Pocket Watch mainspring

[MattJ]

I've a Swiss pocket watch, no markings to identify the movement, but it needs a new mainspring.

The old mainspring is 1.9mm wide, 0.185 thick and 620mm long. The barrel is 19mm and the arbor is 4.8mm so a length calculator says 590 to 737mm, so the 620mm is about right.

The mainspring has a hole end, so that seems to make it difficult to find.

I've found a reference that says this matches a Baumgartner/BFG 760 or 80 calibre, or GR5630, but not found anywhere that stocks anything that matches or even seems to be close to this mainspring, particularly with a hole end.

Are there sources who aren't on Internet?

Thanks in advance for any advice

Matt

[oldhippy]

 Have you looked at this list which we provide on this forum. Here is the link.

https://www.watchrepairtalk.com/links/watch-clock-repair-suppliers/

 

[jdrichard]

Go to CousinsUK and then generic mainsprings and you can select based on dimensions and barrel size: and end type. Do it all the time.


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[StuartBaker104]

Matt,

If Cousins doesn’t have it, then you could spend a few years waiting for the right size NOS spring to come up on eBay only to discover it is set or rusty. There are other places on the net, but much harder to search their stock.

I tried checking Cousins for all 1.9mm hole end springs, and you only get one hit which is way too long. I have seen standard bridle end springs in a barrel made for a hole end spring, but not my recommendation!

First of all, where did you go to check the spring you found in the watch is the correct size? You need a spring which gives 0.1 to 0.2mm clearance on height - so check your barrel depth, and I like the reverse engineering calculator here http://www.vintagewatchstraps.com/mainsprings.php#reverse to work out thickness and length. If you have a 19mm barrel i/d, then you do probably need a thicker spring - more like 0.24mm. Read the whole page for more info.

You may have to buy a longer spring and cut to size and create your own hole. Mainspring hole punches come up on eBay from time to time, but see below on how to create a hole without...

Here is the reference on “heat the end as before and make the hole”

The chamfer tool described is a bit like a centre punch with a pyramid shaped end.

[MattJ]

Thanks all. 

@oldhippy - thanks for the list of suppliers, I will work my way through them.

@jdrichard - I have tried Cousins and they have very few with hole ends.

@StuartBaker104 - thanks for the calculator, I'll see if the parameters it provides match any of the off-the-shelf springs. Otherwise I may have to, as you say, modify an off the shelf spring to fit - I have Donald De Carle's excellent book, but thanks for the images.

[jdrichard]

I think you can actually simply drill a hole in a mainspring these days??


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[jdrichard]

Matt,
If Cousins doesn’t have it, then you could spend a few years waiting for the right size NOS spring to come up on eBay only to discover it is set or rusty. There are other places on the net, but much harder to search their stock.
I tried checking Cousins for all 1.9mm hole end springs, and you only get one hit which is way too long. I have seen standard bridle end springs in a barrel made for a hole end spring, but not my recommendation!
First of all, where did you go to check the spring you found in the watch is the correct size? You need a spring which gives 0.1 to 0.2mm clearance on height - so check your barrel depth, and I like the reverse engineering calculator here http://www.vintagewatchstraps.com/mainsprings.php#reverse to work out thickness and length. If you have a 19mm barrel i/d, then you do probably need a thicker spring - more like 0.24mm. Read the whole page for more info.
You may have to buy a longer spring and cut to size and create your own hole. Mainspring hole punches come up on eBay from time to time, but see below on how to create a hole without...

Here is the reference on “heat the end as before and make the hole”

The chamfer tool described is a bit like a centre punch with a pyramid shaped end.

Great file btw


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[StuartBaker104]

20 hours ago, jdrichard said:

I think you can actually simply drill a hole in a mainspring these days??


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Probably! But where’s the fun in that?!