damper lever ht.

[Fred Sturm]

	For the sake of completeness, not just to annoy and be long-winded, I 
thought I'd offer a technique for determining the existing slope from key 
bottom at balance rail pin to damper underlever center, and thus how to 
determine the optimum height for the top of the keyend felt (for minimum 
friction between keyend and underlever).
1) Measure height of key bottom at balance rail pin from keybed. (call it 
<a>)
2) Measure height of damper underlever center from keybed (<b>).
3) Subtract <a> from <b> to obtain <c>, difference in height.
4) Measure distance from key bottom at balance rail to underlever 
centerpin. To to this, use a simple jig: a block of wood with at least one 
perpendicular face, that is at least as tall as <a>. If it is taller than 
<a>, either trim it or scribe a line at the height of <a>. Place this jig 
in the action cavity, lining up the perpendicular face with one of the 
lines created by the movement of the keyframe glides on the keybed (ie, 
with the use of the shift pedal). This line will correspond to a point 
midway between the balance rail pins of sharps and naturals. Measure from 
the scribed line to an underlever center (call this measurement <d>).
5) Calculate the slope of the line by dividing <c> by <d> (<c>/<d>). Call 
this <e>.
6) Measure the distance from the bottom of a key at the balance pin to a 
point on top of the keyend felt midway in the contact area between 
underlever and keyend felt. (call it <f>).
7) Multiply <e> times <f>. Call this <g>.
8) <g> plus <a> will be the optimum height of the keyend felt when it is in 
contact with the underlever, and when the underlever is half way through 
its travel. Call this <h>.
9) To get keyend felt height at rest, subtract 2/3 of the travel of the 
keyend from <h>. It's best to measure how much the keyend will travel, as 
this will vary somewhat with keydip and with key ratio.

	Writing this (and probably reading it) is more complicated than doing it. 
It might help to make a simple drawing, if the words aren't clear. Five 
minutes ought to be adequate to make the measurements and this calculation.
	Bottom line: This is really the only way to find out what is the optimum 
relationship of keyend felt to underlever for minimum friction. Whether and 
when the bottom of the underlever is horizontal may or may not have a 
relationship to this point. It's exactly the same procedure as determining 
the optimum relation between capstan placement and wippen heel thickness. 
And any other rubbing relationship between two levers. Minimum friction 
will be found when travel occurs equally above and below a line drawn 
between the two pivot points. I don't think any of us would worry about 
when the wippen's bottom was horizontal in calculating where to place 
capstans and how thick a heel to use, would we?

Regards,
Fred Sturm
University of New Mexico