pinning bridges

[Delwin D Fandrich]

Ron Nossaman wrote:

> .... 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'.

Yamaha is not the only piano builder who has used -- still uses? -- this method
of bridge drilling.  It may be the least noticeable, visually, but this is
already an awkward portion of the scale.  Why make life more difficult than it
already is?  There is really no need to use this 'solution.'


> 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.

The bridge pin spread (your 'black') can be varied without noticeable tonal or
structural consequences as long as the string deflection angles stay within
reason.  In my work I like to see that deflection angle fall between 10º and
12º.  Obviously, as the back row of bridge pins is brought closer to the front
row -- decreasing the spread -- this angle will increase unless some
compensation is made by offsetting them slightly.

> 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.

This is easily done if the bridge is being hand drilled.  It is somewhat harder
to do if the bridge is being drilled and pinned by automatic machinery.  It
requires another level of sophistication in the machine doing the work.  Again,
it is not usually necessary.


> 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.

In my view, at least, this consideration would be well down on the list in terms
of locating plate struts.  It is far easier to float the pin spread by varying
the spacing between the front row and the back row of pins.  As long as there is
adequate compensation made for the string deflection angle by offsetting the
back row of pins slightly, there is really no major drawback to this solution.
It's clean and simple.

Del