Mainspring

[Kalanag]

 

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 February 3, 2023 by Kalanag

[watchweasol]

Must admit that I would go with Pennmans figures, more modern thinking. In the watch and clock encyclopeadia  there are two pages on this matter.  Watch and Clockmakers Handb ook-----Dictionary and Guide  by F J Britten.       a book worth having as it contains a wealth of data,

[HectorLooi]

Ok.....

So..... Is the rule of thumb guide that the unwound mainspring should be 3X the diameter of the barrel still good?

[Willow]

thanks everyone for their comments and pictures of the spring and barrel I have a better understanding of it now and your comments have helped me a lot, once again thank you all.

[watchweasol]

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.

[oldhippy]

That means if you play by there strict rules then in many cases you might never fit the correct mainspring. These days as you know there is a limit on springs available, so you have to go for the nearest that is available.   

[watchweasol]

You are correct Old Hippy. You are limited as to what’s available  in the market place. And the closest you can get for the clock/watch you are working on as you say you may never fit the exact spring as it was made with.

[Kalanag]

11 hours ago, HectorLooi said:

So..... Is the rule of thumb guide that the unwound mainspring should be 3X the diameter of the barrel still good?

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

[Willow]

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

[oldhippy]

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.  

[Kalanag]

Interestingly the thicknes of the spring pack complies with the 1/4 rule of thumb:

[HectorLooi]

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.

[Kalanag]

2 minutes ago, HectorLooi said:

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

Oh yes sorry! I misunderstood you! 

[praezis]

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

[oldhippy]

You should never fit a mainspring that is to strong or long. Firstly to strong will cause excessive wear and affect the regulation, to long and you will only be using part of the spring.