Setting Downbearing was laminated ribs

[Erwinspiano@aol.com]

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Ron
  Beautiful post & description of the dilema of  setting down bearing in the 
real world that covers this practically.    When I was just getting started in 
the belly business I set up a Model A stwy to  11/2 degrees, calcluated 
without strings & without pre compressing  anything.  The result was that by the 
time I got the bottom half of the  tenor strung my wonderful downbearing 
calculations had disappeared in to  the gradually compressing sound board so that by 
the time I got to   stringing the first capo  there was zero degrees angle & 
hence no down  bearing pressure.  
    The resultant tonal failure could have been  devastating but fortunately 
I had used an adjust able plate suspension system  & was able to do some fancy 
adjusting & save the project without  starting over.  The information I used 
to set up the boards/bearing  came from an article  in the journal, by the 
way, & I later  chastised my friend who wrote them for not amending them to 
include  pre-stressing the board method, which he also had since switched to. Be  
careful what you read as the truth even in our own illustrious  journal.
   My compliments for providing some real numbers  & math
  Dale

A common  scenario with new pianos is for techs to 
measure a down bearing figure  which on the face 
of it looks OK, but very often the sound board 
has  sunken to a state where it is pushed almost 
completely flat by the down  bearing angle which 
was set into the piano. In these instances the  
board is too weak for down bearing loads which are 
being applied or  the unstrung angle wasn't set 
properly. Either the down bearing unstrung  angle 
should be reduced or the board strengthened to 
withstand the  setting angles to which it is being 
asked to resist. So often technicians  will look 
at a sound board and declare that it is fine 
because the  down bearing angle measures some 
wonderful figure. But if the board has  been 
pushed inside out before the customer's ink is 
dry on the cheque,  things ain't too good, 
regardless of what the down bearing gauge might  
indicate.

Get an accurate down bearing gauge and a thread  
length for looking at crown, and measure a few 
pianos old and new.  You'll develop a picture of 
what's happening.

Ron  O.





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