Re: Temperature compensating a pendulum clock?
- From: jeff_wisnia <jwisniaDumpThisPart@xxxxxxxxxxxxxx>
- Date: Fri, 13 Jan 2012 15:28:35 -0500
On 13/01/12 07:23, jeff_wisnia wrote:
We have a very nice pendulum wall clock in our kitchen which has the
type of movement where a battery powered electric motor winds the spring
of a traditional type pendulum movement.
The clock keeps excellent time in the summer, but during the cold months
of our New England weather, when we let the temperature in the part of
the haouse where the clock is located drop into the 50s during the
night, the clock gains about 3 minutes a day.
I presume this is due to the pendulum shaft shortening with temperature
and I can sort of compensate for it by adjusting the bob downwards a
bit, but it's still not accurate enough to suit my taste.
what is the pendulum rod made of?
the other thing to consider is the suspension spring in cold temps will stiffen the spring and make the rate faster,
I was wondering if I could fasten one end of a strip of bimetal
scavengened from an old thermostat onto the back of the bob in such a
way that the free end moved downward as the temperature dropped and with
some trial and error tuning end up with a "temperature compensated
hmm I think you find will that won't make much of difference, better to improve the pendulum, if for example it's a brass rod brass/lead bob, then simply fitting a steel rod will help or a timber one, if you could get your hands on it invar would make a better rod as it won't vary much in length.
If I decide to take on the challenge (Just for Ss & Gs) I'll keep my eye open for a glass rod of the right length and shape. I know the thermal coefficient of glass is quite low. I should be able to replace most of the length of the pendulum rod with a glass rod with epoxied on metal ends, maybe then sprayed with bronze paint so it doesn't look so odd.
It's been a while since I've mucked around much with clocks, the most interesting one I did about 45 years ago had a "verge" escapement. It's still hanging on a wall in our home but don't even think about asking me how good a timekeeper it is. <G>
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.8*10e12 furlongs per fortnight.
Comments appreciated, I'd really like to keep the existing movement in
that clock rather than jump to a quartz movement.
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