Rolled bridge: cause? diagnosis? treatment? Or maybe a floating pinblock?

[Delwin D Fandrich]

----- Original Message -----
From: "J Patrick Draine" <draine@mediaone.net>
To: <pianotech@ptg.org>
Sent: June 13, 2001 5:34 AM
Subject: Re: Rolled bridge: cause? diagnosis? treatment? Or maybe a floating
pinblock?


> Am I correct in my observation that the learned discussions of killer
> octaves, soundboard stiffness, soundboard crown, and downbearing
> seldom (if ever) refer to "rolled bridges"? I.e. that it's not a
> matter of bridges wandering, but rather collapse (lack of stiffness)
> of the soundboard in the desired areas.

I certainly have never connected the idea of a 'rolled bridge' with the
problem of the killer octave.  You are correct, it is a matter of loss of
stiffness through the affected areas.



> I've never felt comfortable with discussions of "rolled bridges",
> especially when it came to advice to *not* raise pitch to A440 on an
> older piano out of a fear of rolling.

I don't really understand just how a bridge is supposed to 'roll.' Once the
piano is strung and at pitch (initially) there just is not a lot of mass
string rendering through, or across, the bridge surface. To get the bridge
to roll apreciably, it seems to me that you would have to stretch out the
backscale quite a lot and all at once. Otherwise the bulk of the string
backscale will be holding the bridge in place while you pull around with
just the one.

As someone else already mentioned, there is often a problem with distorted
soundboards around cantilevered bridges. There is also a problem of a
sometimes significant depression in the soundboard at the low end of the
tenor bridge common to compression-crowned soundboards if the tenor bridge
is overloaded. Neither of these problems can properly be called 'rolled
bridges.'



> PS The write up for Del Fandrich's class "Designing and Remanufacturing
the Small > Piano" states that "Much of the material covered appears in the
instructor's book of > the same name." Is there an upcoming  publication
date?

In my head there is. But then it's already fully written in my head--the
problem is getting it into the computer. That is somewhat difficult. At
least for me, it is.

I had hoped to have it ready to print by this year's convention. Not a
chance. I'm about two-thirds through with the text, but tons of work to do
on the illustrations and drawings.

Del