UNLOCKING (DROP ANGLE)

In watchmaking, unlocking refers to the angle, expressed in degrees, traveled by thePallets (lever) to release the tooth of the Escape wheel from the resting plane of the Pallet stone, immediately before the Impulse begins. In the cycle of the Swiss lever escapement, the wheel tooth, held resting on the resting plane of the pallet stone (the “rest” phase, which uses the drop angle to ensure the stability of the pallets against their banking pins), must first recede very slightly to release itself from this support before being able to slide along the lift plane and transmit the impulse to the Balance. This recoil, caused by the oscillation of the balance via the plate and the impulse pin, constitutes precisely the unlocking (drop angle). Its value must be calculated as precisely as possible: too small, it compromises safety against tooth rebound; too large, it needlessly reduces the energy efficiency of the escapement and lengthens its travel. The testing of the unlocking (drop angle), the rest, and the drop (impact) — the three fundamental angular quantities of the escapement — falls under escapement-making (finishing) and is verified under the microscope during regulation / adjustment.