upright touchweight, mistakes and conclusions

[Keith Roberts]

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Mistake 1; Assuming action geometry would solve an upright weight =
problem.

Mistake 2; Assuming leading would solve an upright weight problem.

Mistake 3; Assuming a little stronger jack spring wouldn't hurt.
Mistake 4; Assuming...=20
Mistake 5; Assuming....

This is theory, I'm assuming I'm right.

I thought action geometry could solve a touchweight problem on an =
upright. First clue; I have heard it said (must be an old wives tale), =
"you can hang a heavy hammer because the weight of the hammer doesn't =
matter in an upright".  True.  A mistake would be to not lighten the =
hammer as much as possible. A too heavy of a hammer will crush the butt =
leather and pressure the flange bushing and not have a clean rebound. =
However, the ability to accelerate a heavy hammer is there. The key here =
is knowing that the wippen in an upright is a 2nd class lever on the =
lift and a 3rd class lever on return. In a grand, the opposite is true. =
So an upright being a more efficient lift mechanism, mass is less =
important. The upright action geometry is designed for proper =
distance/movement of the wippen and touchweight becomes a factor of the =
spring tensions, a variable, instead of gravity which is not a variable. =
You might want to change the geometry if the blow distance was set at 1 =
and 7/8" with a key dip of 3/8" and a jack that hits the letoff  rail. =
Damper lift also needs to be considered. Then the wippen travel might =
need to be lessened.

Back to touchweight. The jack spring is a significant factor in the =
touchweight. I had a 57 gram DW and a 37gr UW. Both the tall Pianotech =
spring and the Schaff spring were too tall. I could have determined this =
by measuring the height of the jack flange. The one on this Knabe is =
short in comparison to the replacement options. So I replaced the jack =
spring with a spinet jack spring from Pianotech and the DW became 47 =
grams and the UW was 20 grams. I would have thought this was wrong if =
Michael Gamble hadn't posted the target weights from the S&S manual. =
Thank you Michael. Obviously the jack spring affects the UW far more =
than the DW. It functions somewhat as a wippen return spring. It will =
aid in lifting more weight at the front of the key. The effort of the =
jack spring is a 2nd class lever. The effort of the hammer weight is a =
3rd class lever and so the hammer spring will have more effect on the DW =
than the UW. The springs control the DW and the UW. =20

Upward pressure is needed at the capstan. This would be to maintain =
capstan/wippen contact during both the up and down movement of the =
wippen. This upward pressure is limited by the weight of the wippen and =
the low UW and the need of the wippen to drop quickly without the weight =
of the hammer. Leading needs to balance the key against the wippen =
regardless of hammer weight. The wippen needs to fall on it's own weight =
to allow the jack to reset and have lost motion. Leading therefore =
should be to balance the keys as an individual component.  Any change in =
feel will come from the change in hammer weight on acceleration or =
messing with spring weights.

Please comment, discuss, call me stupid or ignorant but substantiate and =
show the way.

Keith Roberts
kpiano


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