[CAUT] CAF

[Andrew Anderson]

Ric,
My example involved the hammer tail engaged against the backcheck  
below the hammer line, yes the jack was stuck between the knuckle and  
the stop felt but that was secondary to being caught in check while  
bouncing too low.  This happened on repetition too fast for the action  
in the state it was and cushion 1/2" below the shanks.  I have another  
D where the piano proff complains that the action is slow and yes the  
cushions are low.  On very rapid play, especially involving  
repetition, the hammers are busy exploring their bounce when they  
should be reset and ready.  The local Steinway tech. thinks the piano  
is "just fine."

Andrew Anderson


On Aug 17, 2009, at 6:28 AM, Richard Brekne wrote:

> 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
>
>
>
>
>