Why do wind-up watches occasionally speed up?
luna-sea Wed 03/12/08 11:16
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To keep perfect time the mainspring of the watch has to have the same tension throughout its length. A slight variation ie too tight or too loose or perhaps temperature
could affect the accuracy
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Pardon my ignorance,davidicus, but surely it is the escapement that doles out the time, the mainspring being merely the source of power for moving the hands.
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Not quite, Chakka. If more spring pressure is applied, the escapement moves faster. Less pressure, it moves more slowly. You can observe this by using your finger to increase or decrease the rotation on a watch's gearwheel that drives the escapement.
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But.... isn't pressure with the finger outside the parameters of the watch's design? If it was the spring, the watch would go faster when first wound up and slow down at the end of the recoil.
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You're right, Wildwood, and this was, and still is, a problem with windup watches. Various solutions have been tried, but none are totally satisfactory. The best solution is probably the 'automatic' self-wind mechanism, which can provide a near constantly fully-wound mainspring . Read more here.
Note how most watches run for longer than their stated time-between-windings. This is because after the stated time, the mainspring is entering its lower torque range with less reliable timekeeping.
Further to the question... If a clockspring is shortened, then when it's wound up, its output force is increased. If the mainspring in a watch is corroded, or has rough bits, or is dirty, the coils can stick together when it unwinds. This produces the same effect as if the spring were shortened - the spring force is increased and the escapement can run faster.
So, Luna-sea, if your watch occasionally runs faster, it either needs cleaning, or a new mainspring.
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Question Author
Thanks everyone for all your answers and particularly to heathfield for the possible instruction to get my watch cleaned.
It is a Seiko-automatic winder, by the way.
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Question Author
Sorry-should have read;
the instruction for my watch to possibly need cleaning.
:0)
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I bow to the obviously greater knowledge of others. I learn something every day thanks to AB.
What watch is it, luna-sea? Mine is also a Seiko self-wind which I have had for decades - a Bell-matic, which charmingly uses the case as the gong of its alarm.
I have had it cleaned and overhauled only once during that time and it works very well indeed.
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Question Author
It must be nearly twenty years old chakka.
A Seiko 5 Automatic.
It cost me about £30 and is extremely reliable apart from the odd speeding up now and then but cannot fault it in any other way.
I see Kinetic watches now in the shops at ten times the price I paid for mine.
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Lucky us, luna-sea. Cheers.
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