[CAUT] CAF

[Richard Brekne]

Hi Fred.

Still not sure we are on the same page here.  I agree that excessive 
distance between the rest cushion and the hammer shank will cause 
repetition problems...  But my understanding of CAF is when the jack 
simply gets locked in the window, between the knuckle and jack stop 
cushion resulting in the hammer laying below the hammer line. Usually 
this doesn't just easily snap back on itself but requires a bit of 
jiggling the key to get reset.  I never have had THAT condition and 
found that the distance between rest cushions and shanks was the 
problem. I've seen that condition with very minimal rest cushion to 
shank distance as well. Most of the posts accent the friction in the 
relevant centers along with implications that friction has for whippen 
spring strength. Thats where I find the CAF condition fault as well. 
That said.. I suppose very close distance between rest cushion and shank 
might ease border line conditions.

I have Eric as a <<neighbor>> and we get together often enough... I'll 
make sure and have a nice chat with him about this next time we get 
together. Always enjoyable to chit chat with him regardless of the reason.

I see no reason to doubt you Fred, nor did I find anything do disagree 
with in Davids post.  I <<tentatively>> agreed with Jeff because full 
blown CAF seems to be related to the whippen, and not the cushion/shank 
distance.  That said... excessive distance between these latter most 
certainly is a detriment to optimal action response.... and I wouldn't 
agree that we don't <<need>> the rest cushion.

I'm still unsure of just how often the shank actually hits the rest 
cushions... never really thought about it. I have run into the loose 
rest rail thing as well, we all have but that thing will make noise just 
in sympathetic vibration as well... so I am unsure as to what that says 
about actual percentage of time the rail or cushions get in contact with 
the shank. Its and interesting tidbit, a bit to the side of this 
issue... but you've got my curiosity up :)

Cheers Fred.
RicB



    I'm not surprised you can't reproduce it on a model. It seems to
    take a rare set of circumstances for it to happen. When I first ran
    into it, a pianist left a note after rehearsal, saying notes X, Y
    and Z were having repetition problems sometimes. I checked them,
    found nothing amiss, did the usual odd bits of things to optimize
    repetition  (regulation, spring tension). Dress rehearsal, and the
    pianist called:  "I'm still having repetition problems with those
    notes, and it is in very obvious places" (can easily be heard by the
    audience). So I went into the hall and had her show me. Yep, no
    question there were problems. After watching and listening to what
    she did, I was able to  make it happen. I'm not sure I could do it
    again at this point, but I could do it consistently at the time. It
    had to do with precise timing of a second blow on the key, as well
    as the precise way the first blow was executed (pretty hard and
    staccato). What seemed the easiest solution was tacking a bit of
    felt onto those cushions. Presto! Problem solved. (All shanks were a
    good cm or more above the cushions).    Since then I have heard a
    number of fellow techs describe the same  thing. Within the past 3 -
    5 years, at a NYC Steinway Academy session,  Eric Schandall
    mentioned that you needed to be sure the shanks were close to the
    cushions, as otherwise a certain kind of action lock up  could
    happen. Sounded like exactly the same thing.  So, be my guest,
    believe it or don't believe it. You may or may not  ever run into
    the problem. But it is not just my own personal  imagination. It is
    a hallucination shared by others. And anyway, it's  a good idea to
    have that distance close for other reasons, partly as  described in
    my last post and by David Love.
    Regards,
    Fred Sturm
    University of New Mexico
    fssturm at unm.edu