on that wheel than there are on a later (dare I say, 'normal') set up ratchet wheel.

Click to expand...

About 15 or 17 teeth is usual, so progress can seem slow compared to a ratchet and click.

When you remove the wheel from the barrel arbor square, have a close look at the teeth to check if there's any damage; the wheel is brass and if it's been roughly handled the steel worm can easily damage teeth, as Seth has pointed out in his post #4.

Regards,

Graham