A clock with a long pendulum

I made this 30 hour clock in 1997 with simple hand tools and an electric drill with a drill stand.
The pendulum is about 250cm long and makes one swing every one and a half seconds.
(Effective length from suspension to CG: 223.6 cm.)
It keeps reasonable time for a clock with a wooden pendulum, a couple of seconds a day.

clock with a long pendulum

Grasshopper escapement
Pallets positioned by spiral springs, just visible.

Escape wheel
5 spokes, 1 rev. in 5 mins.
100 pins, 0.6mm ∅

Escape wheel rim
5mm cross-grain balsa
sandwiched between
two layers of 1 mm ply.

Pinion
six 3mm ∅ pins each
with a 4 mm brass sleeve.
Sleeves are free to rotate.

Hour wheel teeth
each 5 x 5 x 17 mm,
sanded to involute curve.
and sandwiched between
two layers of 1 mm ply.

Hubs
12 x 1 mm brass tube
two 10mm ball-bearings
on 5 mm steel axles.

Hour hand is turned by a daisy wheel.

Pendulum
varnished spruce.

Pendulum weight:
steel tube, 35cm long
4.5cm outside diam.
The pendulum is connected to the clock by a length of piano wire. It is ground down thin to form a flexible hinge where it meets the pendulum and is attached to the pendulum crutch with a ball- bearing. The photo shows about 1 metre of the pendulum, 2/5 of its total length. The connecting wire is exactly halfway up.


clock with a long pendulum

Variations

When this clock was shown at the University of Tokyo in 2007 it ran very slow so I had to raise the weight of the pendulum by about 5mm. I believe this was because of the reduced gravity in Tokyo (35.6°N) compared to Berlin (52,5°N).
According to the World Gravity Network map,
Potsdam: 981.274 Gals, Kyoto: 979.72 Gals.

I also showed it in a exhibition in Burg Eisenhardt, a castle in the Mark Brandenburg, which has high ceilings. I took the opportunity of making a two second pendulum - about four metres long. (Since it ticked slower I had to make a new escape wheel: with 75 pins instead of 100.)



The teeth and spokes of the wheels are made of wood strip and the rims are made of thin plywood and balsa. In some clocks the teeth are cut from 3 mm ply with a CNC router. I have made 8 clocks like this; the oldest still in my possession was made in 1995. It has been running continuously, and keeps time to within 2 or 3 seconds from day to day but drifts subject to humidity and temperature. Six of these clocks have have grasshopper escapements and their hour hands are moved by a daisy wheel. Two have original escapments.

If you are making a clock in this style, contact me and we can compare notes.

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Wheel making techniques, illustrated
Exhibition at a clock museum
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