RC vs CC again

[Ron Nossaman]

>I am not endorsing a particular method. I certainly am not thinking that 
>Steinway has it right. I mite as well not be in business if I thought 
>that. But I am not inclines to take a jab at them every chance I get. I 
>was just pointing out that one should take into consideration the 
>environment that the piano is living in to set the moisture content at the 
>time of ribbing. Dale says he uses 5.5 to 6% because his environment is on 
>the dry side while I here in the north east find that 6.5% is best.

John,
Is it too much to ask to expect to stay on the subject of what's supporting 
what in a compression crowned soundboard, or is that just more sloppy 
thinking on my part? Dale rib crowns, as do you. It is a different system, 
with different load distribution characteristics as you ought to know, and 
as such, requires different assembly methods and parameters. I'm not 
looking for endorsements, merely attempting to make a point in context of 
building compression crowned boards with flat ribs.


>Well you can if the cauls are deep enough. None of us know for sure how 
>dry it will be at it's final destination. We already talked about the 30% 
>RH window. It applies to all soundboards.

And as has been discussed and pointed out many times, whether the panel 
compression is achieved by excessive drying, or deeper dished cauls, the 
resulting panel compression in a compression crowned soundboard assembled 
with flat ribs will be similar in other flat ribbed compression crowned 
assemblies with similar resulting crown. The final crown in otherwise 
identical assemblies is determined by the produced panel compression rather 
then the precise dry-down MC. That's in a compression crowned soundboard 
assembly with flat ribs.


>I am willing to consider this as true. But I still say that if the panel 
>does not exceed its elastic limit the stiffness of a PC board will be the 
>same as the stiffness of a RC board as long as the ribs are the same 
>dimension. My argument has been against the notion that the method of 
>crowning a soundboard has a direct effect on its stiffness.

And the final stiffness of the board has nothing whatsoever to do with  the 
current discussion. That is a different issue altogether. We are talking 
about load distribution and material stresses in compression crowned 
soundboard assemblies using flat ribs.


>Panel crowning's chief weakness is that the soundboard must be kept within 
>a narrow range of RH. But if it is kept in that range its performance 
>acoustically and mechanically should not be any different than a similar 
>rib crowned board.

Once again, this has absolutely nothing to do with the current discussion, 
which is about load distribution between panel and rib in a compression 
crowned soundboard assembled with flat ribs, and the long term 
ramifications of same.


>I have been getting the impression from some of the posts on this topic 
>that it was understood that a PC board would just instantly fall apart. 
>The poor week panel holding everything up. I think that that is a an 
>exaggerated claim clearly aimed at embarrassing the manufacturers and 
>rebuilders using this technique. Maybe I have this wrong but this strikes 
>me as an impediment to studying how these things work.

Then by all means, let's discuss the subject at hand instead of everything 
but, and attempt to actually learn something along with getting 
impressions. The last time I checked, the subject was on the compression 
levels present in the panel of a compression crowned soundboard assembled 
with flat ribs; how it is that the ribs could possibly be contributing to 
crown support, the effect of string bearing on panel compression levels, 
and how all this affects the longevity of the assembly. Staying somewhere 
in the ballpark of this subject might possibly help to generate some useful 
information.

Ron N