Arms of the Cathedral of St Michael and St George Anglican Compass Rose

Cathedral of St Michael and St George


The Tower Clock

As Michael Berning explains:[1] the cathedral clock was paid for by public subscription by the citizens of Grahamstown and held in trust by the trustees, namely the Grahamstown City Council. In 2011 the successors to the Grahamstown City Council namely the Makana Municipal Council decided at a regular council meeting to hand over the ownership of the clock to the Grahamstown Cathedral.[2]

Some of the teeth in the clocks escapement mechanism were damaged perhaps, some time in the 1980s. This meant the clock could no longer work mechanically. A plan was hatched by Mr Richard Grant, of the Rhodes University's Physics department to drive the clock with an electro-mechanical device. A taxi's windscreen-wiper motor that was found at a scrap yard in Port Elizabeth was coupled (by means of a rubber hose and two jubilee clips) to the input shaft of a David Brown A2 Radicon worm and wheel gearbox. The output of the Radicon box was coupled by a chain drive to a horizontal shaft on the clock mechanism that rotates at 1 revolution per hour (i.e. the minute hand speed). This horizontal shaft then transmits the drive to a vertical shaft (by means of a bevel gear of 1:1 ratio). The vertical shaft in turn drives four horizontal shafts (at 1 rev/h). The four horizontal shafts turn the four minute hands on each of the clock faces on the exterior of the tower. Four 12:1 reduction gearboxes mounted just behind each clock face take their input from the minute hand shafts and drive the hour hands. The speed of the windscreen wiper motor is regulated by a microprocessor which ensures that the minute hands rotate at precisely 1 rev/h.

The taxi's windscreen-wiper motor, gearbox and chain drive have been attached to the 1870s' clock frame in such a way that it can be easily removed without damaging the mechanical integrity of the clock (should money and skill be found one day to restore the damaged escapement mechanism).

In 1989, Grant restored the clock chimes and programmed the computer so that the clock chimed every 15 minutes - but only between 7am and 6pm, so as to not disturb the sleep of Grahamstown residents. Once the bells and frame support the bells were restored the chiming mechanism was disabled.

With a combination of old architecture and inventive modern engineering, the cathedral is the most consistently accurate clock in the CBD. One would never guess that the clock is currently running off a taxi's windscreen-wiper motor that Grant found at a scrap yard in Port Elizabeth.

Footnotes

  1. Berning, J. M. (1987) "The construction and use of Grahamstown cathedral's towers." Contree. 22(10) pp.15-22
  2. Pantsi, Nandipha. (19 April 2012)"Time Stands Still in Gtown". Grahamstown:Grocott's Mail. Accessed 2014-12-01