S&S D Duplex

[Delwin D Fandrich]

----- Original Message -----
From: "Richard Brekne" <Richard.Brekne@grieg.uib.no>
To: "Pianotech" <pianotech@ptg.org>
Sent: November 22, 2002 1:16 PM
Subject: Re: S&S D Duplex


> ...As far as I can tell from the little German I can read even Fenner
> will go along with the claim that this method of crowning results in a
panel
> that is more vunerable to enviromental conditions then so called rib
> crowning,
> tho I am not entirely sure I understand why this should be.  I understood
that
> actually machined curved ribs pressed onto panel which is set in flat caul
> would
> be most susceptible to cracking,

Is anyone actually doing this? I can't imagine why. It's the only crowning
process I can think of that would actually place the soundboard panel under
tension from the start.


>
> and that both the so called natural crown
> and
> rib crown had pretty much identical characteristics thus.

I'm not at all sure what you mean by "natural" crown. If it is some
factory's doublespeak for compression-crowning, the process is anything but
natural.


>
> This compression crowning is not quite the same as what is refered to as
> "natural crown" ?.  Arent these pressed into pressed into a dished caul ?
It is
> also my understanding that this results in a panel with very stabile crown
> (assuming reasonably stable environment)

If the ribs are flat before being glued to the soundboard panel it doesn't
matter if the cauls are flat or curved. The end result is a
compression-crowned soundboard assembly. Again, it is anything but a
'natural' process.


>
> >
> > I have two fundamental problems with compression-crowned
> > soundboards:
> >     First, they are unpredictable....
> >     Second, they have a highly variable useful life.

>
> Isnt this mostly indicative of either poor assembly conditions, poor
> handling,
> or lack of understanding of the vunerabilities in the process, and less
> indicative of that the process itself is fundementally flawed ?

Not really. Steinway is about as careful as anyone could be with this
process. Their controls are really quite good.

I have explained how this system places stress on the wood that exceeds it
mechanical strength capabilities in my Journal articles and, to a lesser
degree, on this list in the past. It's a lengthy explaination but it is
fairly basic wood technology.

Del