Another bearing question - call for expertize

[John Delacour]

At 11:46 pm +0200 9/5/07, Stéphane Collin wrote:

>Have this gorgeous 1878 8 ft Bechstein...is this a sign that the 
>piano had too much downbearing, or not enough ?

At 2:24 pm +0100 10/5/07, I wrote:

>I find it's almost impossible to judge these situations without the 
>physical presence of the whole piano and the intuitive messages it 
>gives.  One possibility that occurs to me -- and I could easily be 
>quite wrong -- is that there was too much load on the bass bridge, 
>but then on this piano I guess there are only 17 or 19 notes on this 
>bridge, though at very high tension.

Hello again Stéphane,

I was out at the barn this afternoon and thought I'd take a look at 
an old Bechstein model VI grand (probably 1902) that I'm storing for 
one of the tuners.  This is not a great piano and I've told him I 
could use it for heating and will not get involved in its 
restoration.  Here's what I discovered today from a short inspection:

There is practically no deflection of any of the strings on the long 
bridge, but there is plenty on the bass bridge.  The bars are about 
26mm wide by 16mm deep.  In other words they have less than 1/3 of 
the effect of a common 25x25 bar.  This suggests to me that the board 
is designed to flatten out, or nearly, with a slight downbearing.  A 
ruler laid flat on the long bridge falls below the line of the 
strings and rests a little way above the string rest.  This suggests 
that the board has sunk from its intended level.

Now a straight edge laid along the ribs sits quite flat for most of 
the long bridge until the effect of the downbearing on the bass 
bridge begins to be added, and then the belly is pushed even further 
down so that it has "negative crown".  As you can imagine, this piano 
would win no prizes.  If the downbearing on the bass bridge were 
reduced, almost certainly, provided the belly still has any push left 
in it, the tone of the tenor and middle would improve a little.

While I was there I decided to see how much the board of the unstrung 
Kirkman would go down if I put 100lbs weight on the tail of the long 
bridge, where the unloaded deflection of a string is about 3 degrees. 
The bridge sank 0.8mm (1/32").

JD