A clock with a long pendulum

I made this 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.)

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 with 72 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.)



In some of my other clocks the rims of the wheels are made from 3 mm ply, whereby the teeth are cut and the holes for the pins are drilled with a CNC router. I have made 10 clocks; the oldest still in my possession was made in 1995. Six of these clocks have grasshopper escapements and their hour hands are moved by a daisy wheel. Two have original escapments. They run for 30 hours so I spend some 5 minutes every morning winding them. This clock keeps time to within 3 seconds from day to day but drifts subject to humidity and temperature.


Wheel making techniques, illustrated
Exhibition at a clock museum
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