more bridge design

[Barbara J. Fandrich]

----- Original Message -----
From: "Farrell" <mfarrel2@tampabay.rr.com>
To: "Pianotech" <pianotech@ptg.org>
Sent: Thursday, March 27, 2003 5:00 AM
Subject: Re: more bridge design


> I think this particular comment about the 30 lbs. was regarding a bass
bridge. If it is a bass bridge we are talking about, I would suppose the 30
lbs. is a fair number to use. Many rebuilders do not put any, or at most
minimal (some just have the bass strings "kiss" the bridge top) downbearing
on the bass bridge - so the bass bridge will have much less downbearing
force per string.
>
> Terry Farrell


We speak of string bearing as if there were some kind of universal constants
involved. As in "one-size-fits-all." It is good to keep in mind that all
string bearing settings are dependent on a variety of varying factors. Among
them are:
    --  String tensions. Both regional and overall. In general, string
bearing (the
        string deflection angle) is inversly related to string tension.
    --  Backscale lengths. Again, both regional and overall. In general,
string
        bearing is directly related to backscale length.
    --  Soundboard characteristics. Mass, stiffness, crown, size, etc.
Keeping in
        mind that these vary over the years. In general, string bearing is
directly
        related to soundboard mass, stiffness and crown.

The Bush & Lane grand we just finished up had an initial string bearing
setting of approximately 0.5º. Slightly less at the bass end, slightly more
at the tenor end. While the soundboard ended up with very little crown, it
was reasonably stiff and the backscale was exceptionally long. It has an
outstanding bass section. It all depends on the characteristics of the
overall piano design.

Del