pocket watch main spring

Quinn

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Feb 18, 2021
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I took apart my first barrel in an early 1900s Swiss pocket watch. The spring appears intact. The watch is a non-runner, so far the only thing I could see wrong was a blown fourth wheel jewel. The watch was wound as tight as it would go when I got it.

Since this is my first foray into a watch I wonder what to do with the main spring. For one I don't have the winding tools. I have heard the best thing to do is to replace the spring, although I am not sure how to go about purchasing the right one (I do know about cousins UK, I am in the US though and read various sources that it's hard to find which spring to get). I can measure the current one, but I read they are often replaced with what's at hand and not necessarily the correct one for the watch. I am aware of the main spring calculator spreadsheet also.

Any help appreciated. The spring was slow to unwind, didn't seem a lot of pep to it. Is that any indication it's "set" as I've heard of?

2021-02-28 10.54.39.jpg 2021-02-28 10.58.55.jpg 2021-02-28 11.00.00.jpg
 

Dave Coatsworth

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Hello Quinn,
Swiss mainsprings are readily available from suppliers here in the U.S. You just need to provide the width and thickness measurements and the length as close as you can. Your spring is what is known as a 'tongue end'. Check the 'sticky' post at the top of this Watch Repair forum.

You definitely want to replace that spring as it is what we call 'set'.
 

Quinn

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Thank you so much Dave, that is very helpful, and I will check the sticky topic.

Can I ask how you can tell that it's set? I disassembled a 2nd watch today (old Atlas movement rather corroded) that had the same feel when I unwound it. Pic attached of the Atlas.

Thanks!

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gmorse

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Hi Quinn,

A general rule of thumb is that the spring should expand to at least three times the inside diameter of the barrel when it's removed, and also that it should be flat and not coned. The latter condition is often caused by previous repairers mishandling the spring in removing or replacing it in the barrel. The hookings at each end must clearly be intact as well.

Measurement is critical; the width ideally should be just less than the inside height of the closed barrel, and the thickness must be as indicated by the spring calculators. Spring strength is directly proportional to the width, but to the cube of the thickness. The length is important but much less so than the thickness. A micrometer is a more accurate instrument than a vernier for measuring the spring thickness.

There's been much debate around the difference between the old blue steel springs and the modern alloy ones regarding their relative strengths and the advisability of fitting blue steel ones, but since the alloy ones are all that's available as new stock now, and any new old stock' blue steel springs will have been in their restraints for very many years, the new ones are recommended. These 'NOS' steel springs can fail dramatically when they're first wound, potentially causing other damage to the movement.

Inserting a new spring without the use of a spring winder, (which is the recommended way), is possible with care, but does risk introducing coning.

Regards,

Graham
 

Quinn

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Thank you all for your wisdom! I will measure the springs, I do have digital calipers 0-150 mm, is that good enough?

I would not want to install the spring by hand, I have read it's not the best way and if one did I'm sure it would take a lot of experience to do it right. For some reason I thought the new springs come wound and all you would need is the plunger. I will have to do more reseach on that if I have to get the winders, the sets are quite expensive and I read the chinese knockoffs are not durable.

But, I suppose since my interest purely lies in vintage pocket watches this is something that nearly every watch will need.

I will measure and then I'm sure I"ll be back with questions .... Thanks again!
 

Quinn

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Feb 18, 2021
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Ah Graham, I see, this is a micrometer? What is Micrometer? - FullyInstrumented

That I would need to get.

Darn them's not cheap. Allright, best not to buy the knockoff ... nice ratchet thimble on the way. Thanks Graham. The wallet's thinning seriously ;).

<FYI Graham, with your and other's guidance the disassembly of my second watch took 40 min with stopping for pictures. Not too bad, although I did make the mistake of not unwinding it and the thing exploded. Lesson learned on that. That watch is quite corroded so I'll have to try the evaporust I think. I'll do a separate thread on it when the time comes ....But disassembly and cleaning cycle went much better this time around.>
 
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gmorse

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Hi Quinn,

For some reason I thought the new springs come wound and all you would need is the plunger.
They usually do, but sometimes you have to use a spring that's longer than the ideal for the barrel, and it has to be shortened, so in those circumstances you can't just press it out of the retaining ring straight into the barrel.

But, I suppose since my interest purely lies in vintage pocket watches this is something that nearly every watch will need.
If you ever need to replace the spring in a fusee movement, bear in mind that the springs in these are wound the opposite way to going barrels, so the winder has to be able to accommodate that.

Regards,

Graham
 

Quinn

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Thanks Graham that makes sense.

I have read about the left hand vs right hand winders and some that are dual purpose. I am presuming these are clockwise.

For the Atlas, 7185052 serial, there is a mention of part 806 for the main spring. Are the specs for these parts available anywhere?

Thanks!
 

Quinn

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Feb 18, 2021
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Oops, that barrel looking pic fooled me, thanks Dave. And I found that when I look under "need a main spring it even shows the size for the main spring. Very handy!
 

Quinn

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Feb 18, 2021
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Additional question, I see a few vintage pocket watch main spring winders for decent prices, like an old K&D that comes in a wood looking round stand. It comes with 6 sizes. I tried to find out which pocket watch sizes these might fit but to no avail (realizing barrel size does not equate pocket watch size). I'm asking because a lot of my watches are 0s and 6s.
 

Quinn

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Feb 18, 2021
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Thank you so much Chris! I pulled the trigger on the winder, we'll see when it gets here to see if it's functional.
 

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