[pianotech] Measuring Crown Radius

[Delwin D Fandrich]

1)  Both the inner rim (or skeleton) and the outer rim are laminated up as a
unit in a single stepped press.

2)  It is inherently unstable. Yes, the ribs do act to remove crown as they
try to straighten themselves out. Yes, at any time the MC of the board
increases the rate of compression set accelerates and (often) compression
damage occurs in the panel.

ddf

Delwin D Fandrich
Piano Design & Fabrication
6939 Foothill Court SW, Olympia, Washington 98512 USA
Phone  360.515.0119 — Cell  360.388.6525
del at fandrichpiano.com — ddfandrich at gmail.com


-----Original Message-----
From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of John Delacour
Sent: Thursday, July 14, 2011 2:52 PM
To: pianotech at ptg.org
Subject: Re: [pianotech] Measuring Crown Radius

At 16:22 -0500 14/07/2011, Ron Nossaman wrote:

>In CC crowning, the panel is dried down, then glued to flat ribs. 
>Panel expansion as it takes on moisture then bends the ribs into a 
>crown. The piano case isn't involved in the process, and the ribs 
>needn't necessarily be dried down.

Whether they are or not would surely make quite a bit of difference. 
If the case is not considered (by Steinway's for example) to be involved in
the process, why do they glue the case to the rim before fitting the
soundboard, thus causing themselves a lot of tiresome work that could be
avoided if they glued down the soundboard before attaching the case, as
many, if not most, makers do?

However that may be, the method seems to me inherently unstable.  For one
thing the bars (ribs) will ever afterwards be acting to remove the crown,
won't they?  If at any time the moisture content of the board rises to a
point where the board proper is crushed, then the bars will be keen to relax
and pull down the crown.

JD