[pianotech] FW: laminated ribs again

[Joe And Penny Goss]

Hi ron,
Was thinking of raising the board as wedge was driven in to create crown.
The kerf would as you say create negative crown.
The victim is an old upright with a cracled plate. Havent pulled it away
from the wall for an examination of the back post area but think that they
have given.
The design is a 3/4 plate still in good shape with a 1/4 cast plate over the
pin block area with big crack at the bass tenor break.
Joe Goss RPT
Mother Goose Tools
imatunr at srvinet.com
www.mothergoosetools.com
----- Original Message ----- 
From: "Ron Nossaman" <rnossaman at cox.net>
To: <pianotech at ptg.org>
Sent: Thursday, January 29, 2009 9:59 AM
Subject: Re: [pianotech] FW: laminated ribs again


>
>
> > Hi,
> > Dont know so Ima goina ask.
> > Is there a crown ridge that sort of follows the bridge line?
>
> In a rib that's a constant radius circle segment, the high
> point is ALWAYS in the center of the ribs. That's geometry, no
> matter what sort of "logic" and body english is employed to
> try to make it not so. If the bridge is centered on the rib
> then yes, the bridge is on the high point. If not, no. With
> non constant radius crowning (parabola, sine, catenary, or
> multiple radii), you can put the high point anywhere you like.
>
>
> > Could one cut kerfs in the ribs radiating away from the bridge line
> > and glue in wood shims
> > to induce more crown?
>
> Sure, if you really want negative crown, unless you kerf and
> wedge from the panel side. More geometry.
>
> Ron N
>