Action Ratio and Dip and Blow and Etc.

[Ron Overs]

Hi Terry and all,

>Yes, there is room in the rep lever window to move rearward up to 
>even three millimeters. Take a look at the following photo:
>
>
>
>You can see that the jack long axis and the knuckle core axis are 
>pretty close to parallel with one another.

Yes, it looks quite good. That jack tail angle also looks better than 
most contemporary efforts (which dig holes in the lett-off button 
felt). But you probably could take the knuckle slot out to 17 mm 
without upsetting the alignment, since the jack is kicked back a 
little towards the hammer centre when at rest.

>As you can see, I increased the wippen heel height quite a bit to 
>get the heel/capstan interface on the magic line at half blow - that 
>modification has decreased friction a fair bit.

Indeed, this is always a good move. But just look at the above image, 
and watch what will be happening as you move the knuckle further out 
on the hammer shank towards the hammer without changing any other 
parameters. Especially note what will be happening to the contact 
point between the knuckle and the jack contact face. It will be 
moving towards the wippen/hammer-shank line of centers. The same 
tendency will occur if you reduce the diameter of the knuckle. Also, 
as you move the knuckle out, the wippen/knuckle-contact-distance from 
the wippen centre will be reducing in length, while the distance from 
the knuckle to the hammer centre will be increasing. Therefore, the 
overall hammer/key ratio will be reducing just as it does when you 
move the capstan towards the balance pin. Both adjustments therefore 
will reduce the hammer/key ratio.

>
>Take a look at the lead in the keys in the photo below:
>
>
>
>That's where my concern about lead stems from. All front weights are 
>0.96666 of Stanwood's maximum front weights.

Yes, I suspect that this action has a hammer ratio which is too high. 
The number of leads is always a tell-tale sign of a higher than 
desirable ratio (assuming of course that the keyboard weigh-off was 
done just after checking the friction of all the key bushes and 
centers)

>Are you thinking that the slight loss of efficiency at not having 
>the jack perpendicular to the shank at rest will be more than offset 
>by the action ratio becoming more efficient by moving the knuckle 
>out?

The relationship of the contact between the knuckle/jack contact with 
respect to the line of centres will be the most significant factor.
>
>I've never moved a knuckle before.

While it doesn't take too long to plug the knuckle slot and re-cut 
it, I prefer to check an action at tear down these days and make a 
decision on what to order, so that I don't have to do major custom 
work at the time of re-assembly. You can get the overall ratio you 
are looking for by moving the capstan line alone, but if you've got 
an action with a 15.5 mm slot distance from the hammer center, and 
you're using contemporary weight hammers with say 10.5 gr for the 
lowest bass, you'll need to move the capstan much further towards the 
balance pin to achieve a desirable ratio than you would if you 
ordered shanks with a 17 mm slot distance.

Ron O.
-- 
OVERS PIANOS - SYDNEY
    Grand Piano Manufacturers
_______________________

Web http://overspianos.com.au
mailto:ron at overspianos.com.au
_______________________
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