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Mainspring for pocket watch

Extractor

By Extractor
in Watch Repairs Help & Advice

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Extractor Member

Extractor

Posted
Posted

After having experimented with some very cheap watches I thought it was time to attempt something a little nicer. Bought this silver pocket watch and took it apart. Noticed quite a few of the jewels were shattered so is likely to be beyond my skill set at the moment to restore anyway. Despite that, I decided, probably unwisely, to examine the mainspring and measure it up for a replacement so rendering it useless in the process.

The measurement I have taken are: 

  • Height: 2.6mm
  • Thickness 0.2mm
  • Length: 520mm
  • ID of barrel: 16.5mm
  • Type TR

Then I find out there is no replacement to be found in the TR book which I accessed through the Cousins website. Am I not looking properly or have I made a big mistake in assuming a replacement could be found?

Many thanks.

IMG_20210115_184200[1].jpg

IMG_20210122_153041[1].jpg

Poljot Super WRT Addict

Poljot

Posted
Posted
19 minutes ago, Extractor said:

After having experimented with some very cheap watches I thought it was time to attempt something a little nicer. Bought this silver pocket watch and took it apart. Noticed quite a few of the jewels were shattered so is likely to be beyond my skill set at the moment to restore anyway. Despite that, I decided, probably unwisely, to examine the mainspring and measure it up for a replacement so rendering it useless in the process.

The measurement I have taken are: 

  • Height: 2.6mm
  • Thickness 0.2mm
  • Length: 520mm
  • ID of barrel: 16.5mm
  • Type TR

Then I find out there is no replacement to be found in the TR book which I accessed through the Cousins website. Am I not looking properly or have I made a big mistake in assuming a replacement could be found?

Many thanks.

IMG_20210115_184200[1].jpg

IMG_20210122_153041[1].jpg

You can never be sure that the mainspring that is currently fitted is the right one. Check what size is needed for this caliber first, or measure the depth of the barrel and subtract 0.1mm to verify is 2.6mm is right.

Extractor Member

Extractor

Posted
  • Author
Posted
23 minutes ago, Poljot said:

You can never be sure that the mainspring that is currently fitted is the right one. Check what size is needed for this caliber first, or measure the depth of the barrel and subtract 0.1mm to verify is 2.6mm is right.

Ah, that opens up quite a few more possibilities. The barrel depth is 3.4mm so it can be a considerably wider mainspring as long as I stay within 3.2mm to build in a little safety margin. You are right that the current mainspring almost certainly was not the correct one.

 

 

Poljot Super WRT Addict

Poljot

Posted
Posted
Just now, Extractor said:

Ah, that opens up quite a few more possibilities. The barrel depth is 3.4mm so it can be a considerably wider mainspring as long as I stay within 3.2mm to build in a little safety margin. You are right that the current mainspring almost certainly was not the correct one.

 

 

Exactly!

However, 3.4mm seems to be very deep, are you measuring correctly? What is the movement?

Extractor Member

Extractor

Posted
  • Author
Posted
35 minutes ago, nickelsilver said:

Cousins lists a GR 6801, 2.60 x 0.20 x 540 16.5, that would work perfectly. It has a normal "tongue end", which will work fine with the hook in your barrel.

If the exact spring cannot be found, in what order of importance would you rate the different parameters? I would have thought that the type, height and ID of the barrel are absolute requirements. Thickness and length less so?

Poljot Super WRT Addict

Poljot

Posted
Posted
7 minutes ago, Extractor said:

If the exact spring cannot be found, in what order of importance would you rate the different parameters? I would have thought that the type, height and ID of the barrel are absolute requirements. Thickness and length less so?

Strength, height, length.

Extractor Member

Extractor

Posted
  • Author
Posted

I have measured with the depth gauge of a Mitutoyo caliper, resting the the base on two sides of the curvature, allowing the depth probe to reach the bottom, keeping it as parallel as I could manage.

Poljot Super WRT Addict

Poljot

Posted
Posted
Just now, Extractor said:

I have measured with the depth gauge of a Mitutoyo caliper, resting the the base on two sides of the curvature, allowing the depth probe to reach the bottom, keeping it as parallel as I could manage.

Right, you are measuring to the top edge - do not forget that barrel lid takes some space also.

Poljot Super WRT Addict

Poljot

Posted
Posted

2.80 x .205 x 600 x 18 TR- End

GR7002TR

58 In Stock

£7.30

This is probably as good as it gets for TR end from what is available on Cousins site.

Extractor Member

Extractor

Posted
  • Author
Posted
1 hour ago, Poljot said:

2.80 x .205 x 600 x 18 TR- End

GR7002TR

Almost, but not quite. The 18 is too big as barrel ID is only 16.5mm (17mm on the reference sheet linked above so my measurement is likely to be 0.5mm off).

2 hours ago, nickelsilver said:

Cousins lists a GR 6801, 2.60 x 0.20 x 540 16.5, that would work perfectly. It has a normal "tongue end", which will work fine with the hook in your barrel.

With TR springs being difficult to find, would a DBH not work better than a normal bridle? I am thinking that the hook at least has a hole to engage in?

Poljot Super WRT Addict

Poljot

Posted
Posted
1 hour ago, Extractor said:

Almost, but not quite. The 18 is too big as barrel ID is only 16.5mm (17mm on the reference sheet linked above so my measurement is likely to be 0.5mm off).

Do not be concerned about 16.50mm Vs 17.00mm. All it means that you will not be able to push it in, but nothing stops you from using a mainspring winder, or your fingers to install the mainspring. 2.8 is way better choice than 2.6 for your deep barrel.

Extractor Member

Extractor

Posted
  • Author
Posted

I have found GR7087 which is 2.90 x .19 x 520 x 16 is stock at Cousins which is probably as close as I will get. Many thanks Poljot and Nickelsilver for your kind advice!

nickelsilver Distinguished Member

nickelsilver

Posted
Posted

The Generale Ressorts book specs the GR 7070 for this caliber, 2.90 x 0.175 x 500. Cousins has 87 in stock at a whopping 7.30 GBP. Dang, I get my springs directly from GR and they are always 25 CHF and up!

  • 3 months later...
KarlvonKoln Distinguished Member

KarlvonKoln

Posted
Posted

The Otto Frei web site carries mainsprings as well, categorized by end-type, strength/thickness, height, and length.  If you should ever have trouble getting the spring you need at Cousins (which I think would be rare) then Otto Frei is a handy back-up.

 

Daniel123 WRT Addict

Daniel123

Posted
Posted

Looks like it was made in St. Imier, excellent watch. I wouldn’t worry to much about the jewels I bet you it’ll keep good time anyway. You can change them at a later date ?

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