How it works Anchor escapement

1 how works

1.1 recoil
1.2 crutch , fork
1.3 design details

how works

the anchor escapement consists of 2 parts: escape wheel, vertical wheel pointed teeth on rather saw teeth, , anchor, shaped vaguely ship s anchor, swings , forth on pivot above escape wheel. on 2 arms of anchor curved , flat faces teeth of escape wheel push against, called pallets. central shaft of anchor attached fork pushed pendulum, anchor swings , forth, pallets alternately catching , releasing escape wheel tooth on each side.

each time 1 pallet moves away escape wheel, releasing tooth, wheel turns , tooth on other side catches on other pallet, moving toward wheel. momentum of pendulum continues move second pallet toward wheel, pushing escape wheel backwards distance, until pendulum reverses direction , pallet begins move away wheel, tooth sliding along surface, pushing it. tooth slides off end of pallet, beginning cycle again.

neither anchor escapement nor deadbeat form, below, self-starting. pendulum must given swing them going.

pendulum , anchor escapement.

(a) pendulum rod

(b) pendulum bob

(c) rate adjustment nut

(d) suspension spring

(e) crutch

(f) fork

(g) escape wheel

(h) anchor


recoil

the backward motion of escape wheel during part of cycle, called recoil, 1 of disadvantages of anchor escapement. results in temporary reversal of entire wheel train driving weight each tick of clock, causing wear in wheel train, excessive wear gear teeth, , inaccuracy. can cause points of escape wheel teeth dig pallet surface. teeth slanted backward, opposite direction of rotation, , surface of pallets convex, prevent this.

another reason escape wheel teeth slanted backward safety measure. if clock moved without immobilising pendulum, uncontrolled swinging of pendulum can cause anchor pallets collide violently escape wheel. slanted teeth ensure flat faces of anchor pallets hit sides of teeth first, protecting delicate points being broken.

the deadbeat escapement (below) doesn t have recoil. 1 way determine whether antique pendulum clock has anchor or deadbeat escapement observe second hand. if moves backward after every tick, showing recoil, clock has anchor escapement.

crutch , fork

the shaft of anchor, called crutch ends in fork embraces shaft of pendulum, giving transverse impulses. pendulum rod hung short straight suspension spring attached sturdy support directly behind anchor. pivot of anchor aligned bending point of spring. arrangement results in more stable pendulum support suspending pendulum directly anchor.

design details

the anchor tolerant of variations in geometry, shape varied widely. in late 19th century, in britain, usual design 90° angle between pallets, meant locating anchor pivot distance of √2 ≈ 1.4 times escape wheel radius escape wheel pivot. in grandfather clock, had pendulum swung once per second, escape wheel had 30 teeth, made escape wheel rotate once per minute second hand attached shaft. in 30 tooth escape wheel pallets span 7½ teeth. impulse angle of pallets, determined swing of pendulum, 3°-4°.