On Nov 30, 2010, at 9:58 PM, David Love wrote: > But even though > flange friction is essentially a moving target (just like tuning and > voicing) I still believe it's worth addressing along with the > necessary > compensations that those choices entail. Hi David, Good post. I agree with what you have to say, essentially. I would concur that a reasonable level of consistency in friction is important and desirable. I'd like to expand on the question of the impact of centerpin friction on touch. (Let me say that from here on, I am not addressing David specifically, but the list in general). Let's start with the hammer, 4 gm vs. 0 gm + a bit. 4 gm measured at one inch translates to less than one gram at the hammer's center of gravity, which is somewhere around five inches out from the center (simple ever, so 4 divided by 5). So pinning a flange that has 0 or so gm friction to increase it to 4 gm would have an impact on the hammer's throw somewhere in the vicinity of impeding its movement by one gram resistance. Intuitively, that doesn't seem like much, doesn't seem like it would have a significant tonal impact by itself: hammer of X mass at Y-Z range of velocity being braked by one gram's resistance, maybe someone on the list has the math and engineering background to do a reasonable modeling. But let's go back to the key and touch. The friction resistance at the hammer gets multiplied back by 5-ish because of the key/hammer ratio (nominally 5:1 in the opposite direction), so 4 grams friction measured at one inch from the centerpin translates to 4 grams at the key, at least nominally. Or so my calculating brain would say, and maybe someone has measured to confirm: does pinning a flange from 0 to 4 grams increase DW by 4 grams or so? This time of year, I have no time to do other than tuning and the necessary, and I've forgotten what I came up with years ago when I fooled with that. Let's assume it is correct. Hence, the initial impact on touch is simply addition of resistance to the finger, maybe 4 grams. As we depress, we hit a couple obstacles, the first being the damper. An aside, but an important one: amongst all the talk of evening hammer weights and strike weights and friction, I don't recall any discussion of damper lift resistance as a component of touch. Does anybody actually measure this? Seems like something that ought to be included, since pianists do play without the pedal and with "half pedal" (usually just lifted enough to bleed but not be entirely open). But let's do what "everyone does" and ignore it, press down the pedal and proceed to the next obstacle. That would be the drop screw pressing down on the key through the rep lever and the spring. Maybe the jack tail touches simultaneously, or maybe just a little later (I think that either is acceptable as long as they are quite close, and the jack tail shouldn't touch first). Let's take the jack rubbing against the knuckle out of the picture for the moment (raise all the hammers in the air), and isolate the springs pressing down on the back of the key. The pressure is dependent on the strength of the spring, and increases as the key is depressed and the spring is compressed. The lower the drop is set, and the more aftertouch you have, the more pressure builds up at the bottom of the keystroke. I think this concept is one that can't be emphasized enough when it comes to concert and high end work - OK, and other work as well. Rep spring strength is dependent on friction of the hammer center and the rep center, so if those have been jacked up pretty high, the spring resistance will be way high. WIth those hammers in the air, press down on five keys lightly with five fingers to feel the resistance, as a way of isolating that aspect of touch. (Pressing on five at once is a good way to feel more precisely, as it is when estimating DW by feel). I think (judging by pianos I run across) that there are a lot of techs out there worried about getting checking at pianississimo, and pinning tight, checkering tails, increasing drop to accomplish this, and it is not a good thing IMO. Let the hammer not check at pianissimo, no harm done. Far more harm done to the touch by increase of spring tension and amount by which the spring is compressed (drop adjustment), again IMO. My point in raising this issue is to counter the notion that more hammer and rep center friction is a good thing because it makes regulation go better. Maybe it does make it easier to make specs (nice even hammer rise from check, easy to get the jack under the knuckle), but going overboard has what I believe to be a negative impact. Back to the touch scenario, putting the hammer back down, the feel of the action from the moment of impact of the rep lever with the drop screw through aftertouch is arguably the very most important element. German instructors (as I remember from classes by Bechstein, Seiler, and Schimmel reps, as well as at the Sauter factory) emphasize the additional DW required to take the action through letoff. They say it should be in the 10 gram or less vicinity if memory serves. Much of that is friction of the jack against the knuckle. If there is too much friction in flanges and too much spring tension, that will also come into play here. I've gone on long enough for now. Regards, Fred Sturm fssturm at unm.edu "Travel is fatal to prejudice, bigotry, and narrow-mindedness." Twain
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