[pianotech] Downbearing

[Ron Nossaman]

> I am curious about how you would apply this reasoning in the treble 
> section of a RC board.
> If your bridge is set to the apex of the radius cut into the rib, I have 
> found that it is not possible to get the bridge to align with the apex 
> of the radius cut into the top few ribs starting in the upper tenor 
> section(that is unless you want to change this apex rib line 
> dramatically). The bridge will not move straight down when load is 
> applied - moves more at an angle toward the capo .

Away from the capo, actually, if only very slightly.


> Is a bit of guess work needed here to avoid loosing front bearing?

There's some guess work in EVERYTHING about setting bearing, 
so yes. I often make the bridge a bit taller in the treble, 
especially in Steinways, for added stiffness and to get the 
string height more uniform through the tenor/treble. So I can 
set plate height to produce "adequate" (whatever that is) 
front bearing. I also sometimes plane the bottom of the bridge 
at a slight angle in the top section to rotate it back a tad.


> Is is safe enough to plane the bridge in this area based on the sample 
> notches cut when setting bearing (same as the other sections of the 
> piano where this is not an issue) and always end up with positive front 
> bearing?
> Gene

Sure, if planing the bridge cap is how you set bearing. 
There's no reason not to profile the bridge top to accommodate 
what you want. I'm using laminated caps and rib sets that 
don't pre-load like a typical board, so I have to determine 
bridge height before assembly and calculate deflection.
Ron N