Curve on Bridge Bottom

[Farrell]

Comments below. Hey....I'm not shot!

Terry Farrell
  
----- Original Message ----- 
From: "Ron Nossaman" <RNossaman@kscable.com>
To: <pianotech@ptg.org>
Sent: Saturday, May 04, 2002 10:03 PM
Subject: Re: Curve on Bridge Bottom


> >Thanks Ron. I do see your point. I'll have to think and play on this a 
> >while. Seems like the bridge can really be subject to some distortion! 
> 
> Probably, though I'm not talking about distortion in this case, just the
> entire bridge rotating as the board collapses.

Yeah, that is what I mean - the bridge's orientation can get distorted. If that bridge is not on the top of the arc, the orientation of the bridge top would change (rotate) from when you planed it down to set downbearing, to when the piano was strung - perhaps not enough to notice.
  
> >I know you're going to want to shoot me for this, but after all you said 
> >about the curved bridge finding its place, or rather conforming, to the 
> >curvature of the board, this leads us to the folks that align the apex of 
> >each rib to the long bridge line - and maybe half-way between the long and 
> >bass bridge at that end. This always seemed kinda goofy to me - wouldn't all 
> >the ribs just rotate end-to-end and even out after you take the think out of 
> >clamps? I trust you do not do such a thing?
> >
> >Terry Farrell
> 
> Nah, I won't shoot you - just whack you a little with a question.
> Geometrically, can the high point of a circular arc segment be anywhere
> other than at the center of the chord defining the segment? You have one
> hour. Compass and straightedge allowed.

> Ron N

No compass and straightedge needed for this one. Yes, of course, assuming the inner rim bevel is on a horizontal plane (hope that is not tooooo big an assumption). I guess that was my question: No matter what gymnastics one may perform with soundboard clamps, won't everything just re-align itself once you install the board? I am understanding you to say yes! The reason I ask that is that I am aware that some very respected and prominent soundboard builders have the Gold, Silver and Bronze in clamp gymnastics.

But on many boards that don't have cut-off bars, or only have small cut-off bars, the bridge is nowhere near the middle of the board, and hence the bridge does not end up at the arc apex. I suspect the only way to improve that, short of installing a well-designed cut-off bar, would be to make un-symmetrical ribs and force the apex on the complex curve of the board underneath the bridge.

Is this one of the reasons to put in a good cut-off bar? To get the darn bridge into the center of the board? Or is the cut-off bar strictly to reduce soundboard area and minimize undesirable vibrations of the board?