"Escapement, the mechanism fitted between the train and the regulating organ of most timepieces. The purpose of the escapement is to maintain the oscillations of the regulating organ, i. e. the balance or pendulum." (Berner)
"A mechanism that is fitted between the gears and the regulating organ. Its function is to suspend the gears' motion at regular intervals and to supply energy to the balance." (FHH)
Types of escapement
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Co-axial
The Co-Axial escapement has 3 pallet jewels in the lever transferring energy to drive the balance, instead of the traditional 2. The element that differentiates this escapement from traditional levers is the lack of sliding impulse — replacing the impulse to the balance wheel by a pushing action rendering lubrication unnecessary. Identical in concept to the earlier Breguet Echappement Naturel.
Cylinder
The cylinder escape was invented by George Graham about 1720 influenced by a prior version developed by Thomas Tompion in 1695. The escape-wheel would drive a partially cut away cylinder built into the balance assembly, giving impulse and momentum to the balance wheel. The cylinders were generally made in steel and polished but high quality versions were also made in ruby by Breguet. The escapement was a "frictional-rest" design, meaning there is always contact between the escape wheel and the cylinder/balance.
Breguet Subscription pocket watch ruby cylinder and steel escape wheel.
Breguet Subscription pocket watch ruby cylinder.
Breguet Subscription pocket watch ruby cylinder movement.
Detent
The (spring or pivoted) detent escapement was traditionally used in marine chronometers. Provides impulse to the balance in one direction and is not self-starting but, generally very accurate due to the significantly reduced friction developed by the functioning of the escapement.
Duplex
A frictional rest escapement with two layers of teeth on the escape wheel.
English lever
The English lever funtions in a similar fashion to the Swiss escapement. In a Swiss lever the escape wheel, balance and lever are in a straight line. In an English lever they form a 90 degree angle and the escape wheel is located under the balance wheel, unlike the Swiss counterpart. The design of the escape wheel teeth are "ponied" apposed to clubbed.
Pin pallet
The pin pallet escapement is similar in approach to the lever escapement, but was used a cheaper alternative in watches and clocks. Replacing horizontal pallet jewels on the lever with vertical metal (occasionally ruby) pins. The form of the escape wheel teeth is also modified.
Swiss lever
The Swiss lever escapement, is the most commonly used in mechanical watches. The lever, also named "anchor" because of its shape, transmits energy from the mainspring via a train of wheels to the balance in order for it to oscillate. Providing impulse in both directions the balance oscillates through, and between impulses locking the train so that the mainspring unwinds at a consistent rate.
Breguet Classique Chronographe 5287 Swiss lever.
Breguet Classique Chronographe 5287 Swiss lever & escape wheel.
Jules Jurgensen Swiss lever with counter poise balance weight. (Antique)
Verge
One of the earliest forms of escapements used in pocket watches originating from early turret clocks. Crude by today’s standards but important in the place it holds in the history of development of mechanical time keeping.
Assembled verge movement showing contrate wheel which powers crown wheel.
The verge staff with its two pallets which come in contact with the crown wheel teeth.
The crown wheel which drives the balance wheel through contact with the verge staff pallets.
Associated Terms
Banking, a term used describing the limiting movement of a lever/anchor. The lever banks/rests against banking pins or inner section of the lever bridge or cock.
Beat, alternating motion: the beat of a pendulum. Noise caused by a shock produced by alternating motion. This watch has an irregular beat: the sounds made by the escapement recur at irregular intervals. (Berner)
Guard pin, found on the lever escapement, a small metal pin which prevents the ancre from desynchronising with the balance wheel.
Horn, horn-shaped extremity of the Swiss ancre, the outside of the section that received the impulse jewel.
Impulse, transmission of power from the mainspring through to the escapement.
Impulse jewel, the semi circular jewel fixed to the balance wheel assembly that transmits power to the balance to make it oscillate.
Pallets, parts of the escapement of a watch normally made from synthetic ruby which engage with the escapement wheel.
Safety, "In horology, precautionary measure taken to prevent stoppage or incorrect functioning. In an escapement, the draw and run to the banking are safeties." (Berner)
Safety pin, see above -guard pin-
Shellac, "Resin used by watchmakers as a cement. The parts to be cemented are put on to a holder, sprinkled with shellac and heated. The shellac hardens as it cools. Shellac dissolves in methylated spirit." (Berner)
Unlocking, In a Swiss or English lever escapement, the term unlocking is the angle through which the lever moves to unlock the escape-wheel in order for impulse to then be given to the balance wheel.