[CAUT] Jack speed, (was Tight balancier

[Fred Sturm]

    Lots of food for thought in this subject matter, or range of subject
matter. On the question of jack pinning, and thinking of the high speed
video, the one thing I am sure of is that we don't really know how much
effect relative jack pinning friction has on that "jack bounce." I hope that
maybe our good friend Steven Birkett will want to examine this parameter.
For the time being, I think that jack bounce illustrated in the Kawai videos
is best controlled by a limiting factor: felt in the balancier window. Next
in order of effect would be minimizing aftertouch. And only then, IMHO,
would come pinning, assuming it isn't ridiculously loose (zero measured
friction).
    On the subject of pinning friction, I have a couple questions for those
who are talking about 6 - 8 grams for balanciers and/or jacks. So we are on
the same page, what precise methodology are you using to measure? I assume
parts are in a horizontal position. Is measurement at a "standard" one inch
distance from center? How are you eliminating the spring from the picture?
When I try to take that measurement, I find I could sure use another hand,
and am wondering if some of you have come up with a convenient way to hold
the spring out of the way without unduly affecting its tension.
    We are talking for the most part about Steinways here, in a practical
sense (they are most of our concert instruments), and here the modern
Steinway bushing, teflon impregnated felt, comes into play. I haven't had
enough experience to come to firm conclusions about these centers, having
had much more experience with verdegris, teflon, Tokiwa, and Renner parts in
these beasts. And each has its own quirks. But the current production
bushings are a queer duck, based on what experience I have had.
    I decided to re-pin the hammer flanges of our new D after we had had it
a couple years (it's now 6 uears old), because I thought at the time that
the pinning was way too loose based on experience with other styles. Mostly
1 - 2 grams resistance. So I started out, expecting to increase by a half
size, with minimal burnishing, and occasionally a wee bit of reaming. I
found, however, that when I inserted that half size larger pin, it was way
too tight, and required a good bit of reaming to get down to 4 - 6 gm. So
the next flange, after inserting the larger pin and feeling it was again way
too tight, I tried the original size pin. It felt about right. Installed, it
produced 4 gm or so, and swings to match. I experimented for a while,
carefully checking friction before un-pinning, measuring each pin I took
out, going through those same steps. And for the most part, this sequence
repeated itself: original pin, being removed and replaced, resulted in 1 - 2
gm rising to 4 or so gm. Then I went back to my earlier flanges, and, lo and
behold, they were back to 1 - 2 gm. Bizarre, no?
    About this time there was considerable discussion of these bushings on
this list, with Don Mannino weighing in about firmness being much more
important that any friction parameter. I started looking at it from that
point of view, and decided to leave well enough alone, especially as the
Steinway folks were saying 1 - 3 was their target. I provisionally changed
my mindset, and found I could live with regulating and prepping with that
friction parameter.
    So I am wondering what others of you who have had more experience with
these bushings have been finding. Ed Foote recently noted that he was
pinning jacks to 6 gm or so, but they got looser soon after. Is this maybe
just the nature of this beast, that within fairly close parameters these
centers are slick enough that friction will just want to go down to 1 - 3?
Regards,
Fred Sturm
University of New Mexico

 
On 11/11/06 12:43 PM, "A440A at aol.com" <A440A at aol.com> wrote:

> Jim writes: 
> << I don't
> think I can add much to what has already been said, except for one thing.
> I don't remember who said it, or when, but it had to do with pinning the
> jack as tightly as the balancier.  I don't agree with that.  You are far
> more likely to have repetition problems due to a jack that's too tight than
> you are with one that's too lose. >>
> 
> Greetings, 
> Um, That was me that said that!  I have found that an action will play just
> as fast with a jack pinned at 6 grams as a jack pinned at zero friction.  The
> jack pinning doesn't seem to interfere with repetition until it passes 8
> grams, and even so, you have to have somebody that can play real fast to
> create a 
> problem.
>   A 6 grams, a jack will still move faster than the eye can see.  For heavy
> use pianos, the pinning will loosen up from where it begins, so I have always
> pinned them near 6 grams and never had a problem with repetition speed. The
> jack will move faster than it needs to, even with 6 grams of tension. (Alicia
> de La Roccha played Ravel on a piano I had set up with jacks pinned like this,
> and told the stage manager it was the first time she had ever found a piano
> that needed nothing but tuning.)
>   Many techs think that looser pinning and/or stronger springs will
> increase repetition speed, but I disagree.  Repetition speed depends primarily
> on how 
> fast the key returns and checking height.  The jack reset speed of an a
> spring set to throw the hammer off the balancier will not exceed that of one
> that 
> has a so slow of a hammer rise that it cannot be felt in the key.  If you
> compare return speeds of two adjacent keys, one with a lot of spring, the
> other 
> with much less, you will see that both come up together.  The problems with
> heavy 
> springs are found in pianissimo playing, where the resistance to escapement
> is higher due to the drop button interfering at the last possible moment of
> control.  
>   The near instant empirical capacity of this list is such that if we
> wanted, there could be a hundred different techs try the tighter jack pinning
> and 
> publicize their findings in the next couple of days.  I certainly don't think
> everybody should believe what any one of us says!  Try a tighter jack for
> yourself and see if you can play it fast enough to fail, let us know what you
> find. 
> 
> Regards,  
> 
> Ed Foote RPT 
> http://www.uk-piano.org/edfoote/index.html
> www.uk-piano.org/edfoote/well_tempered_piano.html
> 
>