Action Elevations

[Isaac OLEG]

Richard,

 aside the rule that hammer may be hitting the string square, my
believing is that they may hit the strings squarely on forte level,
but this is attained with the flex of the shank, and then the bore is
more probably 1? toward the keyboard.

Anyway the strike point is not the same depending the force of the
blow.

Beside, I have heard that we aim for a shank that is may be parallel
at letoff, that mean it is not when the hammer hit the strings.

if we follow the 2 ideas above, we bore with an open rake as strong as
92 ?
I've find it interesting on small grands to verify the slant of the
strings, from a tonal point of view it helped to try to maintain the
same attack angle.

But I did not go thru the axis height analysis that far, only checked
the geometry of the top action to be workable, so I am not of a big
help there.

I guess that you call the center spread the "attack distance" which is
the difference in height between hammer center and whippen center, I
understand this can be managed and we are not fixed on the 64mm
standard distance, any variation is possible around, strings height
I've been told may not be too high of course, or that distance grows a
lot, aggravating the action internal friction because the "vertical
spread" makes a longer path between parts (seems simple in fact).



P.S Talking about hammer bore I guess that we could take in account
too the fact that the hammer expand a little under first voicing, but
may be too that it will be shorter after some playing.

Cheers

Isaac OLEG

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> -----Message d'origine-----
> De : pianotech-bounces@ptg.org
> [mailto:pianotech-bounces@ptg.org]De la
> part de Richard Brekne
> Envoye : lundi 20 janvier 2003 16:52
> A : PTG
> Objet : Action Elevations
>
>
> Bill, Dave Love, Ron... anyone else who might have insights and
> thoughts...
>
> I've been re-reading Hohfs article of a couple years back and am
> wondering about the problem he sketches relating to the need for the
> string plane to be paralell with the key bed. One of the
> points made is
> that "most actions in common use today are designed to swing the
> hammershank up to the point where it is parallel to the
> keybed" and a
> statement following about the decrease in action efficiency when the
> shank is not paralell to the key bed. In addition we want
> the hammer to
> strike the strings at 90 degrees.
>
> So first... if you have to choose the lesser of two
> evils... what would
> you say is the right choice to make ? Keeping the hammer shank
> centerline parallel to the keybed at strike distance or hitting the
> strings at 90 degrees ?
>
> Course you can alter the rake of the hammer to some degree,
> or even the
> bore distance... but those present other give and takes.
>
> Also... the Jist of Hohfs seires seems really to arrive at
> the optimal
> string height for any given action, with key elevation, hammer bore,
> center spread, and hammershank length as fixed values...
> holy grails as
> it were.
>
> Another question I am wondering about....
>
> If the center spread is to be veiwed as a fixed value, and
> bore distance
> is fixed..doesnt that sort of dictate the height of the
> hammer shank and
> whippen centers over the keybed ?
>
>
> Thanks for your thoughts
>
> RicB
>
>
>
> --
> Richard Brekne
> RPT, N.P.T.F.
> UiB, Bergen, Norway
> mailto:rbrekne@broadpark.no
> http://home.broadpark.no/~rbrekne/ricmain.html
>
>
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