compression vs rib crowning

[Delwin D Fandrich]

----- Original Message -----
From: "Ron Nossaman" <RNossaman@cox.net>
To: "Pianotech" <pianotech@ptg.org>
Sent: March 10, 2003 8:33 PM
Subject: Re: compression vs rib crowning


>
> >I can't speak for most of them--but Andre Bolduc feels very strongly that
a
> >duplicate board is *just that*. If you wish to redesign and send him
> >"specs" I'm sure he would be pleased to make a rib crowned board for
> >you--or if the piano had such a board in the first place he would "dupe"
it.
>
>
> How do you suppose he can tell what the crowning method originally was on
> an old board, and the original crown height at each rib? I sure can't.
>
>
> Ron N


Good question. By the early 1900s many enlightened pianomakers were
primarily rib-crowning their boards. They may have still been heating their
boards for gluing, but the crowning came from the curve cut into the ribs.
About the only way to tell for sure--and even this is not always
reliable--is to measure the height of the ribs in the middle and compare
this dimension with the height of the rib just before the feather. Some,
though not all, would crown their ribs only on the surface to be glued to
the soundboard. It was a cost-saving measure that also happened to work
well. Others, like Baldwin, crowned both the top and bottom of their ribs.
In these cases about the only way to tell is to see if there is any crown
left in the old ribs and board. If there is the chances are good that the
original was rib-crowned. There is the occasional compression-crowned board
that has held on to a bit of crown but after 50+ years of exposure to the
various elements they are rare.

Del