upright touchweight, mistakes and conclusions

[Erwinspiano@aol.com]

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Hi Keith 
  I read your post & any one reading this  will have a better understanding 
of the dynamic relationship of action parts in  an upright. Nice job. Yes even 
your mentor learned a few  things.
  I have often weigh  upright hammers in the  big old uprights we restore & I 
find the original hammer weight is always  light as are the grand from the 
time period
    . On the Ludwig upright currently  in process & used the AA Wurzen felt 
with the Maple moldings & I found  that even tapering the whole set in my 
tablesaw jig I was still a fair bit  heavier but close enough. I juiced only the 
bass lightly. The rest of the set  got nothing except the usual filing  that you 
& I are accustomed to.I  find uprights do not need or benefit from  a heavy 
hammer & that extra  weight really tend to kill the sound especiall in the top 
3  octaves.
 Thank you grasshopper
   Regards
   Dale

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... 
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.  
 
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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