Knuckle Size (was Re: All in a row)

[David Love]

Bill:

I may not have stated my question clearly.  I was wondering about preferred
flange center to knuckle core distance (16mm, 17mm?) that you combine with
.51 key ratio.  Do you have a preference and let the SWR fall where it will
making adjustments by altering the hammer weight?  Or do you vary your
selection of the knuckle radius depending on the overall leverage of the
system and the hammer weight.

The reason I ask is that I have found a trend in combinations of KR and
knuckle radii.  Depending on choice of hammer weight (a factor not to be
glossed over lightly) it would seem that a 16mm knuckle works with KR's up
to .50; 16.5mm up to .52 - .53; 17mm up to .55, 18mm up to .60 or so.  (I
realize that there is also the wippen lever to consider as well which will
change as the KR changes.)

The knuckle radius doesn't seem to really have a place in the Stanwood
formulas:  R = (BW + FW - (KR x WW)) / SW can be manipulated algebraically
to isolate different variables.  But the knuckle radius remains out of the
formula loop except to the extent that it impacts BW and therefore will
change R (Strike weight Ratio).

His formula also does not address distance leverages, that I can see, except
to the extent that a certain range of SWR's will result in acceptable
regulation perimeters.  Do you, when setting up an action, aim for a
particular distance leverage, i.e. a range of dip/blow combinations, force
leverage, or both?  Where do you prefer to take your compromises from?  For
example, if you want to put on a very heavy hammer and don't want to use
assist springs, you can achieve an acceptable front weight within a range of
SWR's.  But depending on the SWR chosen, your regulation specs will vary
somewhat.  Personally, I try to set my FW's below maximum by 10-15%, and
select KR/knuckle radius combinations that give me a .390 - .400 key dip
with normal blow distance.  The resulting SWR will dictate the SW zone.
It's not always possible to do that, sometimes the hammer of choice forces a
compromise somewhere.  Maybe the more precise question is do you find that
SWR always has a direct relationship to distance leverage and, if so, is
there a preferred SWR?

Any comments?

David Stanwood, if you're listening, I would love to hear your comments too.

David Love

----- Original Message -----
From: "Bill Ballard" <yardbird@pop.vermontel.net>
To: <pianotech@ptg.org>
Sent: November 11, 2001 8:11 AM
Subject: Knuckle Size (was Re: All in a row)


> At 11:44 PM -0800 11/10/01, David Love wrote:
> >Bill:
> >
> >Do you have a knuckle radius that you prefer to combine with that key
ratio,
> >or do you vary it aiming instead for a particular SWR range?
>
> In general, I prefer a larger diameter knuckle on the assumption that
> a smaller diameter presents a steeper curve to a jack sliding out
> from under it, thus compressing the feeling of escapement into a
> smaller portion of the keystrokes arc. Escapement is enough of an
> obstacle to ppp playing. Frequently it determines the bottom end of
> the dynamic range. I'd like to keep it at a minimum.
>
> That being said, an extra mm of knuckle diameter can rob whatever
> advantage you may gain in the knuckle mounting distance. But I'll buy
> that in the larger knuckle diameter and pay for it at the key ratio.
> It all comes out in the wash. Regardless of what leverages inside the
> lever train yield a 5.5 SWR (beit a 25mm knuckle mounting distance or
> a .40 key ratio <g>), this overall SWR will dictate the dip.
>
> Bill Ballard RPT
> NH Chapter, P.T.G.
>
> "I go, two plus like, three is pretty much totally five. Whatever"
>      ...........The new math
> +++++++++++++++++++++