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Accurate Clock Pendulums$
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Robert J. Matthys

Print publication date: 2004

Print ISBN-13: 9780198529712

Published to Oxford Scholarship Online: January 2010

DOI: 10.1093/acprof:oso/9780198529712.001.0001

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Rate adjustment mechanisms

Rate adjustment mechanisms

Chapter:
(p.91) Chapter 14 Rate adjustment mechanisms
Source:
Accurate Clock Pendulums
Author(s):

Robert James Matthys

Publisher:
Oxford University Press
DOI:10.1093/acprof:oso/9780198529712.003.0014

The usual coarse adjustment for trimming a pendulum's clock rate is a threaded nut beneath the bob, which moves the whole bob up and down the pendulum rod. The surface of the thread is somewhat rough, particularly if the material is invar, which machines poorly. The thread's roughness prevents any sort of smooth adjustment. Axially, 0.001 inch equals 1 second per day on a pendulum with a 2-second period. To get an adjustment sensitivity of 1 second per day, the thread must be lapped, or more correctly, rubbed smooth. And if the thread is not smooth, the whole bob weight will rest on the small raised points of the rough thread's two facing surfaces, creating high stress points and a potentially unstable joint (at the micro-inch level). Using a sleeve bushing or a thick washer of predetermined length underneath the bob as a coarse rate adjustment, and a small threaded nut at the top of the pendulum rod as a fine rate adjustment provide a better way to trim a pendulum's clock rate.

Keywords:   pendulum, coarse adjustment, clock rate, bob, sleeve bushing, threaded nut

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