pinning bridges

[Ron Nossaman]

Hi gang, a few more harmless observations and speculations for your general
entertainment, enlightenment, discussion, annoyance, or trash can.

For some time now I have been looking at how different manufacturers notch
bridges and install bridge pins. (Yea, I know, but I need *something*
interesting to do while I'm tuning) Making new bass bridges for verticals is
simple and nearly goof proof. Recapping treble bridges in grands is
considerably more involved, but *most* folks work from a pattern made from
the old bridge and try to reproduce what was there originally. How about if
you are designing a scale and making a treble bridge from scratch? 

At a certain point in the treble scale, somewhere around the beginning of
octave 5, give or take depending on the length of the scale (the longer the
piano, the higher in the scale this should occur, yes?), the back bridge
pins of a given note, say C5 (52), will intersect the front pins of B5 (51)
somewhere below the bridge surface unless something is repositioned. There
seems to be four ways around this.

1. Scaling: This involves foreshortening the speaking lengths of the scale
(coming down from the treble) just enough to maintain pin clearance through
the 'crossover point', and jumping back to the natural (I assume) length
progression at the change in wire size. The 'benefit' here seems to be that
the distance between the front and back rows of bridge pins can remain
constant through the scale, possibly to simplify automated drilling
procedures. Yamaha does this in some models. Oddly enough, this is probably
the least noticeable (visually) of the various compromises. BTW, to minimize
typing trauma, and since Merle didn't supply me with an official name for
it, I will call this distance the 'black'. 

2. Floating the 'black': Leaving the scale progression alone, the black can
be progressively lengthened from about three unisons up scale, down to the
'crossover' point, shortened enough for clearance at that point, and blended
back into the 'standard' length a couple of unisons down scale. This is a
very common way of dealing with, not only bridge pin interference, but
fitting the scale on the bridge at scale breaks where the bridge dog leg
isn't severe enough to center the 'black'. Some pretty severe examples of
this can be seen in some models of Baldwin and Steinway, but it is a widely
practiced and very common technique. Quite noticeable, especially if the
back row of pins isn't offset correctly and the stagger angle increases
severely as the 'black' narrows. 

3. Aiming the pins: When the builder feels the pin placement is where it has
to be, and no further relocation compromise is desirable, or possible, All
that is left to do is modify the fore and aft (not the side) drilling angle
to make clearance where none exists. This is a very common technique, and
when found in tandem with #2, results in that charming snaggle toothed
bridge look we all know and love so well. noticeable to the point of
screaming at you from across the room if over done.

4. Getting lucky: If the crossover point coincides with a plate strut,
option #1 could be used with no visible indication that any compromise was
made. I don't know how much leeway a designer has on placement of plate
struts, or if they even normally consider such things. Invisible, but I'd
like to see the tension and inharmonicity curves.


That's it, mostly. Sorry if it reads like a lecture, it wasn't intended to,
but I didn't see any graceful way to get it into a discussion type format
so... Any comments, observations, dissention, flushing sounds?

PS: Has anyone got a Yamaha (or any other) scale (speaking lengths as well
as wire sizes) exhibiting method #1. I'd like to lay it into a scaling
program and see how everything fits. 

Back to work,
 Ron