Key End Felt

[A440A@AOL.COM]

Avery writes:
>I have some firm green Renner felt that seems to be about the right
>thickness.  it
>seems to me that the only problem it would cause, even if it _is_ too
>thick, is to have to cut a little off the end of the damper wire.
>   Am I missing anything? Any thoughts, warnings, etc.?

Greetings,  
I don't think we can have too many warnings when it comes to changing damper 
geometry.  It is a subject that has fooled me in many way.  
    There is a particular geometrical relationship between the arcs of the 
key end and underlever.  The best relationship, from a friction standpoint, 
seems to be like the "ideal" relationship of the capstan to its pad. i.e.  if 
the range of motion is equalized around the common axis between centers, the 
relative motion between the parts is minimized.  Also, the more steeply 
angled the underlever, down toward the key end felt, the more friction.  
Steep underlevers also dig into the felt unless polished. 
     The underlever has its own "best height", determined by a number of 
things such as cavity room, damper tray travel, sostenuto height, spring 
pressure (if it has springs).  Combining these two "best" places is the art 
of compromise.  I try for making the common axis between centers and contact 
point occur at the beginning of the damper lift because I want the maximum 
speed of underlever for any given key speed to occur at the point of 
rest/contact.  I THINK it helps the damper seat faster to be returning to the 
string at this point.  
    Also, the softer the key end felt, the less obtrusive the feeling in the 
key at contact. (I may be obsessing, here.)
Regards, 
Ed Foote