Lever escapement

An escapement is a mechanical linkage that delivers impulses to the timepiece's balance wheel, keeping it oscillating back and forth, and with each swing of the balance wheel allows the timepiece's gear train to advance a fixed amount, thus moving the hands forward at a steady rate.

The lever escapement was invented by British clockmaker Thomas Mudge around 1754,[1][2] and improved by Abraham-Louis Breguet (1787), Peter Litherland (1791), and Edward Massey (1800).

[1][2] Since about 1900 virtually every mechanical watch, alarm clock and other portable timepiece has used the lever escapement.

The escape wheel has specially shaped teeth of either ratchet or club form, which interact with the two jewels called the entrance and exit pallets.

Once the entrance tooth leaves the impulse plane of the entrance pallet, the wheel is able to turn a small amount (called the drop) until the exit tooth of the escape wheel lands on the locking face of the exit pallet.

From the release from the entrance pallet to this point, the escape wheel will have turned through exactly one half of the 24-degree angle between two teeth.

After the exit tooth locks, the balance wheel rotates anti-clockwise, free of interference from the escapement until the hairspring pulls it back clockwise, and the impulse pin re-enters the fork.

The balance wheel continues clockwise, again free from interference until it is pulled back by the hairspring to the center position.

The draw holds the lever against the banking pins during the detached portion of the operating cycle.

A cheaper, less accurate version of the lever escapement is used in alarm clocks, kitchen timers, mantel clocks and, until the late 1970s, cheap watches, called the Roskopf, pin-lever, or pin-pallet escapement after Georges Frederic Roskopf, who mass produced it from 1867.

The oil eventually thickens, causing inaccuracy, and requiring cleaning and reoiling of the movement about every 4 years.

is to make the escape wheel and other parts out of harder materials than steel, eliminating the need for lubrication.

Ulysse Nardin in 2001, Patek Philippe in 2005, and Zenith in 2013 introduced watches with silicon escape wheels.

Inline or Swiss lever escapement (blue) and balance wheel (yellow)
Animation of inline lever escapement, showing motion of the lever (blue) , pallets (red) , and escape wheel (yellow)
A lever escapement in a mechanical watch. The largest brass circle is the balance wheel. The escape wheel is the silver gear above and to the right of it whose bearing is surrounded by decorative engraving. Most of the lever itself is hidden, but both pallets are visible.