Soundboards/stress

[Jim]

Hi Bob:

comments are interspersed below.  Jim C.

On Fri, 27 Jun 1997, Robert W.Hohf wrote:

> Jim,
> 
> Thank you for your comments.
> 
> You said:
> "If you ever get a chance (time) to do another one,
> you might make a panel which is compressed across the grain as the ribs
> are glued on. Baldwin does this to avoid putting the convex side of the
> board into tension after the ambient air curving of the ribs and board."
> 
> Actually, I tried several methods to put one of my small panels into
>  compression but was unsuccessful.  Every time I applied pressure across 
> the grain (radially) the panel buckled.  My panels were only about 3/16" 
> thick--much thinner than a real board.  My understanding of the Baldwin 
> process is that they use flat ribs and a flat caul.  And you're saying that 
> they compress the panel while gluing.  This sounds very difficult.  How do 
> they do it?

There is an almost right angle caul to which the Bass and front edge of
soundboard is fitted to on the glue-up press. A curved fitted caul is
placed around the curves side of the board. This caul is squeezed about
1/8 inch to put pressure across grain while the board is being held down
by 2 or 3 unglued ribs while the others are being glued and set with the
go-bars. Mind you, this was the system use back in the early 70's. I
think they may have done away with go-bars by now. This system was 
used on all of the small grands. You are right that the ribs were flat 
and the table was flat. The 7' and 9' grands were pressed in curved
cauls using pneumatic pressure on each curved rib in a controlled
environment. I can't remember if these had cross grain pressure applied
while gluing up.

Jim Coleman, Sr.

> 
> Ron and Del,  I'm going to have to dig out my model soundboards and look 
> them over again, then get back to you.
> 
> 
> Bob Hohf
> Wisconsin
> 
> 
>