Capstan Relocation

[Overs Pianos]

Richard, Bill and list,

Terry Farrell wrote:

>  > KR is between 0.52 and 0.53.  WWs range from 17.5 to 18.5 in the factory
>  > configuration.
>

Richard Brekne responded:

>Hmm... those are certainly low enough for a light touch.

The key ratio alone will tell us practically nothing about the 
performance of an action. The hammer/key front ratio is the factor 
which will give an indication of the way in which an action is likely 
to perform. It is not the back of the key we interested in lifting 
when we depress a key - it is the hammer! The back of the key (more 
particularly the capstan) is merely the means to an end by which the 
hammer is lifted.

The key ratio alone will tell us nothing unless we use it, as we 
must, to calculate the overall ratio of the action, ie. the 
hammer/key ratio.

There are three leverage elements in the grand piano action;

1) the key
2) the wippen
3) the hammer

The ratios of each of these levers must be multiplied together to 
give us the hammer/key ratio.

The following link will take you to a drawing on my website, showing 
the measurement points we use to determine the hammer/key ratio.

http://www.overspianos.com.au/anrt.jpeg

Hammer/key ratio = (B/A)*(D/C)*(E/F)

It is possible for two different actions with identical hammer 
weights, hammer/key ratios, wippen weights and centre friction to 
have differing overall action friction. Much of this has to do with 
the condition (ie. smoothness) of the capstan and jack surfaces (eg. 
an unpolished capstan which has machining marks on it's surface can 
increase friction by 1-2 grams), and the nominal offset of the 
capstan/heel contact and jack/roller contact from their respective 
line-of-centres.

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. While it is important to have the capstan/heel 
contact pass through the line-of-centres at half key dip, the 
jack/roller contact position is of equal importance. I find it 
incredible that almost all piano action designers over the past 
century have failed to grasp this.

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