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Subject: knife edge materials & horological update
From: holmstro@..........
Date: Wed, 14 Nov 2007 01:15:19 -0800 (PST)

The HSN website has some preliminary information on knife edges for
horology located at  A rounded edge is the
key to success as Chris points out.  If done properly, knife edge
supported pendulums for clocks can be a great success - Reifler clocks for

More appropriate to this discussion > The Granta Materials Intelligence
web site at
discusses material choices for knife edges from an engineering point of
view. The Granta site suggests that elastic and plastic deformation are
important varibles to control in a knife edge suspension. "Elastic
deformation is minimised by choosing materials with high Young’s modulus;
plastic deformation is limited by choosing materials with high hardness.
Granta suggests making a graph with Young’ modulus on one axis and and
hardness on the other and pick the materials with high values of both.
"The very best are all ceramics: boron carbide, silicon carbide and
tungsten carbide. If the selection box is relaxed so that the first metals
appear, the selection picks up medium carbon steel, high carbon steel and
low alloy steel. All are sensible choices: the ceramics when the ultimate
precision is required, the steels when robust design able to deal with
shock loading is needed."

re horology:

Indium is not a good material for flexures, it is very soft - I ment to
say Niobium (thanks Chris).  EDM shaped Niobium flexures qre used in
gravity wave detection pendulums - there must still be some losses but I
do not know how they compare to some of the rolling solutions disccused on
this list.  Seaching for niobium on the HSN web site horological
literature data base at yields 4 papers on
niobium flexures in a title search plus a couple more using a keyword
search.  Searching for flexures yields many more hits.  Note the BHM data
base currently has more than 12000 horological and horological science

Randall re Flex Pendulum

Bob Matthys contacted you re the flex pendulum.  He used a conventional
pendulum with a flexure conected mass above the center of rotation to
correct for circular error - the work was published in the Horological
Journal.  Bob's papers have been collected in a book published by Oxford
University Press.  The papers cover Bob's experimental work with clock
pendulums including flexures, teperature compensation, material stability,

Bob Holmström
Horological Science Newsletter


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