Does your watch run much too fast or much to slow?
Whether new or vintage,
railroad grade
or something more common, mechanical watches rely on the period of the balance
wheel to allow the escapement to advance the mechanism at a regular pace. When a
watch is designed, and then built, a hairspring is used that will have a period
appropriate to the watch, given the mass of the balance wheel.
The most common rate of a vintage mechanical watch is 18,000 beats per hour,
although there are other rates. The watch's rate is the ideal period of the
balance wheel, which is essentially a pendulum whose period is dictated by the
length of the hairspring, and the mass of the balance. In most vintage watches,
the length of the spring can be controlled by a regulator. The regulator turns
around the center of the balance and moves two regulator pins along the
beginning stretch of the hair spring. The spring passes between the two pins.
Moving these pins makes the hairspring effectively longer or shorter and thus
changes its period.
In most watches, the full range of the regulator will not result in a change of
more than two or three minutes a day, give or take.
Mechanical watches do not have perfect rates though. If everything else is
functioning well, the intent of the regulator is to evenly distribute rate
errors, created by things like the watches physical orientation throughout the
day, or temperature changes, so that on average the watch reads well over a
period of time, such as a whole day. But it is a relatively fine adjustment.
What if a watch runs very, very fast? Like gaining a minute or more in an
hour?
A very fast rate is well beyond the range of the regulator to control. It is an
indication of a serious problem. The most common cause is dirt, oil or even
rust, on the hairspring. This can cause the spring's loops to touch as the
spring coils move in and out. One can see this happening with careful
observation of the running spring. If the coils touch, at all, this simply has
the effect of making the spring shorter, and thus faster - much shorter and much
faster. Magnetism can also cause this same problem.
A hairspring problem is the most common cause of a watch running much too fast.
There are others. For example a mainspring that is too strong can drive the
escapement too fast. The escapement may be damaged causing it to sometimes slip.
Or a wheel may be missing a tooth causing it to jump ahead as the bad spot comes
around.
What if a watch is very, very slow, such as losing minutes an hour?
Interestingly, under normal conditions where all the parts are correct, a watch
can not physically run very, very slow. Again, the period of the balance
dictates the frequency at which the escapement allows the mechanism to unwind.
The speed of motion during each instant that power is released is a small factor
in the watch's time keeping.
If a watch is behind by an hour at the end of a day, it is almost certainly
because it is actually stopping completely at some point and restarting without
being noticed. A watch might do this once for a long period, or several times
during the day. A huge array of factors play into problems causing a watch to
stop, some of them causing just slight pauses each hour, which may be hard to
notice.
The long and short of it is that vintage mechanical watches have imperfect
rates, rates which also vary slightly as they run. Small rate errors can be
accounted for, through the fine adjustment of the regulator. But larger errors
indicate a more serious trouble. A very fast watch probably has a hairspring
problem. A very slow watch is probably stopping.
You can read more about the
accuracy of vintage watches here. For other questions (and answers!) check out the
Q and A posts!
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