Getting a new white alloy mainspring for a fusee movement

[GregG]

I made a topic a while ago about a warped and crooked barrel.

I am planning on making a new barrel.  After looking at the original barrel, I think I know what may have happened.  If you zoom into some of my pictures in the post, you can see that there is a square section, with a crack above it where the largest distortion is, and a circular section to the left of it. 

Many of these fusee movements I've worked on have a "hook" riveted onto the mainspring, which fits into a matching slot in the wall of the barrel.  I don't have a picture of it on the inside of this particular barrel, but it looks like whoever tried to repair it clipped off the end of the mainspring, and soldered it in place.  Then, they riveted on a hook that protrudes into the barrel, and used a mainspring with a hole in the end.  So basically they switched where the location of the hook is; connected to the mainspring vs connected to the barrel.

In between feedings and diaper changes for my first born baby (Nov 9th  ), I am going to fabricate a new barrel, and I want to use a proper mainspring, since the one that I received with it is definitely not the correct one.

First thing's first: unless I'm mistaken, I know I will have to make some modifications to the mainspring, since the fusee cone is designed to hold up torque at the low end of the mainspring, but modern mainsprings already have that feature built in with the reverse curve.  This means that I will have to clip off the reverse end of the mainspring, and rivet my own solution to fasten it to the barrel wall.

Based on the dimensions of the barrel (which has a 13.4 mm internal diameter), the original mainspring was likely between 2.00 to 2.05 mm tall, 0.15 and 0.175 mm thick, and 350 to 400 mm long.  That only leaves seven possibilities of currently-available mainsprings:

Next is the fact that white mainsprings are probably stiffer than carbon steel mainsprings, which means I'll have to size the thickness down.  By how much should I size it down? 

And the last thing that I can think of, the mainspring has the be long enough and wind enough times so that the fusee chain will eventually hit the stop works.  If I choose the first mainspring in that list, realistically will trimming off the reverse coil still give me enough length to make sure that that happens?

I'm sure there are other factors I am missing here.  Please let me know if this is a reasonable idea, or if I should just bite the bullet and use the replacement mainspring that came with it.

Edited November 20, 2024 by GregG
Changed title

[GregG]

Quick update: the Waltham 2230 mainspring is nearly a dead ringer for a mainspring. 2.05 mm high, 0.14 mm thick, 380 mm long. I know the strength isn't up to what it should be, but this is probably better than nothing, and a new one will probably beat the tired mainspring it currently has.

The problem here is that all the 2230 mainsprings I can find are NOS; carbon steel, made 60 years ago, and packaged in those paper sleeves, and everywhere I can find warns against using them because of potential micro-fractures from rust which could easily turn into macro-fractures and damage. I did find a few people selling white-alloy 2230's, but I have no idea if they have the reverse curve or not.

[oldhippy]

If the spring has rust on it that should tell you never use them as they are inferior.  

[GregG]

What would your suggestion be?  I'm guessing most white alloys will have a reverse curve.  There's got to be some consensus about the realistic safety of NOS mainsprings.  I understand that mainsprings with rust should never be used, but how often do they contain rust right out of the package?

[oldhippy]

You are correct about the white alloys. I think you are going to have to look around. Do you have any watchmakers near you? I retired from watch clock making back in the late 80's and I had a vast stock of material including individual springs wound with wire around them, so they do exist so an old watchmaker is your best bet.   

Springs rusty out of the package I would say they had been stored in a damp place. 

[GregG]

Unfortunately I don't think I have one near me.  At least not a dedicated one.  There's a jeweler about 10 minutes from me. 

Are the NOS springs more likely to break the further you wind them, or are they equally likely to break at any amount of wind?  It's more for the provenance and appreciation than anything else, so it's not like I'm going to wind it to full capacity for it's excellent timekeeping ability.

[Neverenoughwatches]

3 hours ago, GregG said:

Unfortunately I don't think I have one near me.  At least not a dedicated one.  There's a jeweler about 10 minutes from me. 

Are the NOS springs more likely to break the further you wind them, or are they equally likely to break at any amount of wind?  It's more for the provenance and appreciation than anything else, so it's not like I'm going to wind it to full capacity for it's excellent timekeeping ability.

The problem with nos springs is that you don't know what you are getting, besides the fact that they are unused old stock and probably have little chance that they have anything new about them. A rusty looking spring is just that and should never be used, a spring that has micro fractures again is just that unfortunately you wont know that without looking at it under high mag or until it fractures under tension in the barrel sometimes spectacularly and possibly at any given moment during winding. To summarise a nos spring is an unknown quantity of age , quality and consistency. You can narrow down those risks by buying from a reputable supplier but still not remove them entirely. 

[GregG]

I tested out my new lathe and mill to fabricate the barrel.  I'm practicing on aluminum first because lead-free brass is more expensive.  Side note, I didn't think there could be a machine as messy as a mill.  There are aluminum shards everywhere.

I still have to dial in a few things with the lathe to get it running true, as my barrel ended up slightly taller than the stock one.  The width was dead true to the original, 14.50 mm.  Overall, I'd say this was a pretty good first attempt.

Edited December 6, 2024 by GregG