evaluating sdbd. crown & bridge downbearings in a new piano

[Richard Moody]

----------
> From: Delwin D Fandrich <pianobuilders@olynet.com>
> To: pianotech@ptg.org
> Subject: Re: evaluating sdbd. crown & bridge downbearings in a new piano
> Date: Thursday, September 23, 1999 12:45 AM
> 

> 
> So.  Keeping in mind that, if it weren't for that pesky rib, the entire
> soundboard panel -- top, middle & bottom -- would really like to be about
> 1,020 mm wide at this point, please explain to me how there can be any
> tension anywhere in this panel. ........ .... ....
> however, there is compression stress within the entire panel.  And it is enough 
>to keep that rib bent.


Here the panel is "bowed" or "arched".  If the wood is not under "tension" in this
case, it must be a matter of word meaning.  _tension_ "the stress resulting from the
elongation of an elastic body --- contrasted with 'compressive stress'  " 
	The word  "tension"  apprears to be used in place of "compression stress" In either
case the wood is under stress due to expansion. I suppose there is a big difference
here since tension involving only two opposing forces produces *stretching*, and
compression can result in *bending* (which cannot happen with tension) which creates
another force acting at right angles to the compression forces, giving an added
quality of elasticity.  If no bending no effect on the accoustic properties of the
sb,, I tink... ---ric




> 
> Now, don't take my word for this.  Actually try it.  Get the wood.  Cut it,
> glue it and cook it.  Watch it work.  As I said in another post, this is
> really basic wood technology.  The more you know about it, the better you
> will understand the piano.  And sometimes the best way to really learn
> something is get your hands dirty.
> 
> Del
> 
> 
> 
> 
> ----- Original Message -----
> From: Richard Brekne <richardb@c2i.net>
> To: <pianotech@ptg.org>
> Sent: Wednesday, September 22, 1999 1:34 PM
> Subject: Re: evaluating sdbd. crown & bridge downbearings in a new piano
> 
> 
> >
> >
> > List:
> >
> > After reading Dels last post on the issue I have become convinced that
> > the term "compression" is at the root of the "dissagreement" or at least
> > my own problem grasping all this. For my own part I believe the whole
> > thing could be cleared up if one of you would explain just how a board
> > curved by force or by use of humidity can be "Compressed" on the upper
> > surface. I can easily see how compression applies to the bottom side,
> > but I cant get past this idea that the convex side is "stretched" rather
> > then "squeezed".
> >
> > >From what I was able to gather from Dels last, it seems like this has
> > something to do with cell structure and how it reacts to differing
> > stress. In any case.. I would really really appreciate somebody clearing
> > this up.
> >
> > Richard Brekne
> > I.C.P.T.G.  N.P.T.F.
> > Bergen, Norway
> >
> >
>