Rib overkill

[Farrell]

I've disembowlled several old (pre-American/Aeolian) Knabes and am sure they machined quite a bit of crown into their ribs. I've got a strung 1902 6' 4" Knabe in my shop now waiting for a new board that has pretty good downbearing and a good 3/16" of crown along the longer ribs and 1/16" to 1/8" in the high treble and treble areas. I just measured a 44-inch-long rib off an old Knabe upright - it has a full 5/8" of crown to it (this would work out to something like about a 25-foot radius crown). Was anyone a hundred years ago using crown radii tighter than 25 feet?

Terry Farrell
  
----- Original Message ----- 
From: "Delwin D Fandrich" <pianobuilders@olynet.com>

> ----- Original Message -----
> From: "Sarah Fox" <sarah@gendernet.org>
> >
> > In a rib-crowned soundboard, the spring action is in the rib.  However,
> ribs
> > are made of wood, and wood eventually loses shape under constant
> pressure.
> 
> Lot's more things to go wrong. Besides, in a rib-crowned soundboard system
> the ribs are quite long-lived. The stresses are moderate compression along
> the top of the rib and moderate tension along the bottom. This is what the
> wood fibers were created for and they handle the stresses quite well and
> for quite a long time.
> 
> Del
> Delwin D Fandrich
> Piano Designer & Builder
> Hoquiam, Washington  USA
> E.mail:  pianobuilders@olynet.com
> Web Site:  www.pianobuilders.com