Curve on Bridge Bottom

[Farrell]

The only bridge I had laying around was from an upright and it was notched at the tenor/treble break, so I followed your suggestion over the 39" tenor segment - it bowed 5/16" with 100 lbs applied in the middle (my son stood on it).

I'm not sure what I was supposed to observe. Kinda seemed to act like a big rib.

Terry Farrell
  
----- Original Message ----- 
From: "Ron Nossaman" <RNossaman@KSCABLE.com>
To: <pianotech@ptg.org>
Sent: Thursday, May 02, 2002 9:54 AM
Subject: Re: Curve on Bridge Bottom


> >Yes, of course, absolutely. But the essence of my original question is: Is 
> >there not an advantage to preserving this rib-induced 
> >pre-bridge-installation soundboard crown with a bridge bottom machined to 
> >match the board crown (or perhaps you want to machine the curve you think 
> >you will have after board loading - whatever). It seems to me it's like 
> >installing 16 of 17 machine-crowned ribs, but putting the last one in flat - 
> >you know it will bend because there are already 16 on the board with a bend 
> >in them - probably won't make much difference.
> 
> And the essence of my answer was that whether the bridge is crowned or not,
> it is curved. Clamp a ribbed board in a piano so that long grain crown will
> form. Lay a flat bridge in place on top and the bridge will fit quite
> closely to the soundboard, just like a crowned bridge will. The bridge
> doesn't support or depress this long crown. It merely rotates as necessary
> to accommodate it. Grab a tenor/treble bridge with one hand at the low
> tenor end, laying the treble end on the bench (which has about the same
> flexibility of the soundboard treble). With pins up, and the other hand
> placed in the middle of the bridge, try to bend it. Observe.  
> 
> 
> >Again, I think I am really asking two questions here: First, from a 
> >practical standpoint - you have already said there doesn't seem to be much 
> >difference - I'll take you at your word. Second, from a theoretical 
> >standpoint - I should think there would be at least a theoretical advantage 
> >(and if so, perhaps a small, barely perceptible practical advantage - 
> >perhaps the practical advantage might only show up after thirty years, as 
> >maintaining original crown better?).
> >
> >Terry Farrell
> 
> Since the bridge isn't supporting the crown in the first place, I can't
> imagine how it will help support it in the long run. You measure reverse
> crown in a Steinway board, which you know has a crowned bridge. You tear
> the board out and find the bridge still nicely crowned and as stiff as it
> ever was - yet the board was reverse crowned. Where was the crown support
> from the long bridge? There never was any to my thinking - the bridge
> merely rotated and followed the board down as it went flat. I've read and
> heard from day one that the crown formed by the bridge was the most
> important crown in the soundboard. I just don't see anything either
> logically or demonstrably that supports the idea.
> 
> Some folks say they like the treble better with a crowned bridge, some say
> they detect no difference attributable to bridge crown. Each of these
> people builds a soundboard a little differently from the other. I say bless
> them all. They're doing what they perceive as working for them. If you feel
> that a crowned bridge will provide long term crown support, then crown your
> bridges. It may be beneficial, or it may not, but it won't do any harm that
> I'm aware of.
> 
> Ron N