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The Encyclopedia of Horology

Component record · Escapement

Roller Jewel Setting

Partially verified

The seat and shellac cement holding the impulse jewel in the roller.

What it does

Retains the impulse jewel at the correct angle for unlocking and impulse.

How it works

The jewel is cemented with shellac, which is heat-softened for adjustment and holds firmly when cool.

Angle and depth in the roller determine escapement geometry.

Evolution

Unchanged in principle since the lever escapement matured.

Known variations

  • Single roller
  • Double roller with safety roller

Identification for collectors

  • A loose or tilted impulse jewel shows as erratic running and poor self-starting.

Common failure modes

  • Shellac softened by heat or solvent
  • Chipped jewel

Diagram

balance wheel with timing screwsflat or overcoil hairspringregulator index
Schematic: balance, hairspring and regulator. An outline schematic drawn to show the arrangement of the parts discussed here. It is not a dimensioned working drawing and does not depict a particular maker's calibre.

Sources & references

  1. de Carle, D., Practical Watch Repairing
  2. de Carle, D., Watch and Clock Encyclopedia
  3. Daniels, G., Watchmaking

Where sources disagree, the disagreement is stated rather than resolved silently.