rib radius

[Farrell]

Yes Del, that is exactly what I was trying to point out. I was also trying to relate to another common reference to the amount of crown a board might have: "That thar pie-anner soundboard has a full 1/4-inch of crown." That reference would mean that somewhere on the board, if you stretched a string on the bottom of the board from edge to edge, you would be able to measure a 1/4-inch deflection in the board from a straight line. As meaningless and imprecise as this reference to soundboard crown may be, it is the way many techs will describe crown. Although once a board is installed into a piano, it does become increasingly difficult to describe the curvature of the board using any method.

Terry Farrell
  
----- Original Message ----- 
From: "Delwin D Fandrich" <pianobuilders@olynet.com>
To: <pianotech@ptg.org>
Sent: Thursday, July 11, 2002 10:55 AM
Subject: Re: rib radius



  ----- Original Message ----- 
  From: Erwinspiano@AOL.COM 
  To: pianotech@ptg.org 
  Sent: July 11, 2002 6:35 AM
  Subject: Re: rib radius


  In a message dated 7/11/2002 4:31:37 AM Pacific Daylight Time, mfarrel2@tampabay.rr.com writes:

          Dittos Terry. 
      I Know of no on using less crown in the treble. At least many are using 60ft. thru out and many of us increasing radius into  the treble. I think the confusion is that a 60 ft. curve on a 40 inch rib appears to have proportionally more crown (7-8 mm) than a 15 inch rib with a 25 ft. curve ( 1.5mm) when observed visually. 
  >>>>>Dale Erwin>>>>>>>>

Dale & Terry,

Let's define our terms here. When talking about increasing or decreasing crown we're generally referring to the amount of visible curvature in the system -- a particular rib or the whole board. So an increase in crown means the system has more visible curve and a decrease in crown has less. It's the radius of the curve that is changing. Now, if we're talking about radius then a rib cut to a 40' radius has more crown than does a rib cut to a numerically larger 60' radius. Regardless of length.

We use ribs of smaller radius (larger crown) in the treble and ribs of larger radius (smaller crown) in the bass.

At least I think that's what Terry was referring to?

Del