>> There is too much friction at the string/pin interface to allow the >> string to slither up and down the pin under normal conditions. > >I'll accept this, grudgingly, until such time as I can prove otherwise. Like I said, does the string slither back and forth on the V bar? >I can readily see where the string would find it difficult to move upward >against both the friction and the vector force, but could imagine it >displacing downward, against less friction and in the direction of vector >force. Which is why the string follows the bridge top back down the pin in dry cycles. There is, as David love said, a chance that pin damage already incurred by this wear to interfere with both the upward and downward motion of the string. >Nevertheless, it should be possible to estimate the additional load of a >pitch rise of, say 440 to 445. Yes, it is. This comes up on the list every few months. An arbitrarily chosen scaling file shows, at 435, 36168lbs total tension, and 682lbs total down bearing (calculated from bearing angles and tensions). The same piano at 440 shows 37004lbs total tension, and 697lbs total down bearing. >I should be able to do it, but can't, yet. It just seems that whatever >rise could be attributed to board height increase would be pure load, not >the pinching of the string by an expanding bridge top against angled pins. Even with negative front bearing? Have you ever measured zero or negative overall bearing in a piano that has gone sharp with a humidity increase? I have, and that doesn't fit your scenario. Besides, it's not the rise that's the issue. It's the change in bridge surface relative to the pin. Fifteen pounds of extra bearing divided up among 230 or so strings isn't going to put a heck of a lot more pressure on the bridge cap under each individual string compared to the 20+ pounds the bridge top takes at each pin pushing the string up the pin. > Likewise, you or someone else in possession of a brain might be able to > calculate that portion of the pitch increase that could be attributed to > a .030" increase in bridge height. Yes I can, at least to reasonably illustrative rather than precisely predict. It requires specifying the starting pitch, speaking length, wire diameter(s), back scale length, overall bearing angle, and overall string length from tuning pin to hitch. I think that's everything except friction. >By the way, is it possible to relate the 4% and 12%MC that you referred >to earlier to relative humidity? Do you have a copy of the excel spreadsheet I offered a while back? >I don't know...it just seems like you're saying something different. Can >you explain? You want me to explain something you think seems to be something I don't see? Uh... no, I don't think I can. >Why DO you care about the string contact with the front edge of the bridge? Because when it doesn't, it eventually leads to tone production problems and false beats when the pin gets loose in the bridge. It's a practical consideration rather than a theoretical one. >>I disagree. Poor front termination, with the accompanying tonal problems >>and false beats, becomes most problematical when the overall front >>bearing angle (that between the bridge top and speaking length) is very >>shallow. A strong positive front bearing angle DOES put the horizontal >>string termination on the notch edge and none of this stuff even comes >>up. It's only when that angle becomes shallow enough that the crushed >>notch edge no longer contacts the string. We've gone over the basic >>points a number of times reducing them to ever finer isolated details. In >>the piano, they all exist and interact at once, each in relation to other(s). > >Here's perhaps where we are still farther apart, and the fact that we've >gone over basic points in ever finer detail should be viewed as purely >positive achievement, in my opinion, not a source of exasperation. Did I say I was exasperated? The interrelationship is my point, and all these details have to tie back into the whole to make sense. > I absolutely agree that strong positive front bearing would obviate > these issues, though it could also have more of a tendency to compress > the notch edge and migrate the wood contact forward of the pin, but > that's a problem to live with. Yes it would, but not nearly to the degree that the seasonal movement of the bridge surface and string up and down the pin do. >The fact is, I almost NEVER come across anything BUT shallow to negative >front bearing. Likewise, chiefly because the soundboard crown that was supposed to be holding that bridge up to maintain that front (and overall) bearing is also minimal to negative. >I use a Lowell gauge, but as a determinant for front bearing, I measure >the smallest possible segment behind the pin to compare with the sounding >string segment. As it relates to termination, that's the only relevant part. I disagree. >I also slide the gauge to the rear pin to observe the amount of >curvature along that segment. It can range from .009" to .050", with the >.030" range not being unusual. What's that in degrees? If you're using the rise per inch from the graduations on the Lowell gage, that's 0.003" per 10' of angle, isn't it? So you're telling me you measure anything from 0.5° to over 2.5° of curve over bridge tops? Then again, holding a straight piece of wire in the groove in a bridge top, tangent to the curve of the groove at the notch edge, it will likely show more angle than that. I wouldn't consider this to be a healthy bridge, but as you say, it's what we see the most of in the field. OK, now how could front bearing that never was over 2° produce a 2.5° or greater indentation? >First of all, in all of our recent back and forth, your statement to that >effect at the top of the page is the first time you've ever stated this, >so it seems unfair to make it sound as though I'm simply being thick-headed. I'm not going looking for it, but I have said that the pin was the primary termination, rather than the notch. >Second, I'm sorry to parse your usage, as you sometimes do mine, but you >say no "significant sliding motion", which, of course, makes me wonder, >just how much "insignificant" sliding motion IS taking place? I have no way to measure it precisely. When you do, please let me know. With inadequate pin angle and/or inadequate offset angle, I know the string does indeed slither up and down the pin. It sounds like a dobro on drugs, and is pretty hard to miss. And if I said NO motion, I would certainly be challenged to prove it. When I see and hear a piano with provably perfect string terminations, I'll have something by which to judge. Meanwhile, I'm attempting to get across what I consider to be reasonable, accurate and factual information pending something that makes more sense to me. >Lastly, the analogy with the V bar is interesting but flawed. The offset >angle of the string at the bridge pin is considerably less. How much angle difference constitutes "considerably"? At what point does "considerably" become significant? And I have certainly seen deflections across V bars that are similar to and even less than the horizontal offset across some bridges I've also seen. I think the analogy is quite valid and not that casually dismissed as flawed. > The direction of string excitation is perpendicular to the V bar but > parallel to the bridge pin. (If the hammer impact was proximate to a > vertical termination, wouldn't you expect some string displacement? Strings vibrate in all directions, not just in the vertical direction of initial excitation. You hear the tonal problems and false beats long after the string has migrated from it's purely vertical excursion path. >If you believe that the tightness of the pin in the bridge is the prime >determinant of the presence or absence of false beats, why do you find >negative front bearing unacceptable? Loose pins with low front bearing. Because pins don't stay tight forever, and I'd rather see the redundant support of both the notch edge and the pin at the same point with positive front bearing so there's enough friction between the string and the bridge top to keep even a loose pin from flag poling and making a beat. Wherever I can get one, I'd rather have a definite than a maybe. I've tuned a lot of pianos that sounded pretty good and acceptably clean in the humid summer months, but became un-tunable with false beats and other termination nasties in dry winter months. Pianos with tight pins and good crown and bearing don't tend to do this. I said the string doesn't "have" to be touching the bridge at the pin, and it doesn't to produce good tone, but it's more likely to produce good tone for a longer period if it does. >Thanks again - Hope you feel better Thanks, but I'm allergic to the planet, or at least the part of it I'm currently in, so it comes and goes at random. Just another day. Ron N
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