Keyboard frame question

[A440A@AOL.COM]

Del writes:
<<>Interesting. During the 70s and 80s S&S practice was to bed the keyframe
>with the ends just off the keybed surface so that the blocks would pull them
>down slightly when seated and screwed in place. The idea, I was told, was to
>be sure the front rail would remain snug to the keybed surface even if the
>rail were to warp slightly.<< 

    I had it explained to me that the keyframe was actually expected to be 
straight,  and the keybed had a very slight bow in it.  When the key blocks 
were pulling the frame pins down just enough to touch the keybed, one could 
be assured that there was contact from end to end.  On most pre 1950 or so 
pianos, this usually works wonderfully, (assuming the glide bolts are out of 
the way, and the action frame is evenly resting on all its cleats.  
   I notice that with the flat/flat arrangement of the front rail to bed, 
cinching the blocks 'till they are pulling down hard on the pins will warp 
the middle of the keyframe front rail upward, creating the knock in the mi
ddle instead of on the ends. 
   I prefer the slight crown, and I do mean slight!  
Regards, 
Ed