Cutting rib radii

[David Love]

Thanks for posting those pictures.  Admittedly, I’m having a hard time
visualizing how you use all this to actually cut the rib.  

David Love
davidlovepianos at comcast.net
www.davidlovepianos.com 


-----Original Message-----
From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of Jude Reveley/Absolute Piano
Sent: Friday, August 08, 2008 5:41 AM
To: Piano Tech List
Subject: Cutting rib radii

 
As for methods of cutting rib radii:
 
There's ye ol' router sled (see picture). You'll need one per radii. Michael
Morvin makes the best templates (picture posted) for all your crowning jigs
from rib presses to cauls to sled runners (picture posted) and I bought a
few before I finessed my router base, based on the old sailor's trick that
Andrew Anderson described or Ron N. You'll need to know the deflection for
any given radii which is r-(r^2-(c^2)/4)^0.5 where r is the radius and c is
the span. I readily admit that while this router base works outstanding, it
was way more expensive to put together than buying Michael's templates.
 
I only have one "fixed sled" which I've used for the longest ribs on my more
traditional projects based on a 50' radius (I thought this was quite
aggressive when I was young<G>). This was supplemented by variable radii
ribbing by an adjustable crowning sled (see pix). This sled works
surpisingly well and I never went beyond the working model which I built
eight years ago. It crowns ribs up to 90cm in length. The center of both
runners are supported  by capstans, which refine the crown as well as
support the weight of the router. I set the crown by turning the turnbuckle
underneath, adjust the capstan in the middle and verify crown by sampling
measurements  every inch on each side with a height gage. As far as
thousands of an inch can measure, I'm producing arcs but even if they were
catenaries or parabolas, it doesn't matter.
 
 
Jude Reveley, RPT
Absolute Piano Restoration, LLC
Lowell, Massachusetts
(978) 323-4545