[pianotech] Action Geometry [was Action Ratios Recap]

[William Truitt]

To Nick and John:

My compliments to both of you for your fine use of language as well as the
benefit of the knowledge imparted to us.

For too many, language and words are a lost art, with no awareness of the
pleasure that a delicious phrase can bring as it rolls off the tongue, or
the repartee of the exchange between two friendly adversaries.  Clearly,
neither of you have forgotten.

Thanks for putting a smile on my face.

Will Truitt  

-----Original Message-----
From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of John Delacour
Sent: Friday, January 15, 2010 3:42 PM
To: pianotech at ptg.org
Subject: Re: [pianotech] Action Geometry [was Action Ratios Recap]

At 11:12 -0700 15/1/10, Nick Gravagne wrote:

>..."Methinks, Horatio, when truth be false, the consequence worse!
>Whence ratio, Horatio, to me 'tis but lever; to others still I am found
>but too clever."

You had me fooled - brilliant!

Thank you, Nick, for your considered and witty response.


>Perhaps the reason that "nobody has even commented on" your Jan 10th
>post is because, as I see it, it is not complete, except for the
>rationale and mathematics of capstan rise to that of key dip.

Quite so -- it wasn't meant to be complete but merely to present in 
detail the calculation of the first ratio in the chain, to show the 
method that is applied to all the subsequent calculations, which get 
rather more involved.  A full presentation would have overtaxed the 
brain of the writer and the eyes of the departing readers.

>...Your palpable criticism of Pfeiffer's work and, presumably, any modern
>technician's work who borrows from him has, I am guessing, not gone
>unnoticed.

I've had Pfeiffer's books for over 30 years and they have been an 
invaluable source of information and inspiration to me.  I recommend 
them to anybody.  That does not mean that I accept all his 
conclusions... but enough of that.

>You are entitled, don't get me wrong. I have not ignored your post, but
>there is much to consider. Your argument that the most exacting ratio of
>key dip to hammer rise, as these relate to x and y positions of
>components gliding along arcs, is, of course, completely valid. What
>remains to be seen is what we gain from such exactitude.

As I've said before, I see no point in approximations when by using 
simple school geometry/trigonometry one can achieve precise results. 
That doesn't mean that every technician needs to polish up, or more 
likely learn from scratch, the necessary mathematics, but by feeding 
a number of measurements into a computer programme it is would be 
possible for him/her to get all the information he needs about the 
behaviour of the action and see the results of any planned 
modifications.  This includes the production of precise scale 
drawings and even movies.

>I have long thought that we yet lack a consistent and unified approach
>to the subject. I recently evaluated a Young Chang action by physically
>measuring the lever arms using three different methods, resulting in
>three different ARs of 5.9, 5.7 and 4.6. The AR that mostly agrees to
>the actual measurement (a bit tricky to do) of dip and subsequent hammer
>rise is the 5.7 AR.

As you say, certain measurements are frustratingly difficult to get 
exact.  I'd guess that the proper ratio would be 1:5 (and here 
Pfeiffer would agree!) and that anything much different would be due 
to poor set-up by Young Chang, the wrong roller size, the wrong 
roller position or the wrong key ratio -- but that goes without 
saying.  My experience of these problems stems from the piano I 
bought just after I was married, and still have, the piano that was 
soon to lead me into the piano trade.  This is a 1905 Lipp upright, 
one of the finest uprights ever made.  When I tried to regulate it 
according to the few rules I had by then learned, I discovered that 
if I did the blow according to the book and the touch depth and 
set-off ditto, the hammers would burble and eventually settled on a 
touch-depth of nearly 11mm, which did feel deep.  One fine day 
another Lipp turned up with the case turned to dust by woodworm and I 
salvaged the keyboard, which had good ivory, unlike my old wreck. 
Not only that but the key ratio was quite different, for the same 
action. Problem solved.  One day I'll actually get round to fitting 
it!

>...Very well, then, let's get to the truth.
>
>I will follow up soon with some ideas on how we might handle this issue
>with a degree of organization, clarity, consistency and professionalism.
>Handled as such, we all might learn something.

I'd be very happy to cooperate, especially as I have a lot of 
work-in-progress on several aspects of the matter and need some 
stimulus to keep things moving forward.  As regards the programmed 
drawings and movies, the delay is due (apart from my innate tendency 
to let things drop) on the one hand to the sheer amount of 
programming work involved and on the other to the fact that the 
software tools to do the work are still evolving and not perfect, so 
there are frequent frustrations -- for example the tool that converts 
my SVG drawings to the vector PDF files that are needed to build the 
QuickTime movies won't deal with text, so  the text has to be drawn 
from scratch as SVG elements.

I will post some more basic stuff as time allows.

All the best,

JD



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