Old Upright, partial plate, Pitch?

[Mike and Jane Spalding]

Dave,

Thanks for your post.  It's good to have the benefit of your experiences
without having to live through them, especially the one that made the big
bang sound!

As for the calculations, tension is proportional to the square of frequency,
so if you assume a 440 tension of 35,000#, as it was for an old upright that
I recently re-scaled/restrung, then at 435 it would be 35,000 times
435squared divided 440squared, or 34,209.  Tension reduction of 800#, a
little more than 2%.  At 1/2 step low, this piano is at 89% reduced tension,
or 31,180.

thanks,

Mike


----- Original Message -----
From: Dave Nereson <dnereson@dimensional.com>
To: <pianotech@ptg.org>
Sent: Thursday, August 09, 2001 3:14 AM
Subject: Re: Old Upright, partial plate, Pitch?


>
>   ----- Original Message -----
>   From: Mike and Jane Spalding
>   To: pianotech@ptg.org
>   Sent: Wednesday, August 08, 2001 10:49 AM
>   Subject: Old Upright, partial plate, Pitch?
>
>
>   List,
>      Can a partial plate upright be safely tuned to 440 or should it be
kept
> at, say, 435?
>
>   Although "standard" pitch was the so-called "International Pitch" (435)
> when many of these old uprights with 3/4 plates were built, I have raised
> many of them up to 440 as long as I had a good feeling about the piano
being
> able to take it (not scientific, I know) AND:  I tightened plate screws
> first, inspected for integrity of pin block, and no separation of plate or
> pinblock from the back, inspected for rusty strings & pins, strings that
> have been spliced or replaced, advised owner of risks, and preferably
filed
> & reshaped hammers and regulated at least lost motion and let-off first
(to
> give the hammer a firmer blow to the string to "get it vibrating real
good"
> to render through the bridge pins.  In 22 years of tuning, I've had only 1
> old upright "give way", that is, the soundboard "broke" somewhere, I
> guess -- I couldn't find anything obvious, but it sure made a big bang.
> Held pitch, though, and still sounded OK.  Soundboard and bridge damage or
> failure, and strings breaking, are more likely than the plate cracking,
but
> anything can happen, and apparently it's more risky with a 3/4  plate,
which
> is why Wim and others don't do it even with a full plate.  But I remember
> somebody else in this list saying, "440 or die!"  Probably better to err
on
> the safe side and leave it low.
>     The exposed pinblock itself shouldn't be of much concern; some
verticals
> with "full plates" have large openings for the tuning pin "fields" rather
> than individual holes drilled through the plate.
>       To the calculating techs out there:  what's the total tension
> difference on the plate between a piano tuned at 440 and one at 435 (for a
> typical scale design of an old upright)?   And what's the difference in
the
> total downward pressure of the strings on the bridge &
> board?      --Sincerely, David Nereson, RPT
>
>
>
>
>
>
>