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Mainspring


Willow

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40 minutes ago, watchweasol said:

Hi Guys  find attached pages from Laurie Pennman (Master clockmaker) and his calculations for the mainspring acommodation as regards to the barrel fitting…

Exactly what @praezis explained 🙂

Edited by Kalanag
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Hi. As a rule of thumb Iwould say so as the spring needs space to operate. But the actual data for springs in barrels is calculated as Lauri Pennmans formula in his book for exactness and confirmed by Prazeis (Frank) who also came to the same conclusion with his calculations.  So in conclusion Pennman/Prazeis are correct and De Charles theory is just a guide.

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As promised hear is a photo of the spring in the barrel you can see how tight it is, now the question is when i order a new spring do i get a thinner spring, shorter spring, even a different height spring or all three, thanks for your patience

20230204_122242.jpg

20230204_122253.jpg

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It looks a little long and from the angel of the barrel looks as if it could be a little higher. From what I can recall the springs in these movement are very strong so a little less strength should be fine. Don't have it to high you do not want it rubbing the inside of the barrel cap.  

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6 hours ago, Kalanag said:

As @praezis an Laurie Pennman calculated correctly the rule of thumb should be 1/4 instead of 1/3

I was referring to the guideline for testing if a spring is "set".

 

2 hours ago, Willow said:

As promised hear is a photo of the spring in the barrel you can see how tight it is, now the question is when i order a new spring do i get a thinner spring, shorter spring, even a different height spring or all three, thanks for your patience

The spring looks a little long. I'm wondering if it would be possible to cut off 2 or 3 coils then anneal and reshape the cut end.

But looking at the coil, it should be able to take a lot more than "two or three" winds. I think the problem lies elsewhere.

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I searched my library for mainspring rules.

None of the celebreties mentioned in this thread invented those rules themselves. They were taught it and passed that knowledge in their books.

In fact some old books mention such 1/3 rule while the exact dimensioning of mainsprings was already known and published for a long time. Seems it was a rule of thumb among craftsmen who were more busy with file and lathe than with books.

The rule for a maximum of barrel revolutions that determines the optimal length of a mainspring was published by Rozé in 19th century. Claudius Saunier mentions this in his comprehensive textbook (paragraphs 1211-1216) from 1861. I also found this rule in books from 1902 and 1923. So Mr. de Carle could have known better. 

Nevertheless a watch or clock with a too long mainspring will run its 24 hours and so supporters of the 1/3 rule were contented.

Frank

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