Frictional rest escapement

Duplex escapement

Verified

A single escape wheel carries two sets of teeth — long locking teeth and short impulse teeth — delivering one impulse per two vibrations to a roller on the balance staff.

Schematic arrangement

How it is laid out

Outline schematic only, drawn to show the characteristic arrangement of wheel, locking member and oscillator. It is not a dimensioned working drawing and should not be used for setting up or repairing a movement.

Advantages

Excellent rate when clean and correctly adjusted
Very small energy loss

Drawbacks

Will not self-start reliably
Extremely intolerant of dirt or shock

Attribution and period

Eighteenth century; refined in England and later used in American production

Horological firsts are frequently contested. Where an invention is attributed to a named maker, that attribution is recorded as such rather than treated as settled fact.

How to recognise it

One escape wheel carrying two distinct sets of teeth: tall locking teeth and short impulse teeth (sometimes on a separate raised ring).
A roller on the balance staff with a single notch, and no pallet fork.
The balance appears to advance the wheel only on alternate vibrations.

Servicing and conservation

A duplex will stop rather than run badly, and it does not restart reliably once knocked. Any dirt in the locking teeth halts the watch. Setting up the locking and impulse relationship is specialist work; do not adjust the roller notch by trial and error.

Work on an antique escapement by a qualified watchmaker or clockmaker. Conservation of original parts is preferred to replacement wherever the object will still run.

Bibliography

Gazeley, W. J., Clock and Watch Escapements
Britten, F. J., Old Clocks and Watches and Their Makers

Duplex Escapement — Harry Leonard Nelthropp, Public domain. Wikimedia Commons file page

Duplexhemmung — Duplex Escapement — Harry Leonard Nelthropp, Public domain. Wikimedia Commons file page