>Hi Phil > >First off, lets keep our shirts on here and not assume either is getting >impatient with each other ok. Your note sounds like you are making some >assumptions about my attidude, and I assure you they are as friendly and >lighthearted in spirit as can be. Sorry if I formed the wrong impression. Phrases like 'we are witness to numbers being used to attempt to "prove" that...' don't sound friendly and lighthearted to me. Call me hypersensitive. >Secondly... let me address two points. First the immediate one below. I >asked you whether you are taking this position about side bearing >increasing because no one has shown it to be true, therefor its an >assumption, and one I dont buy into. Why ?? because the side deflection of >the string simply does not change with dimensional changes in the bridge >wood due to climate changes. This sounds strange..? Perhaps because one >thinks that as the bridge suface grows they are pushing the strings higher >on the pins and thus more sideways bearings ? But if you stop to think >about things for a second one must see that it is the position of the >bridge pin holes themselves that define the sideways deflection. And they >do not move sideways because of dimensional changes in the wood. As the >bridge expands the angled bridge pin holes will tend to straighten out a >bit, lessening if anything the actual angle of the bridge pins. Not to >mention that the pins themselves are being pushed upwards as it is >claimed. So in actuality, you have bridge pin holes that do not change >their relative position to each other... so no way of increasing side >bearing there,... and a stress on the pins themselves that go in the >direction of lessinging their angle... which if anything would decrease >side bearing. OK. This is the sort of specific comment that I was looking for. I see your point. I had been thinking that as the cap moved up relative to the pin that the string would move out because of the bridge pin angle, increasing the side bearing. Perhaps it won't, or perhaps it will actually decrease a bit as you say. Anyway, what I tried to indicate in the previous post was that increasing side angle wasn't part of the assumption that I made when calculating the bearing stress. There is a static friction at the bridge pin based on the force on the pin due to whatever side bearing is there, which I assumed to be 8 degrees. Whatever is happening to the side bearing due to the movement of the bridge cap relative to the pin isn't going to change this angle by much (also note that 8 degrees is not high - some pianos will be higher - increasing the static friction force). There is also downbearing. If the bridge cap is going to move up relative to the pin, and the string is going to go with it, then these forces have to be overcome. By my calculation in a previous post the stress induced in the cap was 4080 PSI. This is considerably higher than the 1500 PSI allowable. Do you think that this is not happening? If so, why? Which of the assumptions used in making that calculation do you think is (are) wrong? I'm not trying to 'prove' that this is the only mechanism by which the bridge cap could be indented. I don't know what's happening due to string vibration. Maybe that's contributing. The only way I know to establish that is some sort of experiment. But the numbers seem to indicate that the string's resistance (or more properly - the string's interaction with the bridge pin) to movement of the cap could crush a maple cap. So, this certainly would seem to be an appropriate area of investigation in any experiments to try to understand cap damage. Also, you bring up another good point which I don't think I've seen mentioned. As the bridge moves relative to the pin, the pin hole is probably not going to want to stay parallel to the pin. So, the bridge is probably trying to tweak the pin, as you say. This may put considerable stress on the edge of the hole at the cap surface, which would tend to enlarge the hole, which would tend to make the pin loose, which would tend to exacerbate pin flagpoling, which some think is the source of false beats. The more you look at it, the more this pin termination seems to be a bad idea. ... >So... as to the brass experiment. It simply isolates the possibilty >for crushed bridge surface syndrom out of the question, and if one >still finds strings <<climb>> the pins by subjecting the >piano to the same kind of conditions and use it otherwise >experiences... (and they do indeed climb) then the crushed notch >theory doesnt hold by virtue of the fact that the condition can exist >despite an obviously non crushed surface. OK. I didn't understand the point of the experiment. It was to demonstrate that strings can climb the pin independent of bridge crushing. And you observed the strings climb the pins on this piano? Did this old beater, on which you shaved down the bridge a bit, have any downbearing? Also, to be clear, what are you calling the crushed notch theory? I get the impression from this post and the last that you're saying that Ron or I are saying there's some connection between bridge notch crushing and climbing strings. I don't want to put words in his mouth, but I believe that Ron is saying that strings don't climb pins - period. The notch edge is receding from the string (at least in dry weather) because it has been crushed. This gives the appearance that the string has climbed the pin because you can tap it down at the pin into the crushed portion of the notch. But the string hasn't lifted itself completely clear of the cap across the entire width of the bridge. When you say that strings have climbed pins, do you mean that there is no contact between string and bridge at all over the width of the bridge? >Pictures... grin... yes this would do a lot of good. I'd get accused >of faking them by those who have already decided whats going on. Perhaps. But it might convince others on the fence, or it might convince the skeptics to get out their feeler gages and see for themselves. >Those >same used about 2 minutes to discount Dons video without even having >seen it. I don't remember anyone discounting Don's video. Did I miss something? > Besides... we all do these kinds of things for ourselves yes >?? I'm perfectly content to put my bit out and let whomever check out >what they want to and draw their own conclusions. > > >One final note. > >The whole line of reasoning Ron N lays out lives and dies upon the >existance of >negative bearing when the string is off the cap. Alls one has to do is find a >case of strings off the surface of the bridge while at the same time >finding plenty >of positive bearing. I believe he did say that he doesn't believe any piano that has positive bearing could have strings off the bridge. He also seemed receptive to being proved wrong. Anyone with a feeler gage (and a downbearing gage, I might add) can do so. No one has spoken up yet. > This is easy to find. New piano prep work shows this as >conclusively as one could ever ask. I thought so too until we had this discussion. Now I'm not so sure. As I indicated in a previous post, one day soon I'll try to go look at some unprepped new pianos and see what I find. I know from experience in new piano prep that I can tap strings down at the pin and see a definite downward movement, and hear a difference in the tone. But if what Ron is saying is correct, then what I'm seeing is a local effect at the pin. I'm not actually tapping down the entire portion of the string over the bridge cap. If I were I should be able to put a feeler gage under the string in the middle of the cap (not at the pin). So, we'll see. > As far as I can see, Ron has simply described one >of the many things that can happen to a piano as it ages. But this does >not amount >to far reaching grounds for claiming the uselessness of string seating. >Not by any >means. > >Cheers >RicB I also don't think he said that string seating was useless. I think he said that it was temporary. On the subject of experiments - as I see it there are three things to look at: 1. Resistance of the string to movement along the pin as the bridge moves relative to the pin. 2. Downbearing load on the notch edge. 3. String vibration contribution to notch crushing, if any. So, I would propose three experiments that would attempt to isolate these three components: 1. String on a bridge with typical bridge pin angles, typical side bearing, and no down bearing, or even slight negative bearing so that when the bridge grows, bearing will not become positive. Subjected to no string vibration. Subject this to humidity cycling. 2. String on a bridge with typical bridge pin angles, but pins located such that there is no side to side offset of the string over the bridge and hence no sidebearing, with typical downbearing. Subject to no string vibration. Subject this to humidity cycling. It seems that you could use vertical pins here, but in case there's something happening due to the string wanting to bow over the bridge and the typical bridge pins wanting to force it down flat, then it might be safer to use typical bridge pin angles. 3. To investigate the effects of string vibration alone is a little trickier. Perhaps the setup in number 2 but with no downbearing. Subject this to string vibration. One potential problem here - is the arrangement of two bridge pins having typical angles, but no side to side offset, clamping the string down in a realistic enough way for this test to be meaningful. Thoughts on this? Phil Ford
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