[time-nuts] Watch Real or Fake?

[Chuck Harris]

Hi Brooke,

Back before the development of Elinvar, Metelinvar, and Nivarox hairsprings,
and Glucydur balance wheels, watches used to need temperature compensated balance
wheels.  The temperature compensation principally compensated for the temperature
variations in the springiness of the hairspring.  It also compensated for the tendency
of the balance wheel to grow and shrink in diameter with temperature.  The rim of a
compensated balance wheel was made of a bimetalic construction, and was cut so that each
half of the rim was attached only to one arm of the hub.  As temperature varied, the
bimetallic rim would expand and contract, thus changing the rate of the watch.  The
hope was that the change in the wheel diameter would exactly match the change in the
hairspring (with temperature), and the watch would keep good time.  It is terribly
difficult to get these two changes to match in way where they cancel each other out.

With the advent of Elinvar, Metelinvar, Nivarox, and other alloys of Invar used in
hairsprings such compensation is no longer needed, or desirable.

Pretty much any quality watch made since the 1960's will have some variant of an
Elinvar hairspring, and a Glucydur balance wheel.

The screw weights on the rim of the balance wheel serve a double purpose.  First,
they make sure that the wheel balanced so that there is no heavy side of the wheel,
and second, they are used to adjust the mass of the rim of the wheel to exactly
match the spring constant of the hair spring so that the wheel will resonate at
exactly the correct rate.

I would say that given the age of the watch, the balance construction seems
appropriate.

-Chuck Harris


Brooke Clarke wrote:
> ); SAEximRunCond expanded to false
> Errors-To: time-nuts-bounces+cfharris=erols.com+cfharris=erols.com at febo.com
> 
> Hi:
> 
> I got this watch on eBay from Russia.  After making the photo for it's web page 
> I could see that the balance wheel appears to be all brass and is not cut like 
> would be done with a bi-metal balance wheel.
> 
> So now am thinking it's a fake.  If you know watches have a look:
> http://www.prc68.com/I/Watch-Real-Fake.shtml
> 
> It's harder to see a very similar watch on eBay now at:
> http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=250138676169
> With the watch running you can't tell if there's the cuts in the balance wheel.
>