Tuesday, November 08, 2005

Jaeger-LeCoultre Balance Wheel

Measured the dimensions of a JLC Autotractor balance wheel the other day. Not sexy, rather perfunctory, but undoubtedly accurately made.

Ballpoint pen tip at the top
Outer diameter: 9.3 mm
Rim height: 0.60 mm
Spoke thickness: 0.20 mm
Rim width ~ 0.4 mm
Moment of inertia: ~14 mgcm2

For comparison, the Rolex 3135 movement (in the Submariner etc) balance wheel is 15 mgcm2 and the JLC 8 day balance wheel is 3.8 mgcm2.

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