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

[Jon Page]

In the Robinson/Baldassin class in Providence "Truth & Consequences"
they stated that not only was the capstan to intersect a line between the
b/r and wippen center pin at half-dip (my term) but also the surface of the
knuckle is on a line between the wippen c/p and the hammer flange c/p.

An involved formula accompanied the drawing on the handout. Which had
nothing to do with the diameter of the knuckle but rather its proximity to
the hammer c/p, action spread, key ratio and hammer height.

The height (diameter) of the knuckle will affect the situation of all parts
concerned. So the appropriate diameter/radius should be selected to best
accomplish optimal parameters.  A larger knuckle will have the hammer
closer to the string at this halfway point and will consequently affect
aftertouch.

In the Renner USA Parts Kit, two different diameter knuckles are supplied.

Jon Page

At 11:46 AM 10/6/98 -0500, you wrote:
>
>
>----------
>> From: Dave Swartz <dms2000@PIONEERPLANET.INFI.NET>
>> To: pianotech@ptg.org
>> Subject: Re: S & S 'A' parts, geometry -- shanks and flanges
>> Date: Monday, October 05, 1998 11:54 PM
>> 
>>.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?
>> 
>> Dave Swartz, RPT
>> dms2000@majesticpiano.com
> 
>Dave, 
>	If you mean a varation in the diameter of the knuckle between .357 and
>.395 I would notify the maker and insist on closer tolerences.  To put it
>in prospective a varation of .038 is close to a .040 medium thick
>cardboard br punching, or almost 1mm.    
>Also where the knuckle is at rest is where it puts the  hammer hammer at
>the correct striking distance.  Which begs the question, "What difference
>in striking distance is caused by a varation of .038? If the ratio is one
>to seven, then the furtherest two hammers will be from each other is 7mm. 
> 
>	Now 10mm is .3937, I am wondering what size knuckles were installed. 
>	I think of where the knuckle is placed on the shank is how far the jack
>has to move up and down to make the hammer move X distance. I am not sure
>how the size of the knuckle affects this distance, since every thing is
>measured from the center line of everything, and distance traveled (which
>is always circular with levers) is determined by distance from center of
>rotation. (a radius) 
>
>Richard Moody 	
>
>