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Congreve Rolling Ball Clock

Although Sir William Congreve patented this clock design in 1808, other clocks adopting similar principles already existed, including one built in 1804 by Robert Gryson displayed in the National Museum of Scotland.

Some engineers have built replicas from scratch using original plans but similar designs following the same principle have been produced in greater numbers by several small firms over the past fifty years or so, some (like Devon Clocks) even producing kits for home assembly. The most common now is a miniature version made in China (Image 1), which is poorly made, poorly assembled and poorly finished. It's so unreliable and difficult to set upi that I have produced my own set of instructions that you're welcome to try:

First, ensure the display surface is level, solid and horizontal. It can be made to work if the surface isn’t quite perfect but it just takes more effort. Now you can throw away the spirit level; it causes more problems than it solves because the machining tolerances and assembly variations on these clocks are huge!

Now check that the zig-zag track is tight on its centre mount and sitting parallel with the base (not skewed). If it’s not straight and tight you will need to remove the movement to gain access to the two small screws that secure the track to the mount: undo the 4 finials and remove the bottom screw in the tilt rod attached to the back of the track. When refitting the movement and rod make sure that the two control levers engage in the slots in the track ends (see Image 4). Tighten the lock nut at the top of the tilt rod.

Now you need to level the clock base in two planes using the three screw in feet (Image 2) but don’t use a spirit level. Wind up both barrels, place the ball on the track at the front and give it a push start; gravity does the rest:

If the ball rolls to the back faster than towards the front, you need to extend the centre foot at the back by turning the foot clockwise (viewed from above). Alternatively, retract the left and right feet at the front (counter-clockwise). It’s best done by watching and listening; the travel is too short for a stopwatch. Once the ball is moving forwards and backwards at equal speed, you can move on to the next stage.

If the ball reaches the left faster than it does to the right, you need to extend the left front (or retract the right foot); you might also need to make a much smaller adjustment to the rear foot in the same direction. A stopwatch here is useful but not essential; it is designed to take 12 seconds each way but for the moment, just make sure both directions are approximately equal.

If the ball jumps off when the track reverses direction, the zig-zag track is too steep. To reduce the angle, stop the plate when it is down on the right and then turn (in a clockwise direction) the small screw on the escapement at the back (Image 3)– the part that the tilt rod is attached to, which rotates 180 degrees every time the track plate reverses. The thread on this adjuster is far too coarse to adjust the plate accurately so keep making very small adjustments until the ball reverses on the track reliably.   

If the ball stops at the end of the track instead of reversing, there are 3 possible causes apart from dirt:

The track plate angle might just be too shallow so increase it by means of the adjuster described in 7 above. You may notice that the zigzag groove changes angle for the final sweep at each end; this effectively increases the angle of attack and so increases the speed of the ball to help it strike the vertical control lever more vigorously.

The vertical control levers (Image 4) that pass through the slots at each side of the track plate might be misaligned and need gently bending. They must sit in the centre of the slot so that there is no binding on any side of the hole. They must not be too close to the front or back of the slot and be sure to check both, not just the one that appears to be the problem as they are both attached to the same link rod at the back so each one affects the performance of the other. This is why in 3 above I advised checking that the plate was firmly and squarely attached by the two centre screws; if it wobbles, the clock will fail.

The ball may not be releasing the lever because the adjuster on the link rod at the back on the left (Image 5) is wrongly set. The adjuster is simply a tiny brass counterweight projecting backwards; the further out it is the less sensitive is the control lever to the ball’s impact so turn it inwards.

Timekeeping is truly dreadful; if you can get it to within a few minutes a day, you've equalled my best! The only way to regulate it is to adjust the angle of the track plate; the steeper it is the faster the ball will travel but this comes at the risk of the ball leaving the plate altogether so be prepared to compromise.... a lot. There are the usual obstacles to accuracy such as temperature fluctuations causing expansion and contraction but more uniquely, any dust on the zigzag track produces timing variations. However, the biggest problem is the time it takes for the ball to change direction; it’s just not consistent every time.

Adjusting a Congreve

  • An inexpensive Chinese Congreve rolling ball clock
  • The Congreve rolling ball clock has three adjustable feet for levelling during setup
  • The Congreve rolling ball clock has an adjustable escapement at the back to increase and decrease the angle of the track plate
  • The Congreve rolling ball clock's track plate is controlled by two vertical levers, one at each side
  • The sensitivity of the Congreve rolling ball clock's tilt levers is made by way of a counterweight at the rear