Soundboardcrown

[Ron Nossaman]

>I do not say and don't have said the board was going flat by drying it.
>I only eye-checked it and saw that some crown has disappeared compare
>whith the crown the board gets when it comes out of the press.  I don't
>have checked it with a straight piece of wood.  It was just by eye.

Oh, I thought -
>  But now, when I'm heating it to dry before gluing it in
>the piano, and checked it with a straight piece of lumber I have crown
>(about 12, 13 mm) across the ribs, the highest point of the board is
>where it has to be, and I see  a little bit of negative crown along the
>ribs (although this could be caused from heating the board, so it'll be
>warmer in the center as on the ends)
- meant the board was going flat (that's along the ribs) as you dried it. 
Which is, as I said, exactly what I would expect.



> >Why would you dry it to
> > glue it in the
> > piano when you apparently didn't to glue on the ribs? I don't
> > understand.
>It is not that difficult to understand.    When you dry it, it became
>flat  to place it in the piano; when it's done, because of the higher
>humidity of the environment, it has to swell, ie taking an arc because
>it can't move freely anymore due to the glue.

It would arc anyway because of the ribs, regardless of whether or not it 
was glued to the rim. Are you intending the rim to maintain the crown?



>I only
>know that using compression crowning needs more force to bend ribs and
>board and, I have to say, I hope that using this method gives more
>strenght and stiffnes to the ribs (ie, soundboard).

A rib crowned board can be built stiffer, for a given panel thickness, than 
a compression crowned board. The result is more controllable, dependable, 
and longer lived.


>Isn't this the
>ultimate goal?  Please do correct me if I'm wrong.

Controlled stiffness and mass is, I think, the ultimate goal.

Ron N