[CAUT] Repetition ( was Steinway center pin height)

[Richard Brekne]

Hi Ed

Comments interspersed below:


       Any action will fail to repeat if the second note is struck
    before the
    key resets under the knuckle.  There is a minimun distance the key
    must be
    allowed to rise before the reset.  If the key is struck before this
    minimum
    distance is achieved, the jack will either skip or will not touch
    the knuckle, at
    all.  On a normal action, this is just a one time failure and as
    soon as the
    key is allowed up, the note will once again repeat.

Yes... and on any well regulated grand action I know of... this distance 
is well less then the full return of the key to its rest position.

           On an action in which the hammershank cushion is too far
    below the
    hammer's resting position, the skip, (cited above) allows the
    hammershank to fall
    so far that the capstan is holding the whippen too high for the jack to
    reset.  In other words, the knuckle is below the lowest jack height
    possible.  
    Hence, a note that doesn't play until the hammershank is bounce up
    into the jack's
    range.  
           ( I hope that makes sense...) 

Sure it makes sense.... except that the skip shouldn't happen if the 
hammer is allowed to fall that far.  Even in the condition where the 
hammer isnt checked because of very soft play.  Even if the jack does 
skip and the capstan holds the jack top higher then the knuckle 
position... you should be able to just regulate the capstan low enough 
to alleviate that condition. This should worst case result in non 
standard key dip.
 

        <<  The rep lever is supposed to lift the hammer via the knuckle
        up to a position where the jack can slip under as soon as
        (nearly immediatly after) the key is released.  >>


           I must respectfully disagree.  The purpose of the rep lever
    is to
    increase the speed of the key return.  We measure the spring
    strength by watching
    the hammer rise, but in rapid repetition, that event doesn't occur. 
    Under
    fast repetition,  the hammer shank doesn't rise between blows, but
    rather, stays
    at checking distance while the key and whippen, (under the influence
    of the
    spring), return to their "reset" position.  One can ascertain this for
    themselves by playing middle C so that the hammer is held in check,
    and then slowly
    depressing B3 so that the hammer is at drop.  Simultaneously,
    release both keys
    and observe that the C return far, far more rapidly than the B.

While I'll agree that the rise doesn't occur during usual play (at least 
not with full key release and moderate spring and key mass levels), I do 
not agree that this is synonymous with stating the purpose of the rep 
lever is to increase the speed of key return.   The purpose of the rep 
lever is to allow the action to return to firing position before the 
released key is fully returned.  If the jack isnt under the knuckle well 
before that...then something is clearly wrong.  Every action I regulate 
allows for fast rapid repetition without the key anywhere near full 
return. This can easily be demonstrated by artifically limiting the 
height of key return to say 3/4 full return. You should still be able to 
play quick repeats.

          One can also see, on an action model, that when the key is
    released
    while the hammer is held in check, the hammer doesn't rise, but
    rather, drops to
    its at rest position. Under high speed conditions, there is no time
    for the
    hammer to rise between notes.

This happens because when we test rep spring we hold the key down and 
barely release pressure so as to see how much rise we can induce... its 
a test.  But in real play the same forces are are work and these forces 
do the same thing relative to the parts as under the test... the only 
difference is that some of that force is allowed to push downwards on 
the key and the other half of the whippen... the end result should be 
pretty much the same.

         This is why there is no difference in repetition speed between
    a spring
    that slams the hammer off the jack when released and a spring that
    simple
    lifts the hammer as fast as possible without being felt in the key.

I must disagree here as well.  First and formost because it is nearly 
impossible to not feel the rep lever pushing against the key if you have 
any real pushing strength in the spring.  And because the difference 
between that extreme and even reasonable firm lift using the standard 
test, barely releasing the key out of check, does indeed result in a 
difference in repetition speed.


     Unfortunately, many regulators destroy the sensitivity of
    escapement by pursuing the former course in the mistaken belief that
    it improves repetition.   Checking height has far more effect on
    repetition speed than anything else.

I'll agree that there is a limit to how fast the action can be made to 
play... and how strong the rep lever should be felt through the key... 
but this is a bit more complicated then just so... involving relative 
tightness of jack and rep lever centers... hammer flange centers, and 
for that matter whippen flange centers and key bushing friction.  
Checking height has likewise limits....   All this said... it is easy 
enough to regulate an action so that it plays faster then then ability 
of any human to play.

    Regards,
    Ed Foote RPT

I cant say I've ever run into this condition perse'.  I've seen things 
somewhat similar... but these are always regulation issues.  I still 
don't see how relative positions of the center pins comes into all 
this.... tho I am sure someone out there can explain this to me.

Cheers
RicB
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