Killer Octave Question

[Farrell]

I've done some playin' and some tinkin'. And I've decided that there is a difference between a crowned bridge, but that the difference, in practical terms, is negligent.

If you cut a circle out of cardboard one foot in diameter, and then cut a circle out of the middle of that, let's say eight inches in diameter, you have a big flat donut. Set that donut on a basketball so that it sets like a topless hat. Now also realize that you need about a foot of tangent coming off the donut at some point (low tenor or long bridge). Now you can see the argument for a crowned bridge. Or perhaps not really just a crowned bridge, but a bridge that has a bottom bevel in the treble area and a crown in the lower tenor.

Now back to reality. Soundboards, even Fandrich soundboards, have a larger crown radius than a basketball, and a bridge is only 32 or 35 mm wide. So I do suppose that the ribbed soundboard panel and bridge itself will conform quite readily to the very slightly mis-matched straight bridge and curved soundboard panel. The tenor end will bend enough (what, maybe 1 mm) and the treble section of the bridge can have a top whose plane is not quite parallel to the plane of the bridge bottom/panel top interface. Bottom line: any difference is close to or wholly within common woodworking error and completely negated by the flexibility of the woods.

That make sense?

Terry Farrell
  
----- Original Message ----- 
From: "Ron Nossaman" <RNossaman@cox.net>
To: "Pianotech" <pianotech@ptg.org>
Sent: Sunday, April 13, 2003 12:02 AM
Subject: Re: Killer Octave Question


> 
> >FWIW: I just cut a long bridge out of an old Mason & Hamlin and it is as 
> >flat as a pancake. Not a speck of crown to be found.
> >
> >Terry Farrell
> 
> You can tell? How tragic. One of the points I try to illustrate in my 
> bridge building class is the difficulty in determining whether or not the 
> original bridge was crowned, and how important it is to the assembly. An 
> old Knabe bridge, lying on a table and propped up in the middle with a 
> pencil, shows a lovely crown from end to end. Pull the pencil out, and it's 
> dead flat. That bridge will lay on a crowned soundboard and very nicely 
> conform to the crown of the board.
> 
> Ron N
> 
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