Capstan Relocation

[Overs Pianos]

Richard and list,

Earlier I wrote;

>  Bill Ballard touched on the influence of the jack/roller relationship
>  to the line-of-centres in his recent post. His was an excellent
>  point. The location of the jack/roller contact for many actions, is
>  very poorly laid out.

Richard Brekne responded;

>Yet there are seemingly two somewhat opposing friction concerns here... the
>roller sliding on the repetition lever... vs the rollers contact 
>situation with
>the jack. I agree Bills point was a good one in as much as it addressed the
>unobtainability of this line of centers / knuckle consideration.

'Line of centers/knuckle optimisation' is obtainable. We have done it 
with our action (see my earlier post). The problem with conventional 
actions is that it is unobtainable when the wippen flange center to 
jack center distance is 99 mm and the roller slot to hammer center is 
only 17 mm. Why do manufacturers stick with this 99 mm figure? It 
seems that because Iserman used it and Steinway used it historically, 
most of the piano design world has gone into some kind of design 
paralysis, on the strength of a couple of manufacturers adopting a 
questionable layout.

The 'opposing' friction concerns to which Richard referred relate to 
two separate levers and their relationship to the roller, it is 
possible to design an action which deals with both matters separately 
in the one design.

Jack/roller relationship to the line-of-centers

During that part of the keystroke between rest and the contact of the 
jack heel/tender with the let off button, the wippen (with the 
repetition lever and the jack) acts as a single lever, ie. there is 
only contact of the wippen with the capstan, wippen flange center 
(fulcrum) and the roller. The arc relationship of the jack with the 
roller at this time is controlled by;

1) The jack slot to hammer center distance

2) The jack center to wippen flange center distance

3) The diameter (or more correctly - height) of the roller

4) The hammer boring distance (or more correctly - the arc of travel 
of the hammer shank during the execution of the key stroke)

Adjustment of any of the above parameters will change the jack/roller 
contact position with respect to the line of centers. All four of 
these parameter are standardised in the Overs action to minimise 
friction.

Repetition lever relationship to the line-of-centers

The repetition lever is, by and large, taken along for the ride 
during the execution of a key stroke up the point where the hammer is 
caught in check (while the repetition lever will have made contact 
with the drop screw - it is irrelevant to the parameters presently 
under discussion, since at the point of hammer check it is no longer 
in contact with the drop screw). At this point the repetition lever 
depression will be determined by the height of hammer in check. 
Therefore, before considering where to position the repetition lever 
center, the designer must first decided on a check height. I chose 12 
mm from the string as the height for the hammer check. I then set the 
repetition lever center height to intersect a line which passed from 
the hammer center and through the repetition lever/roller contact. 
This allows the repetition lever/roller relationship to be optimised 
at the moment the repetition lever pushes up (or holds up - during 
dynamic performance) the hammer as it rises out of check.

In an earlier post I wrote;

>. . the
>  jack/roller contact position is of equal importance [to that of the 
>capstan/wippen heel]

Richard replied;

>This is another point discussed a bit lately... and none of those 
>who seem active
>in action design parameters who have written about this lately have 
>seemed to see
>the importance of this..

But how can they fail to see? Just watch a standard roller on any 
Kawai, Renner, Yamaha or Steinway action model as it leaves the key 
rest position. The roller swings back as it rises - friction friction 
everywhere.

>I frankly do not see how this ends up being an important
>point . .  I would love to hear some explanation

Check out Terry Farrell's post. He's onto it.

Regards,

Ron Overs
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Website:  http://www.overspianos.com.au
Email:      ron@overspianos.com.au
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