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 Post subject: Advice needed on spring length
PostPosted: Fri Mar 09, 2018 5:06 am 
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Victor I
Joined: Sat Apr 21, 2012 6:33 am
Posts: 129
Location: France
A friend of mine needs to install a spring in a barrel for a large clock but he has no clue on the length of the spring he has to find. So, is there a formula or a way to estimate the length of a spring based upon the barrel diameter?
Thanks for your help,
Jeff


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 Post subject: Re: Advice needed on spring length
PostPosted: Fri Mar 09, 2018 8:05 am 
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Victor III
Joined: Tue Jun 24, 2014 10:12 pm
Posts: 652
Once the spring is inside the barrel, the unwound spring should occupy about one-third of the radius from the center of the barrel to the barrel wall. This gives enough room for the spring to be wound and supply an equal force while the clock is running. This corresponds to about 6 turns of the spring inside the barrel. I do not have a formula for calculating the length. My source is a standard reference work for the watchmaker, "Practical Watch Repairing," by Donald de Carle, p. 83. I would continue to look for a formula, however. it would depend on the thickness of the mainspring and the diameter of the barrel. But perhaps the above can be used to make a reasonable estimate of the length.


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 Post subject: Re: Advice needed on spring length
PostPosted: Fri Mar 09, 2018 5:51 pm 
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Victor III
Joined: Wed Aug 01, 2012 8:43 pm
Posts: 726
If you know the make and model of the clock, many clock parts suppliers list the spring sizes required. Installing the wrong spring can cause much wear on the movement. Too thick or even too long will not be good. Spring strength increases exponentially with thickness.

If you can tell me the make and model, I may be able to offer more help.
Dave D


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