More on soundboard crown

[Delwin D Fandrich]

----- Original Message -----
From: "Phillip Ford" <fordpiano@earthlink.net>
To: "Pianotech" <pianotech@ptg.org>
Sent: August 17, 2003 1:29 PM
Subject: Re: More on soundboard crown


>
> If it's a negative thing I wonder if making the top of the rim
> conform to the outline of the board without bending it along the
> grain would yield positive results.  Obviously just angling the top
> of the rim, as some builders do, isn't going to accomplish this.  But
> if you were to crown your board and then measure the shape of the
> outline and cut the top of the rim to match (which would mean
> considerable deviation from a plane) I wonder if there would be a
> beneficial result.

It didn't seem to help Kimball all that much. In fairness we'll have to
concede that the design and construction of these pianos had one or two
other problems. But I think they were the first to actually machine a full
spherical crown in the rim of their grand pianos. It has been common
practice with vertical pianos for years, if not decades. (It's much easier
to do with vertical pianos. It became easy with grands with the advent of
the CNC router.)


>
> As far as the panel cross grain not holding the required compression
> loads, how much is it supposed to hold?  I agree that it won't hold
> the entire downbearing load.  On good spruce isn't cross grain
> compression strength on the order of 500 psi?  Let's say you want to
> stay below 200 psi to prevent compression set.

That still won't "prevent" compression set. It will simply slow it down.
Any significant load on the wood will induce compression set--especially
perpendicular-to-grain.

Del