AB Chase Concert Grand

[Delwin D Fandrich]

> -----Original Message-----
> From: pianotech-bounces@ptg.org [mailto:pianotech-bounces@ptg.org]On
> Behalf Of Dean May
> Sent: April 05, 2004 10:19 AM
> To: Pianotech
> Subject: RE: AB Chase Concert Grand
>
>
> Del: This is true only if there is some load coupling mechanism
> between the plate and the bellyrail and/or braces. (As with the Steinway
plate horn.)
> Otherwise the belly of the grand is not load-bearing.
>
>
> This makes no sense. Plates do not float on air. The plate bone is
connected
> to the rim bone (with the lag screw bone) and the rim bone is connected to
> the beam bone- and don't forget about the nose bolt bones. If the beams
> carried no load you would never see back frame separation in
> uprights. There would be no stress trying to pull it apart.
>
> Similarly, lifting the corner of a piano, thus flexing the wood/iron frame
> assembly, would never cause a piano to go out of tune if there was no
> connection.

Hmm. What I think I said was that unless there is some load coupling
mechanism between the plate and the bellyrail and/or braces the "belly" of
the grand is not load-bearing. This (when taken in context) means that the
bellybraces (which were, I think, the part of the structure under
discussion) do not bear any significant portion of the string load unless
there is some mechanism to couple that load down to them. There are many
pianos built with no such coupling mechanism. In these pianos the
bellybraces do not support the string load.

Obviously the rim of the piano does support the plate. But there is a
structural difference between supporting the weight of the plate and
positioning it above the soundboard and supporting string loads. There has
to be some mechanism to get the load down there.

In many grands there is no rigid connection between the front portion of the
plate and/or pinblock and the rim. And, no, a couple of large wood screws on
each end don't count. Dowels and glue joints do as long as they are still
structurally sound. But many pianos do not have glued-in pinblocks. So then
we have to consider how stress from the strings is supposed to coupled down
through the two ends of the pinblock, across a floppy bellyrail and into the
bellybraces which are supposed to be carrying all this string load. The
short answer is -- it isn't and they don't.

I might also observe that grands and vertical pianos are usually designed
quite differently. I don't recall the grand piano that would go out of tune
when one of three legs is lifted off the ground. Depending, I suppose on how
violently it is lifted. As may be, since the original discussion was about
grands I was referring the structure of grands. The load-bearing structure
of the vertical piano is a whole other discussion.


>
> If you want to argue that the load is designed to be carried by
> the plate, I can live with that. But it makes no sense to say that the
frame adds no
> rigidity to the plate or is not connected to it.

Within the context of the discussion at hand I thought that's what I was
saying.


>
> Del: It either case it is best if the bellybraces are spread across the
bellyrail
> to stabilize an otherwise rather floppy structure.

>
> You are both arguing my case. If the plate carries all the load,
> there is no need for more rigidity in the wood frame. All we need is
something to hold
> up a 400 lb casting. That doesn't take much structure. Three bar stools
> could handle it.
>
> I get the feeling that I am wading into an old debate. :)

You are. There have been several extensive discussions on the function of
the rim "bell." You might want to check the archives.

And I am not attempting to argue anybody's case. I am simply pointing out
that unless there is some specific mechanism designed to couple stress from
the strings down to the bellyrail and/or the bellybracing such as the
Steinway horn or the Walter coupling strap then the bellybracing is not
carrying and significant portion of the string load.

The rim bell is not intended to do this. Nor does it do anything to support
the bellyrail.

Del