Soundboard drydown for installation

[Farrell]

> On the one hand one states that the edges of the panel will simply crush 
> as it attempts to expand when constrained in the fashion the <<buttressed 
> arch>> idea employs.

I'm just really pulling that out of you-know-where based on observations. 
Spruce is very soft. When I'm building panels and clamping on edges, etc. I 
readily observe how easily you can crush an edge surface with a panel clamp.

Perhaps unrelated, but none-the-less interesting and perhaps unknown to 
many, is how much and how easily one can reduce the cross-grain dimension of 
a thin spruce panel when clamping. I've never measured it, but I would 
estimate that one could reduce the width of a meter-wide panel by 5 to 10 mm 
with only finger torquing on a few clamps. Spruce is very spongy that way.

> Yet Ron reports that the panel thus constrained simply didn't take on any 
> crown. These two strike me as mutually exclusive.

Hmmmm. Doesn't strike me that way. I don't see that one has anything to do 
with the other. And even if one were to expect some crowning from the rim 
constraint, if it didn't crown, the crushing of the panel at the edge might 
be a factor causing the lack of crown.

Again, I agree with Ron - the darn thing won't crown anyway from rim 
constraint.

> If the edges indeed would simply crush when subjected to such pressure ... 
> then what would prevent his experiment board from crowning ?

If the edges simply crush from rim constraint, then the rim is not any 
longer providing any force to the panel to promote crowning (if one were to 
believe that it could).

> If the edges are strong enough to keep the panel from crowning, then it 
> would seem to me that they are strong enough to help support crown if they 
> were first asked to..... which of course is a different question all 
> together.

Well, actually, that is what I thought you were asking. I agree, that if one 
believes that rim constraint causes crown, then a panel edge that resisted 
crushing would indeed be part of a crown-making system.

But I think all of that is hogwash. Either the panel supports crown (at 
least for a while) in a compression crowned soundboard system, or the ribs 
support crown in a rib supported system, or some combination of the two. I 
think I was running at the mouth more than anything with any comment I made 
about panel edges crushing and whatnot.

Terry Farrell

----- Original Message ----- 
From: "Richard Brekne" <ricb at pianostemmer.no>
To: <pianotech at ptg.org>
Sent: Saturday, January 19, 2008 6:27 AM
Subject: Soundboard drydown for installation


> Hi Terry.
>
> This is another bit that has bothered me ever since Ron's experiment 
> article.  On the one hand one states that the edges of the panel will 
> simply crush as it attempts to expand when constrained in the fashion the 
> <<buttressed arch>> idea employs.  Yet Ron reports that the panel thus 
> constrained simply didn't take on any crown. These two strike me as 
> mutually exclusive.  If the edges indeed would simply crush when subjected 
> to such pressure ... then what would prevent his experiment board from 
> crowning ?  If the edges are strong enough to keep the panel from 
> crowning, then it would seem to me that they are strong enough to help 
> support crown if they were first asked to..... which of course is a 
> different question all together.
>
>
>    'Course, none of this actually works - the ribs won't shrink much,
>    the panel
>    top edge will just crush when it expands the 1/10 mm that it might
>    move and
>    the rim has enough flex to negate any "arch" support.
>
>    Terry Farrell
>