Text Box: HomeThe Timepiece

Escapement

 

The heart of any mechanical clock is the escapement. Without it the weights driving the clock would just hurtle towards the ground. The escapement used in the Wallingford clock is of an unusual design and it is likely that Richard was the inventor of this particular system.

 

 

 

 

 

 

Consequently the shaft attempts to turn but is restrained by a tappet (i.e. cup) engaged with one of the spokes.

 

The tappet is one of a pair mounted on a bar, the centre of which is connected to a horizontal bar above, which has weights mounted at each end.

 

In order for the spoked wheel to turn it must push the tappet out of the way; this happens slowly due to the inertia of the swinging weights above.

 

As soon as the tappet is completely clear the spoked wheel is free to rotate, which it does rapidly until the second wheel is arrested by one of its spokes engaging on the other tappet which has just moved into its path.

 
 

Two large wheels with spokes on the perimeter are mounted on the same shaft. The spokes are not in line but are offset.

 

The shaft of the spoked wheels is connected by gearwheels to the drum on which is wound the rope attached to the driving weight.

 
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


Text Box: Short clip of movementThe sequence then repeats, resulting in the spoked wheels rotating with a jerky motion at a speed determined by the size and position of the swinging weights.

 

 

 

The clock is driven by a weight attached to a rope wound around drum D.

This causes the drum to rotate in an anticlockwise direction. The drum is on the same shaft as gearwheel W72, which meshes with a pinion on a second shaft which connects to the two spoked wheels S.

 

The pinion and the spoked wheels attempt to turn clockwise but can only do so at the rate dictated by the escape mechanism. The swinging weights make one complete oscillation in 21.33 seconds. The spoked wheels make one revolution in 5 minutes 20 sec. Wheel W72 and the winding drum turn once every 48 minutes.

 

 

 

 

Text Box: One cycle of the escapement takes 21.33 seconds. There are 15 spokes, so one revolution of the spoked wheels takes 15 x 21.33 sec. = 320 sec. = 5 min. 20 sec. The pinion which meshes with Wheel W72 has 8 teeth and W72 has 72, so wheel 72 makes 8/72 = 1/9 turn for each turn of the spoked wheels. Hence W72 makes one revolution in 9 x (5min. 20 sec) which is 48 minutes, as does the winding drum.

 

 

 

 

 

 

 

 

 

At the other end of the winding drum’s shaft is a four - toothed pinion which drives Wheel W120, known as the Daywheel because it makes one revolution in 24 (mean) hours.

 

 

The shaft of the Daywheel is intended to provide the motive power for the astronomical section of the clock, although at the time of writing the two sections are not coupled together.

 

The Daywheel’s shaft is also projected forward to provide the signal for the bell to ring. When seen from the front of the clock (i.e. the bell end) this shaft turns clockwise once per 24 hours and could be used to propel an hour hand around a dial, which some people think was the case.

 

 

 

Text Box: The winding drum revolves once in 48 minutes. The 4 -toothed pinion attached meshes with the 120 teeth of the Daywheel W120. For each turn of the pinion W120 makes 4/120 = 1/30 turn. So one complete turn of the daywheel takes 30 x 48 minutes = 24 hours.

 

 

 

 

 

 

 

 

 

 

The clock is wound by attaching a handle to the squared end of a shaft carrying a pinion which meshes with a gearwheel connected to the winding drum.

 

The drum drives the clock via ratchets without which winding the clock would cause all the works to run backward.

 

 

 

 

 

 

The bell rings once at every hour.

It is powered by a separate drum with rope and weight.

 

The other components are the two spoked wheels above the escapement, the clapper arm with a weight at one end and the hammer at the other, the bell itself and a pair of tappets similar to those used in the escapement.

 

The drum attempts to turn the left hand spoked wheels anti-clockwise.

 

If the right hand spoked wheels were not fitted, then the clapper would swing rapidly backward and forward with the tappets catching the spokes of the front and rear spoked wheels alternately…

 

 

 

 

…but in fact this is prevented by one of the spokes on the right hand wheels obstructing the path of a metal block attached to the clapper arm.

 

This wheel is driven clockwise by the Daywheel’s shaft as described above.

 

The spoke scrapes along the metal block until it reaches the point where the clapper is free to move.

 

 

The clapper then starts to oscillate, but after it has struck the bell once its movement is arrested by a spoke on the other right hand wheel.

 

Text Box: Back to topText Box: HomeThe clapper must remain there until that spoke has moved on, when the process is repeated. The two right hand wheels make one revolution in 24 hours and there are twelve equally spaced spokes on each wheel, allowing the bell to be rung 24 times.