Aftertouch Question

[Newton Hunt]

1/23" letoff is good for only on performance and only one. 
Regulating to that tight a tolerance exceeds the stability
of the wood and felts parts of the action.  If you do indeed
get ANY blockage when rise the hammer to the string slowly
the let off is too close.  1/16" is the design parameter and
the function parameter.  The drop screw and the letoff
button must be touched by their parts at the same instant,
that will define your drop.

The purpose of checking is to hold the hammer up so a
repetition can be done even after a hard blow.  If the
regulation is done as above and the pinning is correct at
hammer and rep lever centers (as Dan mentioned), the angle
of the Backchecks is about 68 degrees, the radius of the
tail curve is about 3" and the wood is not polished then
checking should occur.  If there is any blockage at all you
loose a lot of power and inertia and return speed that
checking will be compromised.

If you have a ridged enough hammer line representative on
the bench you will likely get closer in the box performance
than you will without one.  Bear in mind that the bench does
not have the same shape as the keybed and difference can
show up as regulation problems.

You after touch figure is a bit confusing.  After touch is
defined as the movement of the key from the time the jack
looses contact with the knuckle and the key comes to a
stop.  This movement provides a safety factor for the jack
to clear the knuckle entirely as the knuckle comes down for
the hammer to check.  If the knuckle just barely touches the
knuckle you will loose checking ability instantly.

The best measurement for after touch is about .045" +/-
.005" adjusted to the jack just finishes it's rub on the
knuckle.  Hammer height should be adjusted so after touch,
dip and hammer height provide the best compromises to
factory specifications.

You key dip of .450" is a bit deep.  Start with a dip of
.390" (10 mm) and change it -.010" or +.020".  Having dip
exceed .410" is ergonomically and anatomically
"challenging".  This means the pianist, especially those
with smaller hands, is being placed at muscular risk of
damage.  Deeper dip can produce a bit more power but the
price for that gain is too high except for strong
performance level pianists.

Whatever regulation you do on the bench must be carefully
rechecked in, at and on the piano because tolerances just
cannot be that accurately maintained.  I do all my grand
regulations at the piano and use the bench for replacing
parts and rough regulation.

Hope this is helpful.

		Newton