[CAUT] fulcrum of a key

[Fred Sturm]

On Oct 2, 2009, at 3:28 PM, Don Mannino wrote:

> So, perhaps the central issue of your topic is: Is it desirable for  
> the
> rotational axis of the key to move fore and aft during play?  Now  
> that's
> a question.
>
	I guess that if we do the split punching thing, we reduce the  
movement (toward the player, "backward") of the fulcrum, and make it  
more precisely in one spot, especially if we cut it in half at the  
middle of the hole. When we do that, we put the fulcrum right at the  
center of the pin/hole. So that would seem like it might cause a  
fairly large difference in performance. Of course, when we do this, we  
are doing it for a different reason, shifting the ratio as a whole to  
reduce DW, so it is hard to tease out what part of the change we might  
be feeling.

> As for the firmness of the balance punching, well, yes, harder is  
> better
> for the touch.  I think we'd all like the precision of metal washers
> under there, but between the noise and the damage to the pianist's
> tendons, I think we prefer to live with the vagueness of nice firm
> bushing cloth.

Hmm, if it were really firm, as in metal washer (supposing we could  
make it noise free), wouldn't the fulcrum be pretty precisely set at  
the lip of the washer toward the front of the key, meaning that we  
would have "more or less precision" and no movement of the axis. With  
spongy cloth, when the key is first depressed, we could say the axis  
is at about the middle of the balance pin, while the felt is first  
being compressed. But then it rolls forward along the felt and perhaps  
ends up near the front of the felt. Firmer felt would be closer to the  
metal washer. Which is better? That's one question.
	Another question, and one I was trying to get at, was having to do  
with the ability to analyze an action geometrically. When I have tried  
to measure all the lever arms (key, wipp, and shank) and do the fairly  
simple multiplication and division, I have come up with a ratio that  
is a good bit different from what I get with measurement of dip versus  
hammer rise, or of variation by weight (adding a known weight to the  
hammer and measuring how much heavier BW is at the front of the key).  
So I'm thinking that some point in back of the balance hole should  
probably be used when calculating the key ratio for this purpose.  
Maybe it should be as far as the edge of the punching.

Regards,
Fred Sturm
University of New Mexico
fssturm at unm.edu