Will
The only way to tidy up the pivot point on any balance rail would be to cut the front edge of each punching. Come to think of it, wouldn't the accelerated action bearings be a superior idea considering the above stated premise?
Dale
-----Original Message-----
From: William Truitt <surfdog at metrocast.net>
To: pianotech at ptg.org
Sent: Wed, Jan 20, 2010 3:38 am
Subject: Re: [pianotech] Action Ratios Recap - non-ideal approach
Hi JD:
>"The key pivot centre is not precisely at the balance pin centre;
rather it pivots about a centre which moves towards the front edge
of the key balance felt punching as the key is depressed. This
causes a change on the ratio of the key-capstan pair.
Not on a piano with a properly designed balance rail. Some balance
ails are quite obviously properly designed, and others are better
esigned than they appear at first glance, for example the Steinway."
Could you expand on this, please? As in how you go about determining how it
s properly designed and avoids the movement of the pivot point towards the
ront of the balance rail punching. Any other comments in addition would be
ppreciated also. Thanks.
Will Truitt
----Original Message-----
rom: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
f John Delacour
ent: Monday, January 18, 2010 8:49 PM
o: pianotech at ptg.org
ubject: Re: [pianotech] Action Ratios Recap - non-ideal approach
At 16:22 -0800 18/1/10, peter sharp wrote:
>I have been reading, with interest, some of the PTG email regarding
deriving the action ratios.
One or two comments on your posting:
>In order to set up the piano action correctly, for touch, the hammer
travel distance, as hammer blow, is regulated to fit the given dip
at the front of the key. For any given piano, there is little choice
about how much blow to set, once the dip is determined.
This assumes that you have a "given dip". I always regulate the blow
nd set-off first, so that is the given. I then regulate the key dip
o achieve the proper escapement.
>There is some choice with aftertouch, and the technician looks for
this in ensuring the jack has sufficient clearance from the knuckle.
Pianists may also ask for a "softer" and "closer" aftertouch.
Pianists should be discouraged!
>Secondly, the hammer letoff must allow for escapement whilst at the
same time give control at all dynamics; for the pianist, a close
letoff will give nice control for pianissimo, but for the
technician, it may lead to double-striking or bobbing of the hammer.
Again, there is some small choice with let-off.
Close set-off will not lead to burbling if the escapement, the spring
ension, the check angle, the hammer tail etc. are properly regulated.
>The response of the hammer to the key travel is non-linear; that is
to say, the ratio of displacements (also called the velocity ratio)
varies as the key is depressed. This is because the internal ratios
of the action components vary as they move.
Certainly, but the precise ratio can be calculated at any point.
>The key pivot centre is not precisely at the balance pin centre;
rather it pivots about a centre which moves towards the front edge
of the key balance felt punching as the key is depressed. This
causes a change on the ratio of the key-capstan pair.
Not on a piano with a properly designed balance rail. Some balance
ails are quite obviously properly designed, and others are better
esigned than they appear at first glance, for example the Steinway.
>The capstan, in turn, slides across the whippen heel, so that the
velocity ratio varies for this capstan-jack pair. We can regard the
jack to whippen pair as non-variable, and does not need to be
considered as an additional pair here.
In a properly designed and set up piano the capstan does _not_
slide" across the lever heel; they roll round each other as two
inions. The slippage is so slight as to be almost completely
egligible over the whole range of the motion, even if there is a
light deviation from the designed set-up. The velocity ratio does
ndeed vary, but not for this reason. The capstan is on a path of
ecreasing ascent while the lever heel is on a path of increasing
scent for a given angular velocity, and the arcs are of different
adii. That is the reason.
The jack-to-knuckle contact point varies as the jack slides (rolls)
across the knuckle as the hammer lifts, and changes the velocity
ratio across this pair.
Here, yes. But the same considerations apply in addition.
>With these three pairs of varying component ratios within the
action, a simple multiplication of the three ratios to give a number
consistent with the overall velocity ratio is not so easy; this is
due to the difficulty of determining exactly which ratio we should
use for each pair.
It is also difficult to eat soup with a fork. Use a spoon and the
ifficulty vanishes.
>...Using dial gauges is useful, but becomes tedious when working in
the real world.
The measurements necessary for proper and precise action set-up are
imple and can be made with a millimetre rule. Precision
easurements might tell you something is wrong but they won't tell
ou how to put it right.
>The point here is that to try to derive this result theoretically,
by assuming certain positions for lever centres and points of
contact, is fraught with frustration, unless you recognise that the
ideal calculations must be modified by the non-ideal behaviour of
components turning on wool and leather about movable rotation
centres. And theoretical ratios can only be taken at one position,
being at letoff.
As I've said above, the precise ratios can be calculated at any
osition of the key. There is nothing "ideal" or "theoretical" about
hese calculations and the wool and leather have nothing to do with
t. If the "moveable rotation centres" were random points, then sure
t would be tricky, but they are precisely defined at every moment.
>All of this recognises that the action component ratios, within each
of the three pairs, are themselves able to be modified to give
different responses within the same overall action ratio. But that's
another story.
No, that is THE story.
JD
--
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