Mason bearing quandry

[John Delacour]

At 9:36 pm -0400 9/5/07, Erwinspiano at aol.com wrote:

>   HI JD
>   Oh I love this stuff.  I'd love to see these pianos. From your 
>description it sound as if they have crowned ribs.  Any 
>cracks...ridges etc? This is how we learn important things.  Pianos 
>that have held up in climates such as yours without benefit of 
>modern climate control.  You know...what do I know?
>   The radii you describe are new board values. Fantastic. report 
>back on the end result sometime.
>   Also so the angular deflections are of the utmost interest.

Hello Dale,

I went out to the farm today ill-equipped to take proper measurements 
on the Kirkman and the light in the barn was not good owing to the 
return of more typical spring weather after the summeriest April here 
since records began.  The floor is now laid in my new workshop, next 
week it will be insulation, electrics and skylights and by June I 
should be moving in and be able to get on with serious work.

In the meantime I've taken a few pictures of the twin Kirkmans and 
made a few notes: <http://pianomaker.co.uk/kpsg/>. As you see, the 
angular deflection at the end of the long bridge is as ginormous as 
yours on the M&H.

I don't think I've ever seen compression marks on an English piano, 
and wouldn't expect to.  I've never seen them on a Bechstein either, 
but that's another matter.  Wolfenden describes well the traditional 
English way with soundboards, and Kirkman (the oldest English maker) 
will be one of the firms that established this:

"The writer's own formula is: Arch the bars to about the usual 
curvature, keep the board warm at say 10°0 to 120° F. for a few hours 
to shrink it.
   "Place it on a frame or board hollowed out a trace deeper than the 
curve of the bars, and while the board is hot glue the bars down.
   "When the pressure is released, the rounding will be rather greater 
than the original curvature of the bars, and the board in a condition 
of considerable compression, which it will retain and which will 
increase a little.
   "The backs of the bars, which by this prices become a little hollow 
in the length, are afterwards planed straight
   "The whole structure thus becomes a highly elastic spring."

This is a simplification of the process used by the best makers, I 
think.  As I show in the pictures, and as my measurements suggest, 
the Kirkman board is not given the same curvature throughout and only 
in the centre does the radius widen out to the traditional 60 ft.  As 
a result the bridge lies flat on a flat length of the board.  The 
inner rim slopes upwards quite markedly all round, at a much greater 
angle than the crowning of the board requires and this angling of the 
rim at the toe tends to, and does in fact, give curvature to the 
board along the grain as well.  All round the curved sides of the 
rim, where the plate sits, a beech strip about 3/16" thick is screwed 
above the board and this, and later the plate itself serve to clamp 
the board immovably at every point to the angled rim.

The inner rim on the bent side is several thicknesses of oak and is 
about 11-1/4" wide.  At the toe, the board is seated on a very soft 
hardwood curve of about the same width, and at the straight side it 
is glued to whitewood or pine.
These pianos are beautifully made and it is hardly possible that they 
would have chosen this soft light wood for reasons of economy instead 
of oak, of which Kirkman was very fond.  I can only think that it was 
discovered a more yielding perimiter at the toe was tonally 
advantageous.

I can't wait for the workshop to be finished so I can get everything 
moving again.

JD