Soundboardcrown

[Farrell]

Hi Del. 

Ron N. wrote:  

> It would arc anyway because of the ribs, regardless of whether or not it 
> was glued to the rim. Are you intending the rim to maintain the crown?

That's what I was getting at. It sounded to me like he was expecting the board to expand, the rim to stay put, and thus put the crown in the board.

Del wrote:

> What Peter is doing is simply taking the compression out of the panel
> temporarily, letting the assembly flatten out, and then gluing it to the
> rim. As moisture goes back into the panel it once again becomes a
> compression-crowned soundboard assembly.

My understanding was that Peter glued the ribs to the panel while all were EMCed at 60% RH. The only reason there was a little bit of crown in the board before putting into piano was because he pressed the flat ribs into a caul that bent under the air pressure. So I suppose that would indeed put a little compression into the board. But then he dried it way down and glued it into the rim. I think he is under the impression that drying down the ribbed board and gluing it into the case is going to produce a bunch of crown because the rim will be rigid and support that crown.

That's why I suggested that process might not hold much water, let alone crown.

Terry Farrell
  
----- Original Message ----- 
From: "Delwin D Fandrich" <pianobuilders@olynet.com>
To: "Pianotech" <pianotech@ptg.org>
Sent: Tuesday, December 17, 2002 1:40 PM
Subject: Re: Soundboardcrown



> > Ron. I think what Peter is doing here is inducing a small amount of crown
> by gluing a flat rib to a flat panel in a curved caul at ambient RH. And of
> course, this will produce a small amount of crown. He then dries the board
> down and glues in into the piano. It would appear that he is relying on the
> rigid-rim-supporting-the-crown theory to keep the board crowned after it
> expands a bit with the increased RH. Obviously, there are a few of us that
> do not feel that theory holds much water, let alone crown.
> --------------------------------------------
> 
> 
> No, Terry, the rim doesn't really enter into it. If you take a
> compression-crowned soundboard assembly back to its condition at the point
> of ribbing the compression stress that holds crown disappears. In other
> words, if you belly a board at 4% MC using flat ribs and a flat press it
> crowns up in a normal room atmosphere. If you then take it back to 4% MC the
> crown disappears and the whole thing is more-or-less flat again.
> "More-or-less" because there has probably been enough compression set within
> the panel that, back at 4%, it would end up under some tension and go into
> reverse crown.
> 
> What Peter is doing is simply taking the compression out of the panel
> temporarily, letting the assembly flatten out, and then gluing it to the
> rim. As moisture goes back into the panel it once again becomes a
> compression-crowned soundboard assembly.
> 
> Del
> 
> 
> _______________________________________________
> pianotech list info: https://www.moypiano.com/resources/#archives
>