[pianotech] crown and radius

[David Love]

Like Ron says you have no choice about high point and bridge location but
you can alter the bridge tapering if you feel that you want the full height
of the rib to be located more under the bridge.  

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: Sunday, June 14, 2009 7:56 PM
To: pianotech at ptg.org
Subject: Re: [pianotech] crown and radius

Gene Nelson wrote:

> ****Hopefully I can describe this so it makes sense:
> As I consider how the radius are cut onto the ribs - pulled and clamped 
> into a caul mounted onto a sled on a table saw - the high point mark on 
> the rib (bridge location) is aligned to a mark on the caul on sled and 
> the finish height cut is made simultaneous with radius arc. The mark on 
> the rib (high point) may not be in the center of the rib. Example: on a 
> 12 inch long treble rib the high point may be 4 inches from the belly 
> rail and 8 inches from the inner rim. It would seem to me that the 
> radius circle should still be uniform??. It would also seem to me that 
> if the high point were centered on this 12 inch rib, the bridge would be 
> located so far away from it that there would be considerably less crown 
> available for it. Make any sense?
> 
> Gene

Not a bit (sorry). That's the pretty much universal 
description of *intent*, but doesn't have much of anything to 
do with result. Try it with a piece of scrap wood. Make a rib 
about 18", or a half meter (Can I butcher linear measurement 
systems like this without losing the logical point?), and put 
the high point of the CONSTANT RADIUS crown as FAR OFF CENTER 
as you can. Feather it, as you do, prop it up on identically 
sized blocks, and measure where the high point of the crown 
is. It will be, I guarantee, unless you made something other 
than a constant radius crown, in the center of the rib. It 
matters not how you hold your tongue during the measuring and 
cutting process, the high point of the resulting arc segment 
defined by a chord will always, always, always, pending the 
refutation of basic geometry, be in the center of the chord. 
This isn't something that's going to bow out to intuitive 
"understanding". It's part of the marrow of reality.

I chose the half meter as a reasonably handy size that 
wouldn't waste unnecessary material, and would be easy enough 
to measure. You could make it 40 meters long to similar 
effect, but it would be marginally more expensive and 
difficult to produce.

That's it. It's not my claim, by discovery, or my invention as 
a desperate attempt to be right at any cost. It's an 
observation of principle that has been known for thousands of 
years, in every corner of science but piano technology.

I just think it might be time we caught up with the 
civilization that built the Parthenon.

Ron N