back check, a magical mystery tour.

[Isaac OLEG]

While... I don't see how chalking the tail of the hammer can show us
anything as the chalk will depose on the backchecks in any case during
the checking.

I believe the usual method to check clearance and security is good
enough (and even very secure if on use a bit more force). this said
The hammer rubbing on the check is felt while playing the note (once
we are suspecting it or if we compare with a corrected regulated one).

But indeed the 2 mm rule is certainly also a security measure by some
aspect.

Then, let's say also that different type of tails and bachecks may be
addressed differently, that is why it seem important to me to
understand the basic concept underlying the process.



best Regards.

Isaac



-----Message d'origine-----
De : pianotech-bounces@ptg.org [mailto:pianotech-bounces@ptg.org]De la
part de Richard Brekne
Envoyé : mercredi 18 août 2004 19:06
À : Pianotech
Objet : Re: back check, a magical mystery tour.


Grin... Stephen... this is the second time in a row you struck the
exact
chord that brings an appreciative smile to my innards... :)  This time
its directing us towards the obvious... common sense as it were.  This
explanation doesnt have a lot of sensuality to it... but it does show
some promise of being in the right ball park.

Stephen Birkett wrote:

> We've seen quite a few 'second-tier' hypotheses - as Ric says, sexy
> explanations - for the backcheck phenomenon. These things obviously
> need to be examined experimentally, but a small dose of Occam might
be
> a good thing first. I'm thinking something is causing this that
occurs
> before the string impact. The obvious candidate is interaction
between
> the backcheck and the hammer tail as the hammer heads toward the
> string. Backcheck clearance is supposed to be pretty tight, and I've
> seen enough examples of slight catching on the check  as the tail
goes
> up, enough that power is lost without it being obvious. For a given
> action configuration, this effect doesn't occur for all blows. It's
a
> function of various action parameters, including softness of the
> whippen cushion and other felt contacts, hammer shank flexibility,
> tail geometry, and so on, as well as the type of touch applied to
the
> key. Lowering the check to achieve the magic 2mm separation may very
> well ensure adequate clearance in all cases.
>
It may very well indeed... especially when the other back check
parameters are adjusted correctly.

> It's probably possible to check this on a "dud" key before and after
> making the adjustment of backcheck height, even with just a bit of
> chalk on tip of the key tail. Static clearance of the check/key tail
> is certainly no guarantee of dynamic clearance. If it's too subtle
for
> chalk it will need some targeted experiments with high speed images
to
> investigate properly.
>
A good suggestion.. and easy to carry out... most certainly at least
some what revealing. I'm a gonna give this one a try :)

> From the current discussion, it seems the effect is also apparent if
> backcheck clearance height is too much more than 2mm, and the
> explanation above doesn't address that of course.  To those who've
had
> good results with Andre's technique (including Andre himself), in
> practical circumstances how often do the checks have to be lowered
vs
> raised?
>
Well.. lets see...if the back check is too high or too low.. then it
has
to be moved in the lateral direction and its angle has to be changed
to
maintain the same <<static>> check height and holding strength.  So
maybe.... the 2 mm simply describes the optimum distance for these
other
two directions to also be at their most efficient ??

As far as how often checks need adjusting.  Hmm... you'd be suprised
how
varied back check height is off the factory line... even in pianos
like
Yamaha where <<precision machines>> are specially made to do the job.
Then there is the hammer change job done by the tech down the
street...... grin..  In short...  it happens often enough that they
need
addressing.

> Stephen

Cheers
RicB
_______________________________________________
pianotech list info: https://www.moypiano.com/resources/#archives