---------------------- multipart/alternative attachment Ron - Here it is I thought I was doing better, and it turns out you were just too under-the-weather to do a full number on me. I'll continue to take my chances. From here I'll pretty much go back out and look at some more pianos. Thanks. You've given me a good deal to think about, even if you think I should already have know it. At 05:19 PM 4/3/2004 -0600, you wrote: >>I accept that a vibrating string contacting the notch before the pin will >>cause tonal deficiencies that would not be present if the pin were to be >>contacted before the notch, however, what I'm talking about in this >>thread is not a defined notch whose contact with the string occurs >>closely after the bridge pin, but rather a tangent relationship between >>string and a rounded or mis-planed bridge surface, the contact points of >>which could (when string is not seated) take place 1/4" or more to the >>rear of the pin. In such a case, it would seem that the horizontal >>bridge surface can only be supporting the position of the string on the >>pin,(as a later quote of Ron's states) but making no direct contribution >>to the string energy termination. If that support is far enough from the >>pin, it would seem to allow some slight amount of vertical sliding >>movement at the pin, even with a 10 degree angle. This movement would >>cause accelerated wear and flattening which could, in turn, cause tonal >>distortion. > >That's one of the traditional explanations for false beats, that the notch >edge is too deep, and (with the bridge pin) forms two different speaking >lengths for the string. Problem is, that it doesn't work that way. 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. 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. >Boy, I shouldn't try to do this stuff when I'm sick and my brain isn't >working.. It's bad enough when I'm well and my brain isn't working. Let's >try that again. > >Root height went from 0.842" to 0.868", or +0.026" height change. >Cap height went from 0.253" to 0.257", or +0.004" height change. >Pin height above the cap went from 0.127" to 0.119", or -0.008 height change. > > >>Also, the other value that would establish an accurate picture would be >>the height differential of the board. > >That's another set of problems. Since the bulk of the bridge damage comes >from the expanding bridge pushing the string up the pin against high >friction and down vector force from the pin angle and offset, that was >what I was interested in exploring. Nevertheless, it should be possible to estimate the additional load of a pitch rise of, say 440 to 445. 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. 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. By the way, is it possible to relate the 4% and 12%MC that you referred to earlier to relative humidity? >>>If the string isn't contacting the notch edge, it's for a reason that >>>tapping neither string, nor pin will cure. >> >>While I basically agree with you, I'm finding it difficult to reconcile >>with your response to Wim's "More Wood, less pin..." questions: > >I don't see any inconsistency. Explain please. In response to me you wrote: >I do care about the string contact with the front of the bridge, but I do >not agree that tapping the pin will achieve that end. That's the whole >point of all this. If the string isn't contacting the notch edge, it's for >a reason that tapping neither string, nor pin will cure. In response to Wim, you said: >Wimblees: >>There has been a lot of discussion about tapping the pin to create better >>tone, less distortion, etc. But what are we doing? Is the better >>termination caused because by tapping we are driving the pin deeper into >>the wood at the bottom of the hole, thus creating a more stable pin, >Ron N: >Partly, but I think mostly dragging the string down with the pin to the >notch edge. and >WimB >>So what is the real reason for tapping? More wood, or less pin? >RonN >Or seating the string by proxy? I don't know...it just seems like you're saying something different. Can you explain? Why DO you care about the string contact with the front edge of the bridge? >>>Front bearing is the angle between the string segment on the bridge top >>>and the speaking length segment. >> >>My contention is that, since the string segment on the bridge displays >>considerable curvature, it is misleading to think of angles or to assume >>that the imaginary straight line between front and rear bridge pin is >>meaningful in defining the angle actually formed by the two string >>segments as they converge at the front pin. > >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. The fact that all of this interacts in the piano should not preclude trying to view it in such detail, if doing so refines our, or my understanding. With regard to what you state above, 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. The fact is, I almost NEVER come across anything BUT shallow to negative front bearing. 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 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. >>>As I point out. I've also pointed out that this local negative front >>>bearing from tapping a string down isn't to be considered to be overall >>>front bearing. It results from doing something that isn't indicated from >>>the cause of the symptoms - seating strings. >> >>This is where I either lose you or disagree. When you say "this local >>negative front bearing from tapping a string down...". I'm not sure how >>to interpret this. Yes, if you don't seat the strings to the bridge, you >>won't read it as negative, but you have the potential problems discussed >>above, relating to excess string movement at the pin. If you do seat it, >>you eliminate, temporarily the sliding movement on the pin, but introduce >>an unstable condition which will eventually return the string to its >>neutral, elevated position. But, at the beginning and end of this >>comment, you seem to again assert that the condition is caused by string >>seating. I see no reason to support such an assertion. > >As I've been trying to explain to you, there isn't a significant sliding >motion on the pin. Is there a sliding motion of the string on the V bar? 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. 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? Lastly, the analogy with the V bar is interesting but flawed. The offset angle of the string at the bridge pin is considerably less. 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? DS >>Then I understand your use of "climbing the pin" to refer to a string >>moving upward on a pin in spite of positive bearing angle. >RN >And/or in spite of a positive down vector force from pin slant and offset. >To me, climbing the pin means the string has moved some place where it >doesn't belong and needs to be put back in it's natural place, when in >fact, the low, zero, or negative front bearing angle and crushed notch >edge mean that it is already in it's natural place (if not it's desired >place) and tapping it down to the bridge puts it in an unnatural place >under the circumstances. > >And as I also have said, I don't consider negative front bearing to be >acceptable in a conventional piano. And yet: (from Thu, 01 Apr 2004 15:48:01) DS >> I'm asking "why does the string need to contact the front edge of the >> bridge?" >RN >It doesn't. I suspect you have tuned pianos in which this was the case. I >know I have. As long as the bridge pin is solid in the top of the cap, >there won't be a false beat to lead someone to tap the string - or pin. 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? Thanks again - Hope you feel better David Skolnik ---------------------- multipart/alternative attachment An HTML attachment was scrubbed... URL: https://www.moypiano.com/ptg/caut.php/attachments/a5/ee/4a/ba/attachment.htm ---------------------- multipart/alternative attachment--
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