Crown without soundboards

[Ron Nossaman]

Hi michiel,

I agree with him too, and he agreed with me, and I agree with you. All three
of your points listed below are absolutely correct in the context of how you
mounted your ribs.  It's just that you are talking about something a little
different than I was; the forth point. I'll try to explain.

What you have just described is what Del calls a "compression crowned"
board. What I was trying to describe, was a board where the ribs are cut to
a crown before assembly, so the *stiffness* of the rib helps hold up the
downbearing of the strings. Since the rib doesn't start out flat, having to
be bent to crown, it's stiffness *helps* the panel hold crown, instead of
fighting it. 

If you had machined a crown in your ribs before assembly, you would have
gotten a very similar final crown in the board, with a lot less compression
stress on the panel. This would satisfy your three listed points, except for
a modification of number one. The string load would then be shared between
the rib stiffness and the panel. I would think this would be particularly
important when you re-rib an old board because the old panel won't take the
compression forces of a new one, and would need all the help it can get.
This machining a crown into the ribs to help support the overall soundboard
load is what Del has been describing and advocating all along, and it makes
perfect sense to me too.  


>BTW. I agree with Tim Keenan.
>The panel is NOT the ONLY thing supporting the crown.
>1. The panel takes care of the pressing forces in the whole construction
>perpendicular to the wood fibres.
>2. And the ribs take care of the stretching forces parallel to their fibres.
>3. The gluejoint keeps both opposite forces in balance.
>Take one the three away and you have a problem.
>Please correct me if I'm wrong.
>
>Michiel van Loon
>Meppel
>Nederland
>http://www.xs4all.nl/~mvanloon
>tel/fax ++31 522 255160
>

 Ron Nossaman