[pianotech] Action Ratios Recap

[David Love]

Which is a good argument for using the weight method (SBR) as a solid check
for leverage and efficiency and is, in fact, what I do.  Moreover, it calls
into question the ratio of ratios that I mentioned earlier (PR/SBR) since
the PR is capable of producing such a wide variety of results.  

Bottom line seems to be that it's nice that there's a theory to act as a
guide.  In practice there's seems to be no way (at least that I've seen) to
avoid the tedium of testing.   

David Love
www.davidlovepianos.com


-----Original Message-----
From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of Nick Gravagne
Sent: Monday, January 18, 2010 10:44 AM
To: pianotech at ptg.org
Subject: Re: [pianotech] Action Ratios Recap

David Love wrote:

"In response to your post (below) ... I'd be interested to know which
different methods yielded which results."

1) The 5.9 AR yield was obtained by measuring the levers longitudinally;
i.e., no angles at all. For example, key levers are measured parallel, or
horizontal, to the key stick. Ditto on whip and hammer shank -- no angles,
everything longitudinal (more or less). This is a bit simplistic, but is
usually the way the concept of levers is taught in introductory college
courses.

2) RE the 5.7 --- measured on angles. The front key lever, per Pfeiffer, is
measured UNDER the key to the center of balance hole; the rear key lever is
taken from the balance to the top of the capstan (profile).
Ditto with the whip and shank --- all angles (see attachment). This method
is what is usually taught in action classes, with the at-times difference
that the front key lever is taken from the TOP of the front key, and then
angles down to the balance hole. 

NOTE: the short shank input lever at the knuckle is taken as an AVERAGE,
which is implied in the attached drawing and penciled in as "1/2 depressed".
In the case of the YC action an average shank value of 18.4 mm was used.
This is the method I mostly use, tho' I compare with the other two,
particularly the longitudinal method above.

3) RE the 4.6 --- measured exactly the same as the 5.7 with the exception
that the shank input lever is taken from the shank center pin to the point
of contact of the jack-top-to-knuckle at REST --- no half stroke and no
averaging of this lever. Some techs measure this way; to me it is
unrealistically low.

Now, I compared these three ARs with actual hammer rise to key dip and the
best "reading" I came up with was about 5.5 to 1 (hard to be precise). 

This is all a bit crazy as the difference between this "measured" 5.5 and
even the highest calculated AR of 5.9 is only 0.40; meaning that at the key
end the relative dip parameter relating to 0.40 "AR" is as small as 0.07 mm
dip (0.003"). Said another way, push hard enough on the key end to take up
the 0.003" dip, and the AR works out to 5.68, which compares favorably to
item #2 above.

RE the SBR stuff --- thanks. I will consider it.

Nick's post:
>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.  



Nick Gravagne, RPT
Piano Technicians Guild
Member Society Manufacturing Engineers
Voice Mail 928-476-4143