It should not be any different to the shortening and lengthening though, my
guess is that the clock is not very accurate as it has worn parts dirt or no
lubrication, but do be careful with the latter, its quite a specialist
subject cleaning and lubricating a clock.

Is it one which is operated by clockwork or the weight driven kind, the
latter can be very temperamental.
Brian

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The Sofa of Brian Gaff...

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"Chris Hogg" wrote in message
...
On Thu, 20 Aug 2020 12:23:02 +0100, "NY" wrote:

I have a granddaughter clock and I'm having great difficulty adjusting it
so
it keeps good time. The pendulum bob (a metal disc) sits loosely on a
threaded rod which has lugs allowing it to sit on the oscillating part of
the clock mechanism. The bob rests on an adjustable nut on the rod, which
allows the pendulum to be lengthened or shortened.

It used to lose about 5 minutes a day, but I've progressively wound up the
nut 1/2 turn at a time, to shorten the pendulum so it has a shorter
period.
I'd got it almost right, but then I went backwards: a further shortening
made it run *slower*. I wound the nut a full turn shorter which was
evidently too far (the clock ran too quickly), but when I backed it off
1/4
turn, it started to run a lot slower than before I originally adjusted it.

Part of the problem is that it is necessary to turn the clock round to get
at the back, and then unhook the pendulum from its mount on the mechanism
to
be able to get at the adjustment screw. I'm wondering whether it doesn't
always reseat to the same position and/or slight differences in how the
clock sits on the floor are making things non-reproducible.

The floor is modern hardwood tiles laid on a concrete floor that was
levelled with self-levelling compound when we had building work last year,
so it's not the problem of a sloping floor or a carpet that is thicker
near
the walls than a few inches into the room.

Any suggestions?

Time-keeping of the clock in the Elizabeth Tower (aka and wrongly
called 'Big Ben') is done by adding or subtracting weights (old
pennies etc) to the main pendulum weight. In principle, the period of
a pendulum is independent of the mass of the bob, but by adding or
subtracting pennies they shift the C of G slightly, altering the
effective length of the pendulum.
https://www.careline.co.uk/wp-conten...5/p040d4h0.jpg
Perhaps you could try something similar: little pieces of solder wire
wrapped around the rod just above the bob, for example.

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Chris