Hairspring Replacement / Swap

[rodabod]

Hi,

I needed a spare hairspring for an early IWC cal 83 bimetallic (split, temperature compensating) balance. I had a spare cal 83 monometallic (the later non-split, incabloc) balance which I borrowed the hairspring from. 

With the later hairspring, the balance is now oscillating too fast. Around 30 minutes fast per 24hrs. I can only presume that the earlier balance wheel is lighter. The hairspring looks to be working ok, ie. none of the coils are touching each other and the amplitude is good. 

The only option I can see is to add weight to the balance wheel, but I don't think this is a possibility for this balance wheel as there are no "quarter" screws or "mean time" screws to adjust the rate without changing the temperature compensation. 

I want to use an earlier bimetallic balance wheel, so is my only option to acquire a rare hairspring, or is there a way to add weight to this wheel without disturbing the temperature compensation?

Edited April 19, 2017 by rodabod

[szbalogh]

Maybe You can just unscrew some adjustments screws on the balance a bit which will increase the inertia. But You have to poise it again. I dont know how much change this does. Might be not enough.

[watson1]

On 20/04/2017 at 9:39 AM, szbalogh said:

Maybe You can just unscrew some adjustments screws on the balance a bit which will increase the inertia. But You have to poise it again. I dont know how much change this does. Might be not enough.

Are the screwed weights a friction fit?

Can they be screwed out slightly and not fall out later?

 

I have seen some photographs with some weights on longer screws. Are these long screw versions intended for adjustment?

Are the threads tighter to allow for not being screwed in till tight?

[praezis]

On 19.4.2017 at 10:47 PM, rodabod said:

Hi,

I needed a spare hairspring for an early IWC cal 83 bimetallic (split, temperature compensating) balance. I had a spare cal 83 monometallic (the later non-split, incabloc) balance which I borrowed the hairspring from. 

With the later hairspring, the balance is now oscillating too fast. Around 30 minutes fast per 24hrs. I can only presume that the earlier balance wheel is lighter. The hairspring looks to be working ok, ie. none of the coils are touching each other and the amplitude is good. 

The only option I can see is to add weight to the balance wheel, but I don't think this is a possibility for this balance wheel as there are no "quarter" screws or "mean time" screws to adjust the rate without changing the temperature compensation. 

I want to use an earlier bimetallic balance wheel, so is my only option to acquire a rare hairspring, or is there a way to add weight to this wheel without disturbing the temperature compensation?

Don't worry, you already did disturb the temperature compensation, after mounting a wrong (compensated) hairspring on the split balance! So adding weight will not make things worse...

Frank

[rodabod]

I ended up adding timing washers to the “quarter screw” positions, except just at the balance arms so as not to affect temperature compensation further. I then had to poise the balance which was adjusted in five positions. 

It was an awful lot of work.