Goliath Pocket Watch Rebuilt OK... but now snapped main spring (!)

[Beagle2]

Hello,

I had a lot of fun rebuilding my first pocket watch, a 'Goliath' (see pic).

After 2 weeks of working well, the mainspring snapped...

I brought a new mainspring from Cousins; I would not find an exact match of the original.

• The original measured: 3.10 x 0.20 x 620 (mm)
• Cousins replacement: 3.00 x 0.23 x 640 (mm)

Could the differences in specification have caused the breakage?

Or was perhaps the spring faulty?

 

 

 

 

 

 

[vinn3]

if a main spring breaks  at one of the ends,  you can aneal the end and reshape it.  vin

[jdm]

2 hours ago, Beagle2 said:

I brought a new mainspring from Cousins; I would not find an exact match of the original.

• The original measured: 3.10 x 0.20 x 620 (mm)
• Cousins replacement: 3.00 x 0.23 x 640 (mm)

Could the differences in specification have caused the breakage?

Yes, the new MS is a lot longer and thicker, which means that will be wound more tightly, excessively stressed  and consequently it broke. As a rule of thumb the mainspring should take no more than one third of the barrel. You could probably use 3.00 x .195 x 600 x 18  (GR7194) but check for damage done by breakage.

[Beagle2]

Thanks a lot for the replies.

I think annealing / reshaping is a bit beyond me this time.

I'll try that part and see how it goes.

Thanks again

 

 

 

[rodabod]

Was the original spring blue?

[Beagle2]

Yes, it had a slight blue tinge to it. 

 

Is that an issue?

[rodabod]

14 hours ago, Beagle2 said:

Yes, it had a slight blue tinge to it. 

 

Is that an issue?

Yes, because blue steel has a different strength to modem alloy. I can’t remember the conversion factor off the top of my head. 

The length is relatively speaking much less important. 

Is the new one the snapped piece pictured? Looks like it snapped at a mid section which is surprising. 

[Beagle2]

Hello,

Yes correct, the picture is the snapped replacement spring. 

It snapped about 15 cm from the arbour hole. 

Thought it was perhaps odd, hence wondering if faulty...

 

[jdm]

1 hour ago, Beagle2 said:

Thought it was perhaps odd, hence wondering if faulty...

Why odd. You had fit a MS 15% (.23 Vs .20) thicker, and 3% ( 640 Vs 620) longer than the assumed original. That is exceeding by 18% what the manufactured had deemed safe. If the original MS was taking 33% of the barrel space, that one took 51%, that's too much.