Touchweight Goodie

[Richard Brekne]

Hi folks

Here's a cute little fact perhaps not all you touchweight enthusiasts 
are aware of.  In anycase I just stumbled upon it yesterday evening 
dinking around with spreadsheets.

The key ratio can change without changing the top action ratio if you 
execute the change at the fulcrum instead of the capstan. An old trick 
for doing this is too glue a tiny peice of veneer to the underside of 
the key just behind the balance rail pin... or something simliar... but 
what effect does this actually have on BW ?

As it turns out it affects note 1 about twice as much as note 88.  With 
fairly standard values a 0.01 change in key ratio will change BW by 1.5 
gram roughly in the lowest bass, 1.1 grams in the middle of the piano, 
and 0.75 grams in the highest treble.

Heres a little spread sheet that shows what happens. You can change the 
input values for the top action ratio, the key ratio, the whippen 
weight, and the desired BW.  You can also change the range of SW's and 
the range of Specified FW's. 

The SW collum uses the ratio, whippen, and desired BW data to calculate 
the corresponding Stanwood FW values for reference.  The Spec FWs collum 
uses the ratio and whippen weight along with the SW range to calculate 
the resulting BW.

Just change for different combinations of SW, top action ratio, and key 
ratio and watch what happens to the BW for the sample values in the sheet.

http://www.pianostemmer.no/files/kr-to-bw-effect.xls


Sort of implies a neat way of  getting away with heavier hammer curves 
in the bass... a 0.01- 0.02 KR change in the bass isnt going to cause 
allllll that much differnce in needed key dip / blow / letoff 
conditions. But it will allow from 1.5 - 3 grams of decreased BW.... 
which can be turned around in terms of either heavier SW values (1-2 
curve up) or lower FW values (1-2 corresponding curves down).

Cute eh ?

Cheers
RicB