Down-Bearing for Old Board /AND YET MORE!

[Erwinpiano]

Hi Terry
        EIGHTY THREE SHIMS !   Wasn't that about half the soundboard area?
And you know there is no such thing as normal just bigger and not so big.
And so your not new or young( define that please.!  )
     The answer to your musing of the Big question is that you have deduced
correctly. Less crown/stiff less bearing more crown /& stiffness more
bearing.  By the way this antique method of bearing setting has beeeen
handed down to us from the halls of the famous  piano factories .   It is
quite reliable especially for the guys who are building there own boards and
know what to expect using there rib stiffness requirements.
   While  pounding on the board with my right hand I'm holding the strut
with  the fingers of my left hand and pressing the wedge with thumb of left
hand . Generally  if it's a rib crowned board , after about three thumps  on
the board  at the central strut will drive the wedge to a point where
further pounding   will  only feel like your pounding on a wood floor.  This
is an aquired feel.  If it's a compression crowned board (most older ones
are and I haven't removed a single board yet that showed any rib crowning.)
the crown will usually have shrunk a great deal and you could reverse
pound(crown) it with to many blows. It will have a different feel!
     At this point you have taken the slack out of the board and it's
stiffening up quite nicely as John hartman says.  I believe  this simmulates
about 6 to 8 hundred pounds of string pressure by pre- compressing the board
,which is probably only half the final amount of overall pressure at a -440.
So you can see that the extra 2 to 3 mm. gap measured at the string rest in
the pre-loaded state  will add extra pressure but not overload it your old
board.  In fact considering all the wood damage I would not pre stress it as
much .
    As Ron N said you can also do some weight loading test and get the same
or similar deflections . Take a deep breath it's not rocket science
fortunately (way tooo much stress in that field.
       Remember to pet the dog and hug the kids and control the our
collective obsessive compulsive tendencies.  We must after all feed the soul
as well as our Faces!
   Best Dale Erwin