Tuning Duplex

[Delwin D Fandrich]

----- Original Message -----
From: "John Delacour" <JD@Pianomaker.co.uk>
To: <pianotech@ptg.org>
Sent: November 15, 2001 1:02 PM
Subject: Re: Tuning Duplex


>
> There's nothing "one-of-a-kind" about string plates and provided the
> pattern is accurate then the horizontal relations between points will
> be identical in every casting.  The only variation possible is in the
> thickness of the casting owing to variations in the closing of the
> boxes and quality control would reject any castings beyond certain
> tolerances.

This is amost correct. The V-bar is in the cope (the upper part of the mold)
and this does tend to shift around just a bit from one casting to the next.
Especially as the mold starts to show signs of wear. This is just one reason
I prefer a separate V-bar that can be placed under the capt tastro bar by
the manufacturer.

I'm sure, John, you are able to work with only the finest of piano
manufacturers, and those are the ones who actually stick a plate up on a
granite flat and check one once in a while to be sure they are adhering to
some reasonable tolerances and specifications. The rest of them, however,
pretty much take plates the way they come from the foundry and make them
fit. I've been in enough factories--and worked with enough manufacturers--to
know that, while this practice is not universal, it is far more common than
we would like to think. And, yes, I'm including the makers of some so-called
very high-end instruments. Patterns do change over the years; repairs are
made--and not always correctly--and unintended changes do creep in unless
the manufacturer is ever diligent. Few were, though I think improvements are
being made by many. The realization is finally getting in there that true
quality control is really more economical than constantly struggling to make
things fit.


>
> As to long bridge placement and notching, what variation have you
> actually detected and recorded, as opposed to merely presuming?

I don't know about others but, yes, I have personally observed both long and
short bridges being placed in the wrong place. I have also personally
measured substantially more than minute discrepancies in the fixed
relationship between the (cast-in) front duplex bearing bars and the
speaking length of the string.

Del