Fusee spring: right or wrong?

[brutusamiga]

Hello folks,

I got a wonderful top drawer triple fusee musical bracket clock in.

All three springs are exactly the same. They are equally long and the same strength and width. The music (chime) barrel is much bigger than the strike and time barrels. When fully wound there is about 70% space left in the barrel. This tells my that obviously the spring is not original. BUT, assumption is the mother of all...

The clock was made to only play 30 seconds of music on the hour. It does not chime every 15 minutes.

The three springs look and feel old and are probably original.

I have a few experts telling me the spring is correct and should not be replaced. These people are much more experienced than me but my gut is telling me I must replace the spring with a longer one. Why would such a short spring go into such a huge barrel?

Your thoughts please.

Bernard

 

[John MacArthur]

Those springs look pretty well "set" to me. I'd get new ones, being careful to get them the same dimensions, especially the thickness.
Johnny

 

[brutusamiga]

The springs are set and I was planning on replacing them. But I have never heard of a chime barrel spring that is exactly the same dimension as the time and strike springs especially with a barrel that is substantially larger than the time and strike barrels. The 3 fusees and the fusee chains are exactly the same.

 

[shutterbug]

There are several spring size calculators that appear here if you search. One of them would be useful for finding the correct length for your larger barrel if you know the thickness.
Springs confined to barrels for many years will take on a 'set' appearance even when they are fine. I have found that the original spring is usually of much better quality than any modern replacement, and am very conservative in replacing them. I usually replace only if the spring is either corroded or broken, and I don't have problems with that decision.
Here's one calculator that you can play with

 

[Uhralt]

If the chime spring provides enough power to run the chimes for 8 days I wouldn't replace it.

Uhralt

 

[Ralph]

An optimum sized mainspring, assuming the correct strength, should fill half of the available barrel volume.

Some musical clocks chime only three times a day. and not hourly. Some only six days a week. They shut off on Sunday.

There are some good tools for spring sizing, not easily found at

http://www.nawcc-index.net/

Under "Horological Links"
>Repair & Restoration
>Adjustment & repair
Methodology
>Calculations


Ralph