[CAUT] S & S D rest cushions

[Fred Sturm]

On Aug 14, 2009, at 2:04 PM, Jeff Tanner wrote:

> "Catastrophic Action Failure" happens because checking is too low,  
> hammer flange, jack or rep lever pinning too sluggish or rep springs  
> doing absolutely nothing at all.  Not because of rest cushions.  We  
> shouldn't even need rest cushions or rails.  I've had the same  
> issues with hammer shanks having to be so high above the rest  
> cushions to get aftertouch with reasonable keydip and never one  
> issue of catastrophic action failure unless one of the above was the  
> cause.


	Maybe you haven't experienced it. I have (with all those other  
variables within good parameters). It happens with specific types of  
playing, and is rather rare, but it can be a "catastrophic" problem  
when it occurs in a concert. It has to do with specific timing of a  
hard, staccato blow and what happens to the key following the blow.  
Sometimes it is a matter of a fairly rapid repeat, sometimes just a  
matter of the key not let up all the way before the hammer has  
completely rebounded (the key keeping the wipp in a somewhat up  
position). In any case, the result is a jack jammed between knuckle  
and rep window cushion, which the rep spring can't overcome, I guess  
because of geometry. I have had the complaint, have asked for a demo,  
and have been able to reproduce the symptom. The only cure was getting  
the cushion closer to the shank, and it was definitely a cure. This  
after checking all those other parameters.
	Ask Eric Schandall, he's had precisely the same experience and  
strongly recommends that cushions be very close to shanks. I expect  
Kent Webb would tell you the same.
	"We shouldn't need rest cushions or rails" is a rather naive  
statement. There are, actually, reasons manufacturers include them,  
this being one of them.
Regards,
Fred Sturm
University of New Mexico
fssturm at unm.edu





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