On Aug 15, 2009, at 8:52 AM, Jeff Tanner wrote: > Fred, > Yes, practice at regulating spring tension does help. But my > experience is that when balancier and hammershank pinning is too > loose, the spring tension regulation has to be so light that it > isn't reliable. The spring has to regulated so weak that the > slightest changes in humidity have a great effect on function. To > regulate the spring tension so that it doesn't throw the hammer past > the drop point against the string, creating the bobbling hammers at > mp playing, you wind up with a spring not strong enough for the > wippen to reset properly on a firm blow. More firm pinning prevents > "bounce", especially in the jack, but also in the hammer. The > stronger spring tension allowed by firmer pinning "lasts longer". > > So, yes, I agree with Chris on this. Yes, there are many causes, > but every occurrence I've ever run into has to do with pinning, > spring tension, or a combination of the two being out of tolerance > on either side. But I've always been able to remedy CAF with other > means than changing the rest cushion height. There are a couple things here. First, there is the question of what we are calling "CAF." I am referring to a particular lock up of the action (of one note of the action), where the hammer ends up well below the hammerline, and it doesn't reset immediately. It sometimes resets within a second, but that is too slow. Sometimes it resets if you just lightly touch the key. Sometimes it stays locked until the key is depressed a couple times. It is, as I said before, a fairly rare symptom, which occurs with particular sorts of playing, but can be very, very aggravating to someone who plays that way, or plays particular passages. I, just like you, have had pianos with hammers high off cushions with zero complaints. And then, if somebody else plays the piano, the problem occurs. And, I repeat, and with emphasis, the only cure is a closer cushion. Talking about this precise problem, not about "action failure" in general. Now there are plenty of other causes for action failure, especially having to do with the jack getting back under the knuckle. It can be sluggishness of the jack center, rubbing of the jack in the window, a few things. There is one symptom that is more connected to rep pinning. When you check an action at rest by tripping jack tenders very lightly, during the final regulation of rep lever height (relative to jack top): ideally you should see the hammer fall very slightly (maybe 0.5 mm), and when you release the jack, it returns and the hammer rises again that 0.5 mm. Sometimes the hammer drops more and the jack doesn't return, and you screw the adjustment screw, and keep screwing it, and, well, it just won't be made to work. In that case, commonly too loose centers is the cause, maybe both rep lever and hammerflange. Usually you find zero friction. And usually repinning solves the problem. (The one case where I have found that it doesn't is with the old Baldwin wippens, which have the odd coil in the spring that goes directly between rep lever and jack. It seems that the action resets under actual playing conditions, but in checking by tripping jack tenders, it worries the heck out of me. They don't reset nearly reliably enough. Pinning tight and maxing spring strength doesn't do the job. Maybe I am missing something. Fortunately I only have one L like that, and it is in a classroom. I guess I have also had that experience with Schwander wipps. Mostly I work with butterfly springs, and I think I see why everyone uses them). So, yes, some degree of firmness of rep lever pinning is needed for the action to reset in many cases. For myself, I would say 2-4 grams. Others are talking 7-9 grams. I think that is excessive. And I'm not sure the heavier pinning makes the spring strength adjustment last longer. I'd say the opposite, that it is more likely to need to be adjusted sooner, that you will end up with bobbling and re-striking hammers sooner. If the spring is adjusted against less friction, its adjustment is closer to what it would be at zero friction, so it won't really change a whole lot as things loosen up with play (or dry). Regards, Fred Sturm University of New Mexico fssturm at unm.edu -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://ptg.org/pipermail/caut.php/attachments/20090815/3da7b369/attachment.htm>
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