Minimum LO, WAS: Hammer assist spring ?

[Bill Ballard]

At 9:45 AM -0700 6/7/03, Delwin D Fandrich wrote:
>This is the part that intrigues me. The ability to set very close 
>letoff and the ability to control the action at pianissimo levels.

At 7:46 AM -0700 6/8/03, Delwin D Fandrich wrote:
>So, when I hear some say some grand action design can be regulated 
>with let-off right up to within 1 mm of the string line I at least 
>want to give the thing some thought. And one of those thought is, "I 
>wonder how this thing would work with a nice graphite-filled ABS or 
>Nylon jack?"

Are you perhaps thinking of the final turnstile the hammer has to go 
through to make it to the string, the friction barrier of escapement? 
At the initial turnstile (DW, or in a non-friction world, BW), 
nothing happens until you put the correct number of coins in the 
slot. At escapement, with the hammer's momentum, at least you get a 
consolation prize for being a dollar short: a "Viennese escapement". 
As in the Prell-mechanik, the rep lifts the hammer until the jack 
tender hits the LO button,  and because the driving force at the key 
is less than the escapement friction, everything stops dead in its 
tracks. Except for the  hammershank, which if the LO is close enough, 
has enough momentum to go the remaining distance. On its way back 
down from the string, it is checked not by the rep spring pressure in 
drop, rather by sitting itself back down on the jack which has not 
moved from its pre-LO position, because escapement never occurred. 
The most obvious part of the consolation prize is the hiccup we all 
know and love, when the hammer bounces (albeit, slowly) off the jack 
and grazes the string again.

I've always believed that one of the least easy of factors 
determining the threshold sound (ie, minimal LO) to control is 
escapement friction. It's partly a function of jack alignment, 
jack/rep spring strength, knuckle shape and leather friction, 
hammershank ratio and SW. It's nice to inventory these factors, but I 
have often been in the situation of unable to alter escapement 
friction nearly as much as I'd like.

Escapement friction is a turnstile. You can reduce the hiccuping by 
fattening the LO. But the size of this friction determines the 
quietist sound one can get out of a piano. So Del, would the 
lubricity of the jack top make a big difference here?

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

"Can you check out this middle C?. It "whangs' - (or twangs?)
     Thanks so much, Ginger"
     ...........Service Request
+++++++++++++++++++++