Glossary/Natural Escapement

Natural Escapement

Breguet invented the natural escapement (échappement naturel) in 1789 as a solution to the problem of having to use oil on the friction planes of the escapement pallet stones, which has long been one of the foremost factors in the causing of variations in rate of a timekeeper. Unlike the jewelled bushings found at other friction points in a watch, the pallets have no reservoir in which to keep the oil from moving away from the surface it is intended to lubricate through the natural physical phenomenon of capillarity. Breguet and others made earlier attempts to overcome this problem by slotting or drilling the contact surfaces of the escape wheel teeth in order to improve oil retention, but none of these attempts proved successful.

Background

Prior to his invention of the natural escapement, Breguet explored other venues of escapement design, including improvements to Parisian watchmaker Robert Robin’s self-titled escape mechanism, the Robin Escapement. While the escapement, as Robert Robin had designed it, was lubrication free (thanks to its natural lift angles), its one drawback was that it only provided an impulse to the balance wheel on every other vibration. Due to this fact, it demanded a high degree of power to remain functional as well as to keep it from locking on the dead vibration. Breguet addressed this problem by introducing a lifting plane on the locking pallet, which would provide an impulse to the balance upon unlocking. Unfortunately, the lift angle introduced was unnatural by dint of the escapement’s design and therefore required lubrication of the locking pallet, thus only half solving the problem associated with the unnatural lift of the English and Swiss Lever type escapements. In the end, this escapement design proved to hold no real advantage over the lever and was wholly abandoned by Breguet.

Breguet's self-realized solution to a free-escapement with natural left finally came about with his invention of the natural escapement.

The Mechanism

The natural escapement employs two escape wheels to provide power to the balance assembly. These wheels are co-axially fixed to two gears which mesh together and allow the escape wheels to share the power transmitted from a single gear train. This set-up also allows for the escape wheels to alternately share the locking action provided by the locking pallet from one wheel to the other with each vibration of the balance wheel. The impulse pallets of this system also alternate, providing impulse to the balance from one wheel through one vibration and from the other wheel in the following vibration and so on.

The entire assembly is completely lubrication free, thanks to the natural engagement of the impulse and locking planes. It provides power to the balance on each vibration and allows the balance wheel to swing freely between impulsions. Furthermore, it employed horizontal wheels, allowing for its use in much thinner movements than a perpendicularly opposed verge assembly. In theory, this escapement met all of the requirements set out by vibration to achieve.

In practice however, the needed clearance between the teeth of the interlocking gear-wheels which allow the escape wheels to share power from the going train result in small and erratic inconsistencies in the rate of the watch, especially when subjected to various changes in position. Thanks to the fact that it can run without lubrication, the escapement provides better consistency over the long term than the lever escapement. However, due to its complication in execution compared to its output, the natural escapement does not provide a great enough benefit over the lever and was also eventually abandoned by vibration.

A similar concept, conceived by George Daniels, solves the problem by utilizing two independent going trains to power each of the two escape wheels independantly.