Anchor (Recoil) Escapement

The anchor escapement is the pendulum-clock escapement in which a pivoted part shaped vaguely like a ship's anchor alternately catches and releases the teeth of a vertical escape wheel. On each swing it gives the pendulum a small push and lets the wheel train advance by a fixed amount, moving the hands forward.

The escape wheel has pointed, saw-like teeth slanted backward against its direction of rotation. Curved faces on the two arms of the anchor, called pallets, receive the teeth. The anchor's central shaft, the crutch, ends in a fork that embraces the pendulum rod, and the pendulum hangs from a short suspension spring directly behind the anchor, with the anchor's pivot aligned to the bending point of the spring. After a tooth drops onto a pallet, the pendulum's momentum keeps moving that pallet inward, pushing the escape wheel backward for a short distance until the swing reverses. This backward movement is the recoil that gives the escapement its other name.

Recoil briefly reverses the whole wheel train on every tick, causing extra wear and inaccuracy; the backward slant of the teeth and slightly convex pallets keep the tooth points from digging in. Neither the anchor nor its deadbeat refinement is self-starting, so the pendulum must be set swinging. In late nineteenth-century British practice the pallets were usually set 90 degrees apart, and a longcase clock with a seconds pendulum often had a 30-tooth escape wheel turning once a minute so that the seconds hand could sit on its arbor.