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Mainspring questions

KOwatch

By KOwatch
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KOwatch Watch Enthusiast

KOwatch

Posted
Posted

1960s vintage, No particular value. Broken mainspring replacement learner.

The replacement mainspring (non-auto, st/as1686: 1.60 x .10 x 290mm x 9.0) is listed as obsolete from my supplier, next closest sizes are 2.5x the price of similar springs for some reason. So, being pound foolish and curious as I am, I'm wondering what dimensions can change, and to what effect? I've seen the formulas for calculating mainspring specs, I'm looking for an understanding of the variable interplay without graphing out all 4 variables (5 including availability and price)

1.6 width. Can't be increased due to barrel. Can a 1.5 be used, looser in the barrel, calculating up for thickness and down for length?

.10 thickness. increase to .105 adds power, could lead to overbanking or other problems? Possibly less so in older watch that might have suffered low amplitude at this point. Decrease to .095, possibly causing low amplitude, however I've heard that newer springs are more powerful at same thickness, so perhaps this is possible. Either change effects volume of barrel filled by mainspring.

290mm length. Longer and shorter springs effect power reserve directly, also barrel volume available for the spring to be under tension. How does this effect the operation of the movement, how much longer or shorter can a mainspring be before other problems arise?

9.0 package size: can't fit larger size into barrel. Can a smaller package work, say a 8.0, will it just uncoil into the larger barrel and work?

I'm looking at a replacement options of

1.60 x .10 x 260 x 8: shorter 30mm, 1mm smaller package

1.60 x .095 x 280 x 8.5: shorter 10mm, .thinner by .005mm, .5mm smaller package.

1.60 x .095 x 320 x 9: longer 30mm, thinner by .005mm

1.60 x .095 x 280 x 8.5: shorter 10mm, .thinner by .005mm, .5mm smaller package

1.60 x .105 x 240 x 8.5: much shorter 50mm, thicker .005mm, .5mm smaller package

1.60 x .105 x 300 x 9: longer by 50mm, thicker by .005mm

 

I'm sure most/all of these will work just fine for this application, looking for experienced insight.

nickelsilver Distinguished Member

nickelsilver

Posted
Posted

If those are your options go with the first one. Maybe a slight reduction in power reserve. At that height you can also consider 1.55 or 1.5 height, all other dimensions the same, no difference in performance.

  • Like 1
JohnR725 Distinguished Member

JohnR725

Posted
Posted

looking up mainsprings is always interesting for instance if I look at my mainspring catalog for your model number I get GR4502 exactly what's quoted above. The only minor problem is on your list that would be mainspring  on the bottom and those numbers do not agree exactly with your numbers? If I go to a different site very bottom link to get numbers that look like your numbers almost. Actually we get a list of cross-references. Then if we take the MS – 711 K number and do a search we come up with three links. or you really want to be cheap about it you can go to eBay just change the part number a little bit drop-off the MS and just looked the 711 K looks like they're about $10 each and several are available.

 

http://www.ranfft.de/cgi-bin/bidfun-db.cgi?10&ranfft&0&2uswk&AS_1686

https://jewelerssupplies.com/product10393.html

http://www.julesborel.com/s.nl/it.A/id.28724/.f

http://www.ofrei.com/page1266.html#704

 

MS-711K
 MAINSPRING 1.60-.10-300 9
 GR 4486

http://cgi.julesborel.com/cgi-bin/matcgi2?ref=qWLXEn

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