Key Ratio

[John Hartman]

Dear Mark,

I have been studying action mechanics in the last several years. I too
started by studying Pheiffer. What I have come to realize is that
Pheiffer's books were intended to describe his research on various
advanced action design and function topics. They are not primers on
basic action mechanics. I have not found any books that directly
describes how the piano action works but have managed to piece together
the basics from physics, mechanics and engineering texts. Even if
Pheiffer is not a good place start, if he has inspired you to brush up
on your algebra, trig and geometry he has set you on a good path.

This may be more than you want to hear but I would like to make a few
suggestions. Fist limit you studies to either the grand or upright
action. Though they work very similarly  this will simplify you job.
Second, start with mechanical static's, the study of bodies in
equilibrium. Work on the lever lengths and forces. Pheiffer's  "The
Piano Key And Whippen" pgs. 45-52 as well as "the Piano Hammer"
pgs.108-111 are the true beginning of the path(forget about the rest of
the book for now). Thirdly, limit your early studies to the action's
motion up until the jack contacts the let off button. Fourthly, build an
adjustable action model that allows you to change the key ratio, action
center positions as well as change to various action parts. This way you
can test your ideas (check out the PTJ article by Ted Sambel about
making a adjustable modle).

I don't want to give too much away because I think you will have a lot
of fun making your own discoveries but I have outlined a few key issues
below.

Moments of force about a point. Useful in finding the position of leads
in the key.

Transmission of motion by direct contact. Essential to finding the true
lever arm lengths of the shank front arm and wip. back arm. (the common
normals of the contacting profiles bisect the line of centers).

The arcs of motion(fig, 29 pg.47 Pheiffer the key and whippen) are
directly related to the forces.

Each of the three levers have a ratio. The product of all three ratios
will be the transmission ratio of the action. This equation can be
transformed to find any of seven unknowns.

John Hartman RPT


Mark Bolsius wrote:
> 
> G'day List
> Jon, for an out of touch Aussie tech whose PianoTek catalogue is 5 years out
> of date, could you enlighten me as to the details - who makes it? and what's
> the cost of this wondrous jig
> maybe a catalogue number if you have it handy, I'm veeeeery intrigued.
> 
> Also my newfound friends, I'm starting to research action design and
> geometry in both grands and uprights and would appreciate any leads
> regarding reading material. I'm currently wading through Walter Pfieffer's
> two books The Piano Key and Whippen and The Piano Hammer, and my Journals go
> back only a bit over 4 years.
> 
> Any suggestions?
> 
> I'm also planning on being at your national convention this year in Kansas
> City, but the more I can discover and understand before I come, the deeper
> my learning can be. Looking forward to meeting some of you there!
> 
> Thanx in advance
> Mark Bolsius - Canberra Australia
> markbolsius@optusnet.com.au
> ----------
> From: Jon Page <jpage@capecod.net>
> To: pianotech@ptg.org
> Subject: Key Ratio
> Date: Wed, 27 Jan 1999 1:10 PM
> 
> Here's something to break the monotony:
> 
> Why are some piano's key ratios so erratic
> and other a closer tolerance?
> 
> Is the hole that much off note to note to create
> a .02 to .05 difference?
> 
> I have not taken linear measurements for this, (can one?)
> only a weight on the capstan with the key on the
> scale platen. Next time I'll scrutinize length parameters.
> 
> I have to put in a plug for the Touchweight Design Table.
> (Pianotek)
> If speed and accuracy conforms to your procedures, then
> this tool fits that bill. I thought my own jigs were doing just fine.
> 
> Having ordered one at the Providence Convention I thought
> I would be apprised of their availability but fortunately one arrived
> last month. What a difference!
> A side by side comparison proved the benefits of their system.
> 
> I highly recommend this tool for techs interested in further
> development of their action diagnostics.
> 
> Regards,
> 
> Jon Page
> Harwich Port, Cape Cod, Mass. (jpage@capecod.net)
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~