Let-off button felt compression vs let-off timing

[Dan & Martha Reed]

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From: "Dan & Martha Reed" <pianoman@airmail.net>
To: carpthos@televiso.com
Subject: Let-off
Date: Fri, Feb 25, 2000, 10:52 PM


Tom:

    I really like your awareness of this problem. I have wondered about
this, but never thought to single out the reasons why.
     I would be willing to bet the bundle on compression of the knuckle, as
the #1 reason that let-off moves away from the wire, faster than compression
of the let-off button felt tries to move escapment  closer. The weight of
the hammer is constantly compressing the knuckle, as it sits on the jack.
Try this test. Place a piece of thin felt, like key bushing cloth)  or even
something as thin as a business card between the knuckles and the jack tops.
Now compare the "new" height, in relation to the hammer height adjacent to
these. Because the hammer is way out on the end of the lever, a little
movement of the knuckle (compression) is magnified greatly. (I would guess
about a 10 to 1 relation here.)
   The #2 reason would be that the hammer felt has worn away. Before
dismissing this 2nd. reason, compare a new hammer with a worn one on these
old pianos.
    Any other felt compression would not change the let-off position.
Compression of the back rail cloth, balance rail punching, capstan contact
felt, hammer rest felt or even movement of the key bed, won't change let-off
timing. These other changes will reduce how far the whippen (i.e. jack)
travels, and these changes can be so limiting that the jack won't complete
its let-off function.
     The blow distance is usually 2" plus in these actions, with let-off
happening 1/4 plus from the wire. The jack is making it to the let-off
button, but there is usually not enough remaining jack travel to get the
desired after-touch. Of course, the real problem here is: no control of
pianissimo:and poor "average" response.)
    The real clairifying test, to check out what these other compressed
felts do, is to crank the capstan up or down, and measure if this changes
where let-off occures.
     I am teaching a class at the National convention this summer very much
relating to let-off timing.
It is called "Performance Regulation / Voicing in Everyday Service." If you
can't make it, and are interested more in this subject, please keep in
touch.
Dan Reed 

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