RC vs CC again

[Ron Nossaman]

>I agree with Ron on this one except that the starting point is important. 
>It determines the range of variations in humidity the soundboard can 
>safely live in. If your soundboard is going to live in New Orleans it 
>needs to be ribbed at a higher point than if it is going to live in Nevada.

But Steinway doesn't chose the dry-down MC based on where the pianos will 
end up, do they? They take a panel that was at whatever they use for a dry 
standard (4.5%?, 4%?) out into a room with the windows open and 80%+RH air 
blowing through to set the bearing, regardless of where it will eventually 
end up. Is that not the case? The soundboards have gone from 4.5%MC to over 
14%MC before they even get out of the factory. Yes, the starting point is 
important, but how can you build a flat ribbed CC board by drying it down 
to only 6%MC when you can't have any idea how dry it will be at it's final 
destination?


>O.K. I didn't say or mean to say "that the ribs of a compression crowned 
>soundboard supported most of the crown". What I was saying is that once 
>crowned and installed the panel of does not support the bearing load in 
>any significant way.

But it does. It supports the entire bearing load, as well as bending the 
rib. We're talking about different things, or at least the same thing at 
different points in the assembly process. Granted, it's not double what it 
takes to bend the rib into a crown in the first place because as you add 
bearing, the rib straightens and provides less resistance to crown. So 
you're right that the load increase doesn't all that significantly increase 
the panel load, but only because the crown is pressed down. The panel 
trades some of the diminishing rib load for the increasing bearing load. 
Ok, I got it. This is during assembly and stringing, where the crown 
initially formed by the panel compression bears little resemblance to the 
crown it becomes under string bearing load. After final assembly, the panel 
compression is the result of the sum of the force required to keep the rib 
bent and support the bearing load - at a given final crown height. That's 
what I'm talking about. The fact remains that the panel is still supporting 
both the rib and the bearing as long as any crown and bearing remain.

Ron N