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Finding the correct mainspring

SndChsr

By SndChsr
in Watch Repairs Help & Advice

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SndChsr Watch Enthusiast

SndChsr

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Hello everyone,

I'm working on an old cylinder movement watch. I have no idea who made it, where it came from or how old it is. There are no markings on the dial or any of the movement plates/parts. It appears to be mid 19th century. The mainspring however has lost pretty much all its elasticity. Out of the barrel it looks pretty much the same as it would inside the barrel, but after 200yrs or so, that's to be expected.

I'm having issue locating a replacement. I have measured it and these are the dimensions (metric):

Height - 2.24mm

Strength - .20mm

Barrel Diameter - 16mm

Hole End 

Could somebody point me towards finding such mainspring, or is there an alternative that would work?

Thank you for any help with this.

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JohnR725 Distinguished Member

JohnR725

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You forgot to mention the length of the spring? Then the 2.24 mm is not going to find that it looks like it's going to be 2.20 mm looking in the mainspring catalog. Then finding a replacement mainsprings for watches made before anything resembling Standards can be a challenge. Somewhere are likely off till longer spring and put a hole in it yourself.

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SndChsr Watch Enthusiast

SndChsr

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Thanks John. So correct me if I'm wrong please. I thought that the length of the spring can be substituted by the measurement of the spring barrel diameter(?) where then a selection of the spring fills only 1/3rd of the barrel. 

In order to measure the length of the mainspring, I would have to straighten the spring out, and if that's the case, the spring would be ruined completely, and if no replacement is found, I would not be able to even use the original spring, as much a bad shape it is in.

Is there a safe way to measure the length of the mainspring?

Thank you.

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JohnR725 Distinguished Member

JohnR725

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2 hours ago, SndChsr said:

I thought that the length of the spring can be substituted by the measurement of the spring barrel diameter(?) where then a selection of the spring fills only 1/3rd of the barrel. 

Yes there are formulas but I is find it easier if I have the existing spring to measure it. If you're worrying about destroying it which in your case you definitely should be then well I guess will have a problem. Usually in stretch it a little bit as I would rather go with the length of the original spring. But before you get worried about things that the carbon steel spring and the modern Springs are different and depending upon who you talk to most of us think the modern Springs are stronger so you want to go for a lighter spring perhaps.

1 hour ago, watchweasol said:

catalogue for GR mainspring

This is one of the things you want to have because when I looked up your width I went here and that's what I discovered you can't have the fractional millimeter and there's a page plus of mainsprings within the strength range you need but I couldn't tell about the length.

 

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SndChsr Watch Enthusiast

SndChsr

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10 hours ago, JohnR725 said:

Yes there are formulas but I is find it easier if I have the existing spring to measure it. If you're worrying about destroying it which in your case you definitely should be then well I guess will have a problem. Usually in stretch it a little bit as I would rather go with the length of the original spring. But before you get worried about things that the carbon steel spring and the modern Springs are different and depending upon who you talk to most of us think the modern Springs are stronger so you want to go for a lighter spring perhaps.

This is one of the things you want to have because when I looked up your width I went here and that's what I discovered you can't have the fractional millimeter and there's a page plus of mainsprings within the strength range you need but I couldn't tell about the length.

 

Thanks again John. Much appreciate your detailed answer. I'll give it some thought regarding the length of the spring. I may have no option but to destroy it in order to get the correct length. 

Many thanks for everyone's generous replies.

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jdm Distinguished Member

jdm

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51 minutes ago, SndChsr said:

 I may have no option but to destroy it in order to get the correct length. 

That's never necessary. There are formulas to calculate length when it's in the barrel e.g. https://theindex.nawcc.org/CalcMainspringLength.php

And when it's outside just use a cotton thread along it.

Anyway, a difference like 5% in normally negligible.

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JohnR725 Distinguished Member

JohnR725

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22 minutes ago, jdm said:

That's never necessary.

A unfortunate problem In watch repair is accidents happen. But there is no need to deliberately Destroy something to figure out the length of the mainspring. I suspected somebody would come along and point you in the direction of the formula  which will get you close and you don't have to be that close.

 

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SndChsr Watch Enthusiast

SndChsr

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16 minutes ago, JohnR725 said:

A unfortunate problem In watch repair is accidents happen. But there is no need to deliberately Destroy something to figure out the length of the mainspring. I suspected somebody would come along and point you in the direction of the formula  which will get you close and you don't have to be that close.

 

Looks like JDM just did! 🙂

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SndChsr Watch Enthusiast

SndChsr

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42 minutes ago, jdm said:

That's never necessary. There are formulas to calculate length when it's in the barrel e.g. https://theindex.nawcc.org/CalcMainspringLength.php

And when it's outside just use a cotton thread along it.

Anyway, a difference like 5% in normally negligible.

Sorry for sounding like a dunce but on that calculator, are the measurements in millimeters? 

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jdm Distinguished Member

jdm

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3 hours ago, SndChsr said:

Sorry for sounding like a dunce but on that calculator, are the measurements in millimeters? 

Millimeters, or English system, o French lignes, or that special unit that Americans used for their mainspring, we are technical people and must be able to figure out and convert as necessary. Otherwise it can happen like the current UK gov.t did to justify restoring the old system: "people doesn't know how much a pound of apple cost".

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SndChsr Watch Enthusiast

SndChsr

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On 9/25/2021 at 6:01 AM, jdm said:

Millimeters, or English system, o French lignes, or that special unit that Americans used for their mainspring, we are technical people and must be able to figure out and convert as necessary. Otherwise it can happen like the current UK gov.t did to justify restoring the old system: "people doesn't know how much a pound of apple cost".

Haha...that's what I thought. Looks like the correct length would be 460mm, or 46cm. Sounds about right. Thanks for helping with this!

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