Balance Spring Replacement

Posted: Sat Dec 11, 2010 1:24 am     Post subject: Balance Spring Replacement

I damaged a balance spring on on a 40's Westclox alarm clock I've been working on. After much work trying to corrcet the spring's shape I decided to buy a spring assortment and try a new one. I found the most similar one and attached to the staff with shellac for a friction fit collet to staff.
I unwound the old one measured its length and using the spiral formula calculated the length of the replacement. I removed the difference in the two lengths so my new spring was the same length as the old one. The new one fits through the regulator slot nicely when anchored however it has 7 loops where the old one had 8. The clock loses time. With the old spring (it gained time).

My question is:
Is it correct to only match the springs in terms of length and diameter or is the number of windings also important? Obviously if I want this spring to fit properly through the regulator, less length is a problem.

thanks

Posted: Sun Dec 12, 2010 5:52 pm     Post subject:

with this type of spring it important to get a replacement the same thickness too.

Posted: Mon Dec 13, 2010 1:03 am     Post subject:

thanks. I didn't consider the thickness.