evaluating sdbd. crown & bridge downbearings in a new piano

[Frank Weston]

Dale wrote:

>Sorry Frank,  This is simply incorrect .   When compression crowning,
>(flat ribs, flat press)  the board  is under no stress at all when it is
>glued.

Yes.

> Once the board takes on moisture the entire board is now under
>compression.

Yes and no.  If you talk in absolute terms, yes.  In relative terms, no.

>The curve is taken on because the top of the board is able
>to expand somewhat to relieve the excess compression.  The bottom of the
>board is glued to the ribs and does not have the luxury of expanding to
>relieve compression.

Thus the bottom of the board is in more compression than the top.  One might
conclude that the stress due to deformation which subtracted from the
compression in the top of the board and added to the compression in the
bottom acted as tension in the top of the panel and compression in the
bottom.  Think.  If the board were equally compressed top and bottom, where
would the moment come from to cause it to take a crown.

Frank Weston