Leverage and Dip

[Bill Ballard]

At 8:06 PM -0700 10/2/02, David Love wrote:
>The action ratio not only refers to the relationship between change in
>weight at the hammer and the resultant change in weight at the key, it also
>refers to the relationship between key travel and hammer travel.  A quick
>way to calculate the action ratio is by measuring how far the hammer travels
>for a given amount of key travel.

Or measuring angular rotation of the key and hammer strike point. 
It's a little tricker but it allows you to take shorter sample of the 
stroke, say, cropping out escapement and after-touch. Just a note of 
spice up the discussion.

>The formula that would be useful to you is:
>
>(Blow Distance - Letoff) / (Key Dip - Aftertouch) = action ratio

That's a nice formula. may I clarify that a little? The dip and the 
blow both have one thing in common, a period of their arc when 
escapement is occurring (i mean by this the actual scraping out from 
under the knuckle). "(Blow Distance - Letoff)" seems to suggest the 
highest the hammer is lifted by the jack below it, which would 
include measuring through the break into aftertouch.

Would that mean that the motion of the hammer during the entire 
(however brief) period of escapement, was worth entering into the 
formula? I think not, The escapement is a period of decimated 
vertical motion, hovering on disappearance.

I'd much rather eliminate it, and I'm prepared to balance the 
equation so as to eliminate it. That means, stopping the sample of 
the dip right at the point where the key (at the front-most position 
in the lever train) first encounters the resistance of escapement. 
That way both arcs are cropped of areas of uncertainty. The equation 
is also balanced.

Unfortunately, RicB has asked us to use the entire dip and not a more 
abridged measurement of it, as mine is. So how do we figure in those 
missing amounts of travel? Well, they're in two parts. The 
aftertouch, you might as well dial in. The wild card in this is the 
portion of the key's stroke during which escapement is occurring. 
That depends on jack's leverage ratio, modulated by the rep's ratio.

I haven't gone out to the shop and measured anything yet, but I 
suspect that as the leverage shrinks (and the dip needs to increase 
for a constant blow) the portion of the key's arc during escapement 
is amplified. Inverse relationship. So Rick's problem is one more of, 
if his leverage is too high (and dip has to be reduced) will he still 
want the same size aftertouch? Or will he want to maintain the same 
proportions among the three components of the key's arc?

Only the Shadow Knows..........

Bill Ballard RPT
NH Chapter, P.T.G.

"All it takes is running your hands across the black granite at the 
Vietnam Memorial to understand what mistakes do
     ........... Sen. Lincoln Chaffee, Senate Foreign Relations Comm., 9/26/02
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