[pianotech] Downbearing

[Ron Nossaman]

> Hi Ron:
> 
> As the practical man we all know you to be (and I think it is of real value
> for you to occasionally bring us out of the clouds with your nuts and bolts
> perspective, thank you very much!), what steps do you take in practice to
> insure that the front and back bearing angles are roughly equal?  Since you
> are usually installing a new soundboard (and presumably a new pinblock),
> where in the combined processes do you make adjustments that will at least
> get you roughly in the ballpark of where you want to be?
> 
> Will Truitt 


It's very mystic. Get yourself some Henbane, a small round 
rock, and a toad... No, wait, that's something else. Ok, 
here's the deal. A bridge with the top parallel to the bottom, 
strangely as if it had passed through a planer, sitting more 
or less centered on a line of crowned ribs, will make the 
bridge top close to parallel to a line from agraffe to hitch, 
which will get you positive bearing on both front and back of 
the bridge. Where the comparison of these angles ends up 
depends on the final net downbearing angle, and how much it 
has deflected the board.
Ron N