Grand Bending & Square Grand Cheek Lift

[Farrell]

What is the "spine" in a square grand?

Terry Farrell

----- Original Message -----
From: "Clark Panaccione" <threesixesinarow@yahoo.com>
To: <pianotech@ptg.org>
Sent: Sunday, September 23, 2001 12:19 PM
Subject: Re: Grand Bending & Square Grand Cheek Lift


> Farrell wrote:
>
> > Can anyone quantify the potential problems? I can
> see that regarding
> > the belly, it will lessen  downbearing, and
> regarding the action, it
> > will cause the action frame to not sit flat on
> keybed, or if it does
> > curve with the keybed, the hammer height will get
> affected, etc.
>
> The construction of squares is that the action sits
> where effective framing might be. This is counteracted
> a little for late squares which have substantial
> wooden nameboard stretchers and nearby bass struts,
> but their effect is lessened by over stringing and
> relatively high tension. Bottom boards often are
> oriented to the main direction of the strain but which
> are coupled mostly through the case sides, with grain
> oriented parallel to the bottom which can distort some
> even before transmitting some of the burden to it;
> further, if a bottom is solid, it cannot resist any
> non-longitudinal, twisting strains so well.
>
> Another weak point in old squares is at the
> intersection of the spine and treble end of the wrest
> plank, a sort of sinusoidal distortion can be observed
> by sighting along the spine. Even while there may be
> no such evidence, you may see a flange or thicker
> section of plates in late squares around this same
> area.
>
> > The question being, does the amount of cheek lift in
> an old square
> > grand change much with strings in or out?
>
> Yes, but probably you're familiar with compression set
> through Del Fandrich's posts regarding soundboards.
> This is another sort of creep, like to old shelves and
> beams sagging under continuous load which will spring
> back when the load is removed but not fully.
>
> > Do we ever see piano case bending (front to back) in
> a
> > modern/traditionally designed grand ... ever bend up
> (front to back)
> > under string pressure?
>
> It is very common in old wooden framed grands. I just
> checked my oldest grand, ca. 1860 which doesn't
> exhibit this - however, its top strut is 70mm high and
> which is mortised into the cheek.
>
>
> Clark
>
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