Rake Angle, and More

[Farrell]

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I see the point about if the action center is on the string plane and =
the hammer raked so that it is perpendicular to the string plane when =
the hammer tip hits the strings, the hammer tip will move through a =
circular arc steadily going up until it is traveling exactly horizontal =
at the moment it hits the string.

Ahhhhhh, that's it! The hammer tip will not only contact the string when =
it is perpendicular to the string plane, its motion will also be =
perpendicular to the string plane at that moment!

In the case where the hammer butt centers are equidistant from the =
string plane as the hammer bore, and as such the hammers are bored at 90 =
degrees, when that hammer hits the strings, its orientation will be =
perpendicular to the strings, but its motion will be at some downward =
angle toward the strings.

Or am I wrong? Hard to picture in mind accurately. But at least the =
raked hammer travels in the same arc as the shank tip, the right-angled =
hammer travels in a converging arc to the shank tip. To what =
advantage/disadvantage is that?

Thought I had it, but obviously still mixed up.
Terry Farrell
 =20
----- Original Message -----=20
From: "James Ellis" <claviers@onemain.com>
To: <Pianotech@ptg.org>
Sent: Friday, March 14, 2003 8:53 AM
Subject: Rake Angle, and More


> I see that my comments about "rake angle" have stirred up other =
comments
> and arguments.  All I was trying to do was to show you fellows that =
just
> because the hammer is pointed straight toward the string, it does not =
mean
> that it is moving in that direction.
>=20
> Someone sent a jpeg image to illustrate a point.  My computer has jpeg =
as
> well as psp, but that illustration came through as two pages of =
jibberish.
> The system either can't handle it, or else I don't have the right =
version
> of jpeg to read it.  It doesn't matter.  I understood what he was =
talking
> about.
>=20
> I was trying to expose a fallacy, and I think it worked.  I was not
> advocating some crazy impractical design.  Theory and practicality =
often
> don't go hand in hand.
>=20
> A few years ago, many piano technicians believed that a tuning hammer =
with
> a very short head would reduce the bending force on the tuning pin =
despite
> the fact that the head was bored at a very high angle, which elevated =
the
> handle and put the tuner's hand high up in the air.  (I'm using a =
grand
> piano for illustration.)  I saw that I was getting nowhere when I told =
them
> that the very high angle of the handle defeated the effect of the very
> short head, because it put the application of force high up above the
> tuning pin.  So finally I said, "OK, keep raising the angle of the =
handle
> until you have it pointing straight up.  Now, what will that do"?  =
PAUSE -
> PAUSE.  "OH, yeah, now I see it"!  Well, I was not advocating a tuning
> hammer with the handle pointing straight up.  I was using an absurd
> illustration to make a point, and it worked.
>=20
> As long as we have actions where hammers are attached to shanks that =
swing
> in arcs, we will have hammers that do not move straight toward the =
strings.
>  No matter what we do, that hammer is going to be rotating about an =
axis as
> it moves toward the string, and the crown will hit the string a =
somewhat
> glancing blow.  All we are trying to do is to minimize that glancing =
blow.
> Actions have been visualized in people's minds that enable the hammers =
to
> hit the strings straight on, but they are very impractical, so we =
don't go
> there.  We just stay with what is practical, and try to minimize the
> shortcomings.
>=20
> Sincerely, Jim Ellis, RPT
>=20
>=20
> _______________________________________________
> pianotech list info: https://www.moypiano.com/resources/#archives
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