Swap Hairspring

[PostwarO27]

In my limited experience in watch tinkering, I've never considered what would happen if I swapped a balance hairspring from a watch with a vph of 21600 into a watch with vph of 19800.  I'm trying to get an old Omega caliber 620 running for my wife and having difficulty finding a hairspring for it.  Ranftt indicates that there are multiple variations of this movement in both 19800 and 21600 vph.  Could I take the hairspring from an 21600 vph movement (625) and put it in the 19800vph (620) movement?

Edited May 5, 2022 by PostwarO27

[nickelsilver]

You would have a very hard time swapping in a hairspring from another 19,800 movement, so pretty much impossible to get a 21,600 to work.

 

The springs are matched to the balance. In production the springs are colletted and studded at a specific length with the pinning points lined up for optimal timing, then their strength is measured and they are sorted into 20 groups. The balances are also sorted after poising into 20 groups, which correspond to the springs. They get mated up and off they go. If you look at a graph of the groups the majority are in the middle third, with fewer in the outer thirds; so there is a chance that if you get a spring from a balance that was originally in a close group, it might work. If you have a balance with screws you have much more adjustment to compensate for a mismatch. As this caliber has a solid balance with no screws, like I said, even with a 19,800 it will be a dice toss if it's even close.

[oldhippy]

The balance and hairspring work together in order to obtain good timekeeping. By changing to a different hairspring which has a different beat will cause regulation problems and the rotation of the balance wheel. 

Edited May 5, 2022 by oldhippy

[Nucejoe]

1 hour ago, PostwarO27 said:

what would happen if I swapped a balance hairspring from a watch with a vph of 21600 into a watch with vph of 19800.  

 Depends on the weight ( moment of inertia) of the donor and recipient balances and  likely to run strong and fast. 

[PostwarO27]

3 hours ago, oldhippy said:

The balance and hairspring work together in order to obtain good timekeeping. By changing to a different hairspring which has a different beat will cause regulation problems and the rotation of the balance wheel. 

It sounds like a balance complete is the way to go then.  Is that correct?  Is it also correct to assume that a donor movement may also not have a matched spring/balance in it?  Is it then good practice to always replace both spring and balance (balance complete) if the hairspring is damaged beyond repair or can a skilled watchmaker match to separate pieces together?

Edited May 5, 2022 by PostwarO27

[Nucejoe]

Yes, a balance best be vibrated with a compatable spring. Look up luthy tool for the task.

There has been discussions on this subject, heres one.

On 4/22/2022 at 6:09 PM, Nucejoe said:

  Providing a compatible and long enough hairspring, attach the stud and build your balance complete, instal in the watch and try regulating on TG, you will face one of the following cases.

1- Oscilator runs fast with regulator arm closest to beat adjustor. Weigth needs to be added to the balance, which is impossible on anular balance. 

2- Oscilator is regulable. proceed with regulating.

3-Oscilator runs slow with regulator arm farthest from the beat adjustor. Spring's length is to be shortened so you free to make an educated guess as to whereabouts to repin the springs stud, check the rate on tg to decide which direction you shoild inch towards to the right pining point. 

Do not cut the spring until you find the pining point. 

Mention was once made of the caspari effect by member praezis, which I do near the collet. 

Your further questions are welcomed.

 

 

 

[Nucejoe]

4 hours ago, PostwarO27 said:

It sounds like a balance complete is the way to go then.  Is that correct?  

Yes, a ready made  balance complete has been well poised, put in beat and vibrated to produce the right beat for your watch to show accurate time. Frankly just the poise alone is challenging in case you had to remove weight off of the balance just for a static poise.  Look up trueing a watch balance and poising tool.

Also in the following the guy is matching balance and spring. 

 

[Neverenoughwatches]

6 hours ago, Nucejoe said:

Yes, a balance best be vibrated with a compatable spring. Look up luthy tool for the task.

There has been discussions on this subject, heres one.

 

Hi nucejoe  .That was made to sound quite easy. What about choosing a hs size to suit the balance wheel ?

[spectre6000]

10 hours ago, nickelsilver said:

The springs are matched to the balance. In production the springs are colletted and studded at a specific length with the pinning points lined up for optimal timing, then their strength is measured and they are sorted into 20 groups. The balances are also sorted after poising into 20 groups, which correspond to the springs. They get mated up and off they go.

It's incredible how much art goes into such a scientific endeavor. The incredible metallurgy and machining that goes into such an insanely precise piece of machinery. Then the tolerances are so tight, that the touchy feely mix and match routine is the best way to assure accuracy. Things like this permeate watchmaking at every turn!

Edited May 5, 2022 by spectre6000