S & S 'A' parts, geometry -- shanks and flanges

[Dave Swartz]

At 10:38 PM 10/5/98 -0400, you wrote:
>Ok, Richard, good reasoning but let's take it a little further.
>
>By increasing the size of the knuckle (your numbers are good) the
>capstan has to be turned down thereby taking it off the optimum line
>between key balance point and wippen center pin.  This will increase
>force required to depress the key.

Richard & Newton:  Great posts...here's my 2 cents:

That optimum line theoretically defines the capstan moving through the line
as the key is halfway depressed.  In some cases (once hammers are bored
properly, strike weights are smoothed and the key ratio is optimum), turning
the capstan down to accomidate (sp?) the larger knuckle will improve the
leverage point from balance rail pin to whip centerpin, but can increase
friction ...weight accentuates friction.

Interestingly enough, should you use one of the 3 Renner parts for
(Steinway) replacement, you will notice grave inconsistencies of knuckle
sizes within the same set of hammer shanks.  Not so much in the 15.5 mm
(knuckle core to centerpin) and not so much in the Hamburg style
(17mm)...but measure the modified 16.3 mm set...I've taken readings from
.357 to .395 in the same set!!!  Does it not also effect the relationship
from whippen centerpin to hammer flange centerpin?...Where's that knuckle
supposed to be at rest?

>You did not take the knuckle relocation far enough.  You know that we
>have a simple lever and that changing the lift point toward the pivot
>point will decrease the leverage and greatly increase touch weight
>because a minor change of knuckle location is considerable amplified by
>the leverage of the key.

This is one of many parts problematic of obtaining a consistent strike ratio
throughout the action (in my opinion). 


Dave Swartz, RPT
dms2000@majesticpiano.com