Downbearing

[rhohf@eagle.idcnet.com]

Does anyone know the source of the "One-fortieth Rule"?  Nick Gravagne wrote
about it in 1984 and I have seen several other scanty references to it in the
literature.  It seems that it was (is?) factory practice to aim for a
downbearing force of one-fortieth of the string tension.  It happens that a
piano with average 160#/string tension (4# downward force/string) requires
string deflection angle of 1.5 deg.  This measurement was apparently set on an
unloaded board so the  actual force would have been considerably less.

Bob Hohf