Question

[Delwin D Fandrich]

| -----Original Message-----
| From: pianotech-bounces at ptg.org 
| [mailto:pianotech-bounces at ptg.org] On Behalf Of Ron Nossaman
| Sent: March 30, 2006 9:15 PM
| To: Pianotech List
| Subject: Re: Question
| 
| It always used to be (DOWN to) 4% for CC (with a 60' crown 
| radius, however that worked), then...  Somewhere during the 
| soundboard crowning discussions on the list in the last few 
| years, it was reported that CC boards were suddenly and 
| mysteriously made with 4.5%MC. Then, somewhat later, 5%MC. I 
| think I recall the last report as being at 5.5%MC. Wishful 
| thinking aside, I somehow doubt that a reasonably functional 
| CC board can be built at 5.5%, or even at 5% and survive for 
| any length of time. Still, times change and the rules of 
| physics do seem to be negotiable in marketing.
| 


Actually you can end up with a CC board even if it is at 6% MC when ribbed.
Probably even higher. I don't know how far you could stress the system before
you started running into problems. 

You just have to press it up in cauls with enough crown. Still, of course, with
flat ribs. Don't ask me what that caul radius might have to be -- I've no
interest in working it out. As may be, if the caul radius is tight enough the
finished assembly will come out with the panel under compression and stressed
exactly as it would be if the panel were dried to 4% MC at the time of pressing.


Compression is compression regardless of how it is achieved. This, despite the
conversation I had some time back with a "knowledgeable" factory technical
person who insisted his companies soundboards were no longer compression-crowned
because the panels were now being glued up at something over 5%. They were using
flat ribs and curved cauls. If the ribs started out flat and the assembly ends
up curved it's a compression-crowned soundboard system.

Del