C88 Hammer Position/SPR

[Delwin D Fandrich]

----- Original Message -----
From: "Overs Pianos" <sec@overspianos.com.au>
To: <pianotech@ptg.org>
Sent: November 13, 2001 2:30 PM
Subject: Re: C88 Hammer Position/SPR


> Del, Tony et al,
>
> >. . . Early writers spoke of
> >a SPR at C-88 of between 1/12th up to 1/20th of the speaking length. If
> >memory serves, Wolfenden mentioned a SPR of 1/16th in the first edition
of
> >his book.
>
> Yes, I am starting to suspect that the radius and the hardness of the
> bar may have an influence over the ideal SPR. We have done quite
> careful checks to arrive at the optimum SPR at C88 for the three 225
> we've built so far. It's turned out for all three instruments that
> with a speaking length of 53 mm, the ideal strike point from the capo
> was 2.5 to 2.75 mm (1/19 - 1/21). Now I realise that this seems to be
> rediculously close, but I suspect that the small radius hard bars we
> use just might allow for more flexibility of the string at the
> termination point - hence the requirement for the hammer to come
> closer to the bar. It's just a hunch, but I suspect that a larger
> radius bar might in some way limit the ability of the string to be
> excited. What do you think Del?

I'm wondering how you managed to pinpoint the actual mass and/or shape
centerline of the hammer that precisely. I'm also wondering how you managed
to control hammer and hammershank whip on impact enough to be sure that is
really where the hammer is striking.

You are right that the radius of the V-bar will affect the hammer strike
point. I've no idea about how the hardness might change things--I've never
looked into it that way.

Yes, that does seem a bit close to me. But the difference between a SPR of
1/20th and 1/14th is about 1 mm. Pretty hard to tell the difference with a
real-life hammer and hammershank. And one that is easily accomodated by
sliding the action in or out just a bit.


>
> How's your new piano coming along Del?

Slowly, oh so slowly.

Del