Sound Board Crown

[A440A@aol.com]

 Richard Moody asks;

>How do you measure crown on a sound board?  (With strings attached)
>How much should there be?

      The most accurate, easy way I have found is to use a piece of white,
thin  1/4 "leader" tape "   . It is used to start reel to reel tapes, it is
NOT adhesive.

     Tape one end under the soundboard, at one edge,and then thread it over
the beams, etc.  to the other side, ( staying between the ribs, of course).
Make sure there are no twists and then, pull it tight and tape the other end
to the bottom of the board.
     You may be able to see a gap between the tape and the board,  it will
show up as a shadow between the tape and the board.  This is why you want to
use this very thin, white tape.  If you want to measure the crown,
accurately, then use a set of feeler gauges between the tape and the board.
 With a strong light shining on the shiny tape, it is very easy to get the
bearing  read to several thousandths, though that is not so important.
        You may want to measure the bearing at several places under the tape,
before you move it up or down several ribs.  Doing it this way can give you
an idea of the board's overall shape.

       Amount?  Seems like all pianos have their own optimum about of bearing
pressure.  It must be enough to tighten the whole structure, but not so much
that the sound board has been forced to it's elastic limit.

     I would be interested in how much downbearing others find appropriate
for old soundboards; who does what?

Regards,
Ed Foote