Anchor Escapement - Disadvantages

Disadvantages

The anchor escapement is reliable and tolerant of large geometrical errors in its construction, but its operation is similar to the old verge escapement, and retains two of the major disadvantages of the verge:

• It is a frictional escapement; the pendulum is always being pushed by an escape wheel tooth throughout its cycle, and never allowed to swing freely. This makes the clock's rate sensitive to changes in the drive force, a problem called lack of isochronism. Any small changes in the force applied to the pallets, by a change in lubrication or the declining force of the clock's mainspring as it runs down for example, will change the period of the pendulum's swing. Anchor clocks driven by a mainspring slowed down slightly as the mainspring unwound, and required a fusee to even out the force of the mainspring to be accurate.
• It is a recoil escapement as mentioned above; the momentum of the pendulum pushes the escape wheel backward during part of the cycle. This causes extra wear to the movement, and the backlash of the gear train applies varying force to the pendulum, causing inaccuracy.