[pianotech] Action Ratios

[David Love]

Sure, please do.  

 

I know how to measure the AR with weighting (SBR) but in this case it's not
practical to use that method nor does that method really give you any kind
of regulation information.  I have to relocate or reconfigure capstan,
wippen rail and wippen support (not to mention find a shank that works with
it all) and so the distance method work better here.  An after the fact
measure of SBR will be done to see how the two relate and to be sure that I
can target the weights specs I want.  But first priority is regulation
specs.   I typically have a target distance ratio of somewhere around 5.5
(5.2 - 5.9 is probably the standard range) but as you can see this formula
doesn't really yield that on the right side of the equation.   

 

Del gave me some good information on a similar action he worked on awhile
back and I think I have the solution to this particular problem but I'm more
curious about the equation below because it doesn't seem to work or the
letoff and aftertouch numbers are figured from somewhere that I'm not
getting.  I suppose if the aftertouch number were quite a bit larger than I
have figured (though I then wonder exactly what aftertouch means in this
case) one could make the formula work.  Otherwise, the denominator is too
large.   

 

David Love

www.davidlovepianos.com

 

From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of Jim Busby
Sent: Tuesday, January 05, 2010 12:49 PM
To: pianotech at ptg.org
Subject: Re: [pianotech] Action Ratios

 

David,

 

Can I forward this to Rick? He's going to NAMM so it might take a week.

 

Also, have you tried David Stanwood's method for measuring AR with weighing?
Just wondering why this is rarely discussed/used. Anyone else use this? 

 

Jim Busby

 

From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of David Love
Sent: Tuesday, January 05, 2010 1:20 PM
To: pianotech at ptg.org
Subject: [pianotech] Action Ratios

 

I'm having to revisit using distance formulas to correct a serious action
problem and in the process have been reminded (thanks Jon) of the
Baldassin/Robinson formula of:

 

(keyout/key in) x (wippen out/wippen in) x (shank out/shank in) = (blow
distance - letoff)/(key dip-aftertouch)

 

The left side of the equation is common to all of us who use that to
calculate the action ratio.   But the right side is less common and doesn't
really make sense in terms the relationship between action ratios and
regulation.  While the left side of the equation describes the relationship
between key travel and hammer travel unimpeded by let off (for example in an
action with a 5.5 ratio, 10 mm of key travel will produce 55 mm of hammer
travel).  But the right side of the equation doesn't bear much resemblance
to that outcome for that type of ratio unless my let off and after touch
dimension are quite misguided (I figure 1.5 mm for let off and 1 mm for
aftertouch-in reality I use about .030" which is more like .75 mm).   I'm
curious if anyone has actually used this equality to set up or make a
correction on an action.  If you use the right side as a guide it will tend
to set the target action ratio far too low, in my view.  

 

David Love

www.davidlovepianos.com

 

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