The Gearless Mechanical Clock

What is the point of a gearless clock.  Surely gears are the heart and sole of any clock?  Gears require to be made with an accurate cutter and also an accurate means of dividing to obtain the correct number of teeth as well as their position.  If a way could be found to avoid using gears in making a clock, then it may be of benefit to those who do not have access to expensive machinery, or do not have the knowledge or expertise to make gears.

There is a way to produce such a  clock, and it uses a pin wheel and a ratchet wheel.  Both are relatively easy to make, and do not rely on great precision.   The teeth of ratchet wheels do not  need to be accurately formed and don't have to mesh with other wheels.  A pin wheel requires accurate dividing but the machining is a simple drilling operation.

Philip Woodward designed such a clock in 1991.  He described it in the Horological Journal and subsequently in his book 'My Own Right Time'. 

Fig. 1

The operation of the mechanism can be understood from the photograph  (Fig. 1).  On the left is the pendulum, which supports two brackets.  The upper one carries a wire gathering pawl, and the lower one a wire impulse hook.

The wire gathering pawl gathers of a tooth of the ratchet wheel in each swing.  The pendulum is such a length that the wheel turns once a minute, and so the minute hand can be attached to it.  

The pendulum is impulsed by the second wire hook, which gives impulse to the pendulum once a minute from a pin wheel which is the escape wheel.  This only happens at the completion of one rotation of the ratchet wheel when a deflector moves the impulse hook into the path of the pin wheel.   The escape wheel is prevented from rotating by a 'gated detente'.   This is only released on counter-rotation of the pin wheel just before impulse.

The escape wheel is powered by a weight which acts through a cord onto the centre shaft according to the capstan principle, and rewind is carried out by hand with a maintaining power.

The reduction gear motion work from the minute hand to the hour hand is carried out through a mechanism first described by Aaron Dodd Crane and operates on the principle of a harmonic drive or wave generator which is the subject of a separate article on this website.

The Meccano Gearless Clock has been completed but is not yet fully operational and will be described further in due course.

Michael Adler

February 2004