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

[Farrell]

Just for the record, I have a "rolled bridge" on my 1900 5' 11" Bechstein.
The whole long bridge is leaning forward. Put a straight edge on the bridge
top parallel with the strings and it quickly runs down below the level of
the strings on the forward/speaking side of bridge, and way up in the air on
the backscale side. Put a string on the bottom of the board and the area
between the long bridge and the belly rail has MAJOR reverse crown, but the
area between the long bridge and the curved side of the rim has nice
positive crown! A real "S" shaped soundboard! She is a beauty. And there is
no cantilevered bass bridge there - it is glued directly to the soundboard.

Now I am certainly not suggesting I know what caused this - did the bridge
roll forward and bend the soundboard, or did the part of the soundboard
collapse and suck the bridge down with it - kinda like the sink holes we
have here in Florida! I don't know. My guess is that it would be mostly a
soundboard problem - it certainly is now!

The base bridge actually rolls forward at the tenor end, and backwards at
note #1.

It will be interesting when I get the board out and the bridges off. I
wonder how much of the twist will be permanent in the bridge root. I figure
the possibility exists that I will need to make complete new bridges for it
because I may find excessive twist in them.

"Course, maybe Del will be redesigning the bridges for me anyway!!!!!

Hey Del. Is the little tenor bridge you speak of something you like to put
on all pianos under, say, 6-foot? In general terms, what are the factors
(now counting money or hassle - but rather only from a design standpoint)
that make you lean one way or the other. I saw an 1885 or so Steinway with
one, and my 1912 Mason & Hamlin 54" upright has one also. (The Steinway was
a joke - local dealer - new black paint, strings, hammers - looked good -
sounded eigh - $50,000 - I wish I could post what I am thinking).

Terry Farrell

----- Original Message -----
From: "Delwin D Fandrich" <pianobuilders@olynet.com>
To: <pianotech@ptg.org>
Sent: Wednesday, June 13, 2001 10:58 PM
Subject: Re: Rolled bridge: cause? diagnosis? treatment? Or maybe a floating
pinblock?


>
> ----- 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
>