Capstan Relocation

[Bill Ballard]

At 9:45 AM +1000 10/20/00, Overs Pianos wrote:
>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.

Agreed. My point however was not quite so concrete. It was just to 
say that with .52-3 KRs, his SWs still needed to be pretty good to 
avoid high FWs. Already the BWs are in the mild mid-30s. What we need 
to know now is what the FWs are that will tell if what is being 
balanced @ 35g BW is a serious (or slight mismatch) of SWs and SBRs, 
or whether it's a naturally mild-feeling action, ie. well hung.

(The acronyms have been introduced earlier in this thread. What, you 
weren't paying attention?)

>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)

Very nice graphic. You're still defining the problem in the linear. 
What we're selling to the pianist is not linear but but in the 
dimension of mass and weight (more specifically, inertial and 
gravitational forces). At what point do you move from adjusting 
length to adjusting weight?

>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.

Stephen Birkett is the one to best describe the complexities from 
with these deviation issues. In a spread-sheet model, in fact.

>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.

To my knowledge there's only one shank which will achieve this and 
that's the aeolean shank of the '20s, in which reducing the knuckle 
to the one quadrant of it actually used by the jack, cut the height 
of the standard knuckle by 1/2. You're right, none of the R&D dept's 
in our favorite piano factories  have been concerned enough with 
towing this line (axis) to find a better shaped knuckle, and we're 
all left playing actions with 150g+ escapements. Go figure.

>Website:  http://www.overspianos.com.au

Fabulous website, BTW. Would you care to talk about the Overs 
Modified Grand Action?

Bill Ballard RPT
NH Chapter

"I'll play it and tell you what it is later...."
     ...........Miles Davis