[pianotech] action ratio

[David Love]

The problem, as far as the formula is concerned, is that the .040, .050,
.060 do not comport with the formula requirements (I assume the equality was
based on something).  And your point is suggestive of the fact that the bit
of key travel is not really the critical factor.  Rather, it is jack
clearance from some yet unknown starting point.  So aftertouch for the sake
of that formula may be something other than what we think of as it relates
to the thickness of the cardboard placed underneath the key.  That's the
main point of the question.

 

Regarding ideal specs and action ratios (let's put aside for the moment that
the method of determining the ratio is something of a debate), there is no
getting around the fact that a certain action ratio will tend to produce a
particular regulation or combination of dip and blow, all other things being
equal, i.e. let-off, aftertouch, jack position, knuckle diameter, capstan
angle perhaps.).  If your ideal is 45 mm with .390" dip  (or 9.9 mm to keep
the units the same), then you will only get that regulation with a
particularly action ratio.  You won't get that with 5.0 and you won't get
that with 6.5 unless you alter the let-off or the aftertouch and at both
extremes that is likely going to be detrimental.  

 

Now I think that 9.9 mm dip, or let's just say 10 mm for ease here, and 45
mm of blow is a good target.  So my question is, in your experience, what
action ratio is most likely to produce that without any fudging and further,
what standard of cardboard punching thickness key travel are you using,
ideally anyway.

David Love

www.davidlovepianos.com

 

From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of Dale Erwin
Sent: Sunday, August 26, 2012 7:32 PM
To: pianotech at ptg.org
Subject: Re: [pianotech] action ratio

 

Last Sat. Laroy Edwards and I taught a joint class in my shop to members of
several local chapters in the region. Great fun and the Head piano Meister
at 84 yrs young; ... was on his game. 

  I had the pleasure of sitting in his "after touch class". where He clearly
defined after touch. 

 

  Short story is that after touch begins as soon as the jack escapes the
knuckle. How far it moves past that is the real after touch
number/distance/feel. One limiting factor to jack movement and hence after
touch is determined by the total length of the repetition lever slot. The
jack cannot move beyond the rep.lever slot stop with out the jack tender
binding and then breaking off. Bummer. Ca glue please anybody.

 

  Another limiting factor is that the jack must escape enough that it DOES
NOT have opportunity to dance with the knuckle and do the mister booble head
thing. With repetition in mind the farther the jack escapes the farther it
has to travel back, and we all know this of course will slow repetition.

 

   So within those  parameters in mind some variability is
allowed/acceptable based on subjective feel. I'll leave it at that for now.
Using Davids cardboard method to just sense jack escapement is quite good I
think.  Many techs that use this method state a preference like..... "I like
.040....050 ...060. cardboard placed on top of the front punching as there
sensory gauge" 

 So these are small parameters to be sure but we and our pianists clients
live in the realm of the subjective. Some like dip/key travel deep some like
it so short that mister bobble head can almost dance and these folks, oddly
enough....have learned to control it.

 

 Dip.

  This Sticky wicket wording to me always needs clarification

   So this means to me overall key travel top to bottom. How we measure it
will be confusing unless we speak specifically how we do that. In setting up
any action regulation parameters I am  looking for roughly those numbers
David suggests. ie. 45mm or 1 3/4 blow....Let off at approx. .050/1.3mm,  

(I like it close.) and a .390 dip.  I measure that just in front of the key
pin & right under where the finger touches the key much of the time with a
direct measurement gauge. (the Erwin dip gauge)

 ( see picture.)  Now I realize that the key travel depth can vary given the
wide variance of action ratios, typically 5 to 6.5, but actions that fall
within what we all refer to as normal compliance, fall into these numbers
routinely. So its at least a starting point when looking for parameters.

Other folks measure at the very front of the key with a metric ruler.
Whatever works

 

 Another consideration is that the standard green front rail punching
available can easily squish .035. 

That seems like a lot don't ya think? This is not a promotional but the
fairly new Cresendo punching compress a very predictable .015. So,.... over
all key travel can be set very precisely. Some don't like the feel but
that's another story. So overall dip/key travel set from a basically static
method changes quite variably under different dynamic ranges/key pressures
with the green squishy punching. 

 So now;... what is the dip really?

  I just wanted to clarify some other reasons why Jim might be a bit
confused since I was thinking about it lately.

  

 

Dale Erwin R.P.T.
Erwin's Piano Restoration Inc.
Mason & Hamlin/Steinway/U.S. pianos
www.Erwinspiano.com
Phone: 209-577-8397

 
  

 

-----Original Message-----
From: David Love <davidlovepianos at comcast.net>
To: pianotech <pianotech at ptg.org>
Sent: Sun, Aug 26, 2012 11:51 am
Subject: Re: [pianotech] action ratio

I don't quite think it's apples to oranges because for any given action
ratio there will be at least a limitation to the regulation specs or the
dip/blow relationship.  I agree that the formula is confusing but I don't
think it has to be.  Determining when let-off and aftertouch actually start
seems to be the problem.  Once established, however, I see no reason why a
default setting for the sake of this formula can't be used.  Moreover, I
find that it's the aftertouch part that is confusing.  As far as the formula
goes, my own experience suggests that a let-off number of 1.5 and an
aftertouch number of 2.5 produces regulation specs that I expect to find
with a given action ratio.  The problem seems to be defining exactly what
aftertouch is, at least as it pertains to this formula.  Blow, dip and
let-off are more easily defined.   
 
David Love
www.davidlovepianos.com
 
 
-----Original Message-----
From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org
<mailto:pianotech-bounces at ptg.org?> ] On Behalf
Of Jim Ialeggio
Sent: Sunday, August 26, 2012 8:32 AM
To: pianotech at ptg.org
Subject: [pianotech] action ratio
 
David L said:
 
<The question at hand has to do with what exactly is the after touch spec
that's used to make the formula ratio by product of the levers equal to the
blow/dip ratio as given.
(and)
<But when I input those numbers in this calculator, as you can see, then by
that formula a 5.75 AR with 45 mm of blow distance should regulate with 8.6
mm of dip.
 
This illustrates the confusion I find in these formulas, if they are to be
used from a design perspective rather than as a ballpark reactive position
in the field. I feel the (blow distance-let off)/key
dip-aftertouch) part of the equation, when compared to the lever arms part
of the equation is apples to oranges.
 
The lever arm side of the equation looks at the lever arms as the product of
fixed ratios.  However, the blow distance ratio does not look at blow
distance and key dip as fixed ratios, but rather inputs arbitrary
letoff/aftertouch as necessary to make that side of the equation match the
fixed ratio side, as I think you've noted, David.  Or seen another way, if
you are going to use the blow distance side of the equation as given, then
the lever arm side must take into consideration the whip's changing leverage
and the shank's changing leverage during letoff. This changing leverage
presents difficulties that would require computing complexities way beyond
simple algebra.
 
Taken in this light, your shy 8.6mm dip could be more a result of blow being
quantified artificially.  According to the fixed leverages, blow is not the
distance between hammer at rest and the strings minus letoff, but rather
(Full unimpeded travel of the hammer with out any letoff or
strings) = Action ratio*(key dip-aftertouch).
 
By the way, my comment here is not that this formula doesn't empirically
work, but rather that the thinking behind it seems to be selective and thus
confusing, at least to me.
 
Jim Ialeggio
 
 
 
 
-- 
Jim Ialeggio   
jim at grandpianosolutions.com
978 425-9026
Shirley Center, MA
 
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