chisels over to bridge height

[RicB]

Hi Terry

Thanks for the answer on this.  I got another answer just today from a 
friend in Danmark who says Bosendorfers do their bridges this way.  The 
bridge is fixed on the panel, soundboard temporarily screwed down and 
its placement indexed, and then one runs a thin string... fishing line.. 
whatever... from the middle string hole in the agraffe to the middle 
hitch pin, usually for each A on the long bridge... or something like 
that.  Then a chisel is use to make a cut like a notch edge back to 
where the notch will be.  The wire (fishing line) is then run through  
to gauge the bridge height and one planes down to the desired height and 
angle.  The string in this scheme should leave the back of the bridge 
and make no angle downwards to the hitch pin so you dont need to worry 
about doing the same thing on the back side of the bridge.  Seems easy 
and sensible enough. 

So.... problem solved.  I'm just waiting for the final scale figures 
from a designer over here before proceeding.  The trick with the rib 
notches and epoxy putty works great... btw.  Poifict fit as it twere.

Cheers
RicB


    Terry Farrell volunteered:

    Interesting question. And it would become more of an issue as the
    backscale
    and speaking length decrease - as you say, in the high treble.

    I do my downbearing adjustments prior to installing the cap. I make
    little
    blocks of wood the same thickness as my cap, and I make them as wide
    as the
    front-to-rear bridge pin spacing will be. I then plane down my
    bridge root
    to whatever height I need so that after cap installation, I have my
    desired
    downbearing. That eliminates the concern you have with your situation.

    But you likely have your cap glued on already.

    You could get your high school trig book out and calculate the
    amount of
    apparent increased downbearing you would need in order to result in the
    lesser desired downbearing after notching.

    Or maybe the difference is so small that folks don't really worry
    about it?

    Could this be part of building pianos, each of which has its own
    personality?

    Terry Farrell

        ----- Original Message -----
         > I cant say what a wealth of information this thread has
        yielded.  I hope I
         > might trouble you all for one more piece of advice.  I'm just
        about ready
         > to lay out my pattern and drill bridge holes.  I did a very
        nice job of
         > fitting the bottom contour of the long bridge to the
        curvature of the
         > soundboard, which is temporarilly fixed by clamps to the rim
        to simulate
         > its glued state.  And I find that I need to bring down the
        bridge surface
         > in order to get the kind of downbearing angles I need.  The
        question I
         > have is that in an un-notched state... the bridge will
        present a height at
         > the leading edge then otherwise... particularly noticeable in
        the high
         > treble.
         >
         > So... how does one account for and deal with this when
        planning down the
         > bridge surface for desired string deflection ?
         >
         > Thanks again
         >
         > RicB
         >