Need to find a mainspring

[meep1999]

I need help finding a certain mainspring for an old pocket watch I have. The dimensions are: Length=520mm, Height=2.4mm, Strength=0.22mm, Inner barrel diameter= 15.5mm. It uses a normal bridal hook

[clockboy]

I have had a look at my GR catalogue & the following are the nearest I could find:

 

GR 6576    H 2.40     S 0.20     L 520    Dia. 16

GR 6577    H 2.40     S 0.20     L 540    Dia. 16.5

GR 6596    H 2.40     S 0.22     L 520    Dia. 17

Cousins may be your best bet. I have looked in their catalogue & they have in stock.

GR 6578    H 2.40     S 0.20     L 560    Dia. 17

If too long give them call.

 

[szbalogh]

I would repair it

 

[ftwizard]

7 hours ago, szbalogh said:

I would repair it

 

Care to elaborate?

[Cad101]

You could try riveting it in 2 places you would need a donor peice of spring tho you then drill a hole either side of the break and rivet the backing strip on with a brass rivets not the best solution as your break is very near the end where it curves alot your probably better of trying to find a replacement although you wouldnt loose anything by trying to mend it as its alreadt broke.

[StuartBaker104]

You could theoretically repair that spring by letting down the temper on the inner coil and punching a new hole in it. However it is most likely that the rest of the spring is at the end of its useful life.

You should ask yourself the question of what is the "correct" spring for this watch, rather than trying to match what you found. Just as today you can't easily buy every permutation, it will have been that way in the past and the nearest available will have been used. If this watch has had 3 or 4 mainsprings in its life then you could find the one fitted is far from ideal. I would refer to the calculators on this page: http://www.vintagewatchstraps.com/blogmainsprings.php

Assuming that your barrel arbor is 1/3 the diameter of the barrel, then your old spring would only have been able to fit 5 winding turns. Assuming you have a going barrel, not a fusee, then ideally you would have room for 6 1/2 turns, which should give you 35 to 40 hours running.

The calculators on the above page suggest that you should have a spring which is 0.19 thick and 480mm long. Cousins has GR6561 which is 0.19 x 500.

A spring which is too strong (thick) will cause the escapement to bank whereas one too weak will cause a low amplitude which may affect accuracy. Strength is a factor of the cube of the thickness so a small change will have a large effect, but personally on an old watch I would err on the weaker side.

Stuart

[clockboy]

8 hours ago, StuartBaker104 said:

You could theoretically repair that spring by letting down the temper on the inner coil and punching a new hole in it. However it is most likely that the rest of the spring is at the end of its useful life.

You should ask yourself the question of what is the "correct" spring for this watch, rather than trying to match what you found. Just as today you can't easily buy every permutation, it will have been that way in the past and the nearest available will have been used. If this watch has had 3 or 4 mainsprings in its life then you could find the one fitted is far from ideal. I would refer to the calculators on this page: http://www.vintagewatchstraps.com/blogmainsprings.php

Assuming that your barrel arbor is 1/3 the diameter of the barrel, then your old spring would only have been able to fit 5 winding turns. Assuming you have a going barrel, not a fusee, then ideally you would have room for 6 1/2 turns, which should give you 35 to 40 hours running.

The calculators on the above page suggest that you should have a spring which is 0.19 thick and 480mm long. Cousins has GR6561 which is 0.19 x 500.

A spring which is too strong (thick) will cause the escapement to bank whereas one too weak will cause a low amplitude which may affect accuracy. Strength is a factor of the cube of the thickness so a small change will have a large effect, but personally on an old watch I would err on the weaker side.

Stuart

Excellent advise. With vintage watches it is not always possible to get exact replacements.For me repairing the spring would be a very last resort.