FWIW, I don't think it is a Zuckermann. Doesn't look like the old straight side model of jack (though it's been a while since I looked at one), and certainly isn't the "new" (1970s on) jack, which had/has no top screw. But the resolution of the film isn't enough to really see it.
David is right in saying that playing with the jack rail off doesn't tell you anything. It is like traveling hammers: we only worry about rest position to strike position. Same with jacks. If they can jump beyond where the jack rail stops them, parts of them can catch on something. It would be rare to play a harpsichord with the rail off and not have some jacks stay up.
But I assume you have a jack sticking problem, and troubleshooting comes down to three things. First, there is the key itself: remove the jacks, and see if it will return positively by itself. It might "float" back to rest position (on more refined instruments), but it should always return with the jacks out. So you address that if needed.
Second, there is the jack in the guides. There, you might want to lift the jack by itself (maybe remove some of the surrounding ones to have ready access) and feel it. Is there any resistance? upward or downward? The least bit of friction is significant. Then you seek it out. Could be too much of an angle, as David described. Could be the slot needs to be eased, and fore/aft is as much of a possibility as side to side. Easing should be done with extreme care, as you don't want to overdo it. The jack could be catching on the gap spacers that hold up the glide and maintain the space between the pinblock and the bellyrail. Sometimes there is a bulge or rough spot on the jack itself. Look carefully and figure it out.
Finally, there is the plectrum/string interface. Here, the best thing is to try to rest the plectrum on the (non-vibrating) string and see if it will stay there. IOW, play the note, damp the string, raise the key very slowly. See if it will stay. There are a few reasons it might. One is a burr of plastic at the end of the underside of the plectrum, from voicing. If your eyesight is good enough, you might be able to see that, or feel it with your finger, or see it with magnification. A second reason is too strong a tongue return spring. A third is too little distance between the plectrum and string when the jack is at rest: it can't hinge back far enough to let the plectrum reset. And the same symptom can be caused by a plectrum that is too long, extends too far under the string.
That covers the most common problems that would be described as "sticking," unless the symptom is not repeating reliably, in which case there are a couple more.
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Fred Sturm
University of New Mexico
fssturm@unm.edu http://fredsturm.net "When I smell a flower, I don't think about how it was cultivated. I like to listen to music the same way." -Federico Mompou
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Original Message:
Sent: 08-29-2013 21:58
From: David Doremus
Subject: sticking harpsichord jacks
The first step is to figure out exactly whats sticking. If you play with
the jack rail off they will often hang up and that doesnt tell me much.
Are they tight in the slide or in the lower guide? Are the springs too
strong? Is there too much overlap? There are a lot of possibilities and
you will need to look closely at the worst ones and try to diagnose
exactly where the problem is. Raise and lower them slowly, wiggle them
in their slots, see if they fall back freely under very slow release,
look how far the plectra stick out beyond the string when on. Try moving
the stop a little bit further off. See if the jacks are angled a little
too much in the on position, maybe in a move the slide positions
shifted? The dip might be too deep and/or jack rail too high. Those look
like old style jacks, and they did not ever repeat really well. You
might consider the conversion kit for the new ones which are more
responsive to begin with.
-- Dave
On 8/29/13 7:55 PM, Brian Doepke wrote:
> I have a client who has a Zuckerman (sp?) harpsichord, and as the video shows, some of the jacks on the right side line are sticking up and not resetting.
> While on the east coast, the instrument would perform well, but now in the midwest, some of the jacks hang up...but...the humidity at the time of the recording was 37%...not too extreme.
> Can anyone help with some suggestions to get rid of the sticking jacks?
>
> -------------------------------------------
> BD,RPT....FWA
> Fort Wayne IN
> 260-417-1298
> -------------------------------------------
>
>
>