[pianotech] A.B.Chase Grand Piano

[Ron Nossaman]

On 11/26/2010 10:46 AM, Terry Farrell wrote:
> Interesting knuckle arrangement on your piano Clark. I certainly don't
> consider myself an action expert, so take anything I suggest with a big
> grain of salt (never stopped me from speculating though). Maybe someone
> like David Stanwood or Ron Overs might be able to offer some critical
> thinking on this setup.

Well, I'm not anywhere near being an expert either, but a couple of 
things strike me about this design. As Jack said, it's quiet. There is a 
lot of padding between the wooden knuckle and the wippen, and a lot of 
surface contact area making for a low psi loading between the knuckle 
and the contacting leather. I haven't tried to set it up and analyze it, 
but the large knuckle curve strikes me as potentially minimizing the 
slide between knuckle and "wip" through the stroke. I'll put that one on 
the shelf pending a better evaluation by someone with better tools than 
I have. One thing that is real though, is that the large knuckle curve 
(not a radius, probably involute), produces a considerably more 
progressive action ratio as the key is depressed, than does a modern 
action. I don't see how this would be possible without the intermediary 
piece between jack and knuckle, as the necessary jack contact point 
wouldn't move to allow it. I presume this is the primary reason for the 
design, but that's just a presumption from what I see.


> A few better pictures of the arrangement would help also. Is the
> "knuckle lever" on a spring?

I don't see one. Why would it need it?


>It appears it has an action center at the
> rear end of it. Obviously it functions as the hammer shank knuckle. But
> what is the advantage of having the knuckle independent of the shank?

Perhaps the above reasons I've offered.


> There appears to be an adjustment screw going through the rear portion
> of the repetition lever, just forward of the repetition lever height
> adjustment screw - it looks like it has a piece of red felt on the top
> side of the repetition lever and the screw goes through it - picture is
> fuzzy - what's that all about?

It appears to be an up stop, as is found on a lot of wippens.

Ron N