[pianotech] FW: laminated ribs again

[David Love]

Well yes and no.  The circle radius is constant so the 'high point', or full
height of the rib can be placed anywhere in proximity to the bridge by
tapering the bottom of the rib shorter on one side and longer on the other.
The only place this is really an issue is in the high treble (assuming a
bass cutoff is installed) where the bridge moves closer to the belly rail
relative to the inner rim on the bent side.  Here you can keep the rib at
full height under the bridge (or at least closer to the bridge) by
shortening the taper on the belly rail side and lengthening it on the bent
side.  I've done that on most of the boards that I've done without any
problem--or perceived benefit if the truth be known.  

David Love
www.davidlovepianos.com


-----Original Message-----
From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of Ron Nossaman
Sent: Thursday, January 29, 2009 9:00 AM
To: pianotech at ptg.org
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