Ideal leading pattern: more questions

[Jon Page]

At 10:56 AM 04/01/2001 +1000, you wrote:
>><snip>
>If David were to reposition the capstans as Bill suggested, he may still 
>be able to get the hammer/key ratios he's looking for without changing to 
>17 mm shanks. Relative to the 17s, the 16.5 mm shanks will require the 
>capstan to be positioned a little closer to the balance pin (which will 
>slow down the wippen speed - therefore, check the jack tip/key ratio 
>also). I believe that attention to the hammer/key ratio should be the 
>first consideration with any action set up. The use of excessive amounts 
>of lead to get the required DW is a sure sign that there's something wrong 
>with the basic geometry (assuming that all of the usual suspects, centre 
>pin, bushing and balance pin friction have been checked).
>Ron O. Overs Pianos, Sydney Australia


Another interpretation of wippen speed is to think of the wippen as moving 
through a distance.
To achieve optimum regulation, the wippen must travel through a certain 
distance for the
jack to clear the knuckle. Too much distance and the jack buries into the 
stop felt, too little and
the hammers bobble on the jack.

As the capstan migrates towards the rear of the key the wippen moves 
through an increasingly
greater distance. This can be compounded by the capstan's interface with 
the wippen cushion. The
capstan moves along a small arc, as the distance from the balance rail 
increases, the arc
increases slightly as well. When interfaced with the wippen, the closer to 
the center pin (fulcrum)
that the lift is applied, the greater the resultant distance the front of 
the wippen travels thereby
moving the jack through a greater distance.  So by moving the capstan 
forwards, you are
decreasing the travel of the capstan and in turn applying that attenuated 
lift further from the wippen's
fulcrum thereby further diminishing the travel of the jack; also gaining a 
favorable mechanical
advantage which means the need for less force(weight) to be applied to 
operate the system.

There is a point on the key for the capstan/wippen interface where the key 
propels the wippen to
drive the jack so it just clears the knuckle for the given set of action 
specifications such as key
height/dip, hammer length/blow, shank geometry, string height and 
letoff.  Although I've found that
the jack travel is more dependant upon KR than knuckle execution in the 
final selection of new parts.

Many times we have to compensate on hammer blow or key dip to attain a 
desirable regulation.
Why not select the parameters with which you want the action to function.
A specified key height/dip, hammer length/blow, shank geometry, string 
height and letoff will require
the capstan to have the ideal location on the key for an interface with the 
wippen for the jack to be
suitably situated at the end of the key stroke.  That spot is the best KR 
for optimum regulation.
Form there you can assess touchweight.

Many times I find that major KR alteration is not necessary but that the 
angle of the capstan
needs to be addressed.  I think that perhaps the original setup design was 
valid but that its
execution failed in production. Try this:
Set the key with the hammer at half-blow.
Mark the 'magic line' intersection on the wippen cushion.
Draw a line on the wippen through that mark perpendicular to the cushion.
   (for a straight cushion: A small steel rule held parallel to the 
repetition support post
   and on the mark is sufficient).
Still with the setup at half-blow, extend the line onto the keystick.
Set the capstan at that angle and see what happens.
This has the center lines of the capstan and wippen interface moving 
through equal and opposite
   degrees from rest to letoff. (I'm really intrigued with Ron O's 
configuration)
It may not be the optimum position but it is a place to start. Fashion a 
'temporary capstan'
(jpg available) so you won't be drilling too many holes and can experiment 
with different locations.

I have reduced 'jack travel' by angling the capstan from 90 to 93 degrees 
without altering KR
(measured by a gram weight placed on the capstan).  I have also increased 
'jack travel' by
resetting the capstan from an exaggerated angle to one of similar slight 
inclinations retaining KR.

As for the 'magic line', I'm not 100% sure it really needs to be_at_the 
halfway point; afterall,
the sharps don't come anywhere near it. (or maybe that's their problem).

Regards,

Jon Page,   piano technician
Harwich Port, Cape Cod, Mass.
mailto:jonpage@mediaone.net