[CAUT] moving capstans question

[A440A at aol.com]

Keith writes:


> Do I care if the the action ratio was 5.52 or 5.59? No. I'm sure I could 
> make an arguement that shows that the BW is not exactly halfway between the UW 
> and the DW. Do I care? The instantaneous action ratio can change through the 
> movement of the action. It can have one action ratio at the start and another 
> at the finish as the parts move. Do we use the max ratio or the average or a 
> section of movement that we consider to be representative? The reason there 
> is a difference in these ratios is the criteria set upon the way it is 
> measured and not because the action puts out three different amounts of work.
> 
Greetings, 
    It may be of interest that check the EAR with 3 succesive 2mm key 
depressions, to see if the ratio stays the same. It will not!   As the capstan 
approaches the axis 'tween centers (the"magic line"),   the ratio begins to steepen, 
as it pass the line, it begins to lessen. If the capstan contact point 
arrives at the line at let-off, you will notice that the ratio increases up to that 
point.   In effect, the action starts in low gear and is shifted to high by 
the end of the keystroke. 
      Given that the highest ratio is found at the line, as is the minimum 
friction,(which is dependant on relative speed of the capstan to the heel ), an 
action   that has the capstan on the line at the half-way point is an action 
that begins to have its ratio decreased as the hammer is approaching maximum 
velocity. This is counter-productive, in that after the inertia has been 
overcome, and the hammer speed is increasing along with the ratio, a decrease in the 
ratio halfway through the travel will cost power, unless the finger powering 
the action can somehow increase its speed through the last half of the key 
travel.   
    If the capstan reaches the line at let-off, the point   of maximum 
friction has been placed at the very beginning of travel,where the speed of the 
relative motion is at its minimum and the ratio is at its most advantageous.   
Through the stroke, the ratio is steadily increasing as the friction is either 
decreasing or staying the same, due to increased speed of relative motion, 
ultimately reaching the point of zero friction and maximum ratio at escapment.   I 
have found this set-up to give a measurable increase in power and control.   I 
think the idea of setting the "magic line" may be the factory production 
attempt to minimize the variability in the production line, itself.   
     This is why I prefer the capstan/heel contact point reach the line at 
let-off, not before; it creates a "magic point" right where the pianist looks 
for maximum control.   
Regards,  
Ed Foote RPT



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