Low Inertia

[Fenton Murray]

David S.
Please clarify Efficiency Ratio. Weight Ratio divided by Distance Ratio? Lights are coming on and someone might actually be home. I'll be glad to study links you might provide if that waves you some verbiage here.
Fenton
  ----- Original Message ----- 
  From: erwinspiano at aol.com 
  To: pianotech at ptg.org 
  Sent: Monday, October 06, 2008 8:07 PM
  Subject: Re: Low Inertia



   Hi David
    
     No..Just me.  I missed the string height business. D's are an engaging study in ...the huh? factor. Love em fix em.. Listen to great music on em. Get paid to fix em.  Doesn't get any better.
    Dale


  Hi Dale, 
   
  Your e-mail came through with alot of question marks!!! I think your computer is confused..... 
   
  As I said the cp heights were all almost 1/4" low.... and the string height was a little high.. we raised the stack up as high as we could without the drop screws being in danger of hitting the wrest plank. This was a 1947 D. 
   
  Chris Solliday and I worked on a 1946 D which had the cleats in backwards The wip centers were way way low... no one could ever regulate that piano until we put the cp heights back to spec by replacing and reorienting the cleats.... and getting the cp heights back to spec... 
   
  I think it was so soon after the war effort and maybe they were out of practice after making so many Gliders....! 
   
  David 
   
  ? David 
  ? This?is a fascinating development! I'm curious. How high was the hammer flange center pin from the keybed before it you moved it up??The blow was the same ? 
  ? By the way what vintage of D? Do we ever know enough...rhetorical question 
  ? Thanks 
  ?? Dale 
  ? 
   
  Dear all,? 
  ? 
  Before these related threads scatter into oblivion I want to restate what I've already mentioned in the Journal past: it is my observation that distance ratio divided by weight ratio yields something I call the efficiency ratio which is a ratio of ratios....? 
  ? 
  As an example I was recently working in John Foys shop to help install a Precision Touch Design in a Steinway D. We found that with a 5.5 ratio the distance ratio was 5.0. The efficiency ratio was .9 and the action required a .430" dip with a 1.75" blow.... We checked the action center elevations and the whole stack was low by almost 1/4". Rechecking the ratios the weight ratio was 5.3 and the distance ratio up to 5.7 which was kind of astonishing. The efficiency ratio was now 1.1 and the action regulated with .400 dip...? 
  ? 
  This is just one example and I'm collecting much more data to formally publish but I can say at this stage that it is my conclusion that the efficiency ratio should be above 1.0 for good results...? 
  ? 
  To me distance ratio comes under the heading of geometry and is related to arcs and their angular interaction whereas the strike weight ratio is a result of vertical gravitational vectors.? 
  ? 
  I like what Fenton said.... it's about Hammer Weight, Action Ratio, Geometry and Friction....? 
  ? 
  Onward and upward....? 
  ? 
  David Stanwood? 


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