RC vs CC again

[David Love]

I have to say, I agree with Ron N.  that it's time to try and put real
science to this issue--though from my reading, I think Del and others have
done this many times over.  Many of the points being made are at such odds
that they cannot all be true.  The science must also pay attention to those
variables which cannot be held constant.  It is not enough to say that I
liked a soundboard that I heard that had some compression crowning
therefore compression crowning is a necessary component for a good sounding
piano.    Though I understand why that choice might be made, striving for
results which are quantifiable and predictable seems not to be a goal which
is unachievable.  And while I agree that isolating variables in a
controlled experiment is at best difficult, if not totally impractical,
those who argue one side or the other should certainly be able to
acknowledge those uncontrolled variables in their assessment about what is
contributing to what.    Though I am not an engineer, it makes perfect
sense that wood, as an engineering material, should behave predictably
within a certain range.   Unless personal bias is exercising undue
influence, I don't see why we can't come to some agreement about what that
is.  Though, as the late Carl Sagan observed, it is a demon haunted world!

David Love
davidlovepianos@earthlink.net


> [Original Message]
> From: Ron Nossaman <RNossaman@cox.net>
> To: Pianotech <pianotech@ptg.org>
> Date: 10/11/2003 2:11:52 PM
> Subject: Re: RC vs CC again
>
>
> >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
>
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