chisels over to bridge height

[Gene Nelson]

I am curious if part of the indexing could include locating the speaking 
length for the sample notes? Otherwise how would one know where the notch 
will be - or maybe just close enough is ok? I would think that notching 
about 1mm or so from where the bridge pins will be drilled may be 
advantageous for later finish notching and will not matter that much to the 
bearing?
Thanks for any thoughts.
Gene Nelson
----- Original Message ----- 
From: "RicB" <ricb at pianostemmer.no>
To: <pianotech at ptg.org>
Sent: Monday, March 19, 2007 12:43 PM
Subject: chisels over to bridge height


> 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
>         >
>
>
>