Hi John, Ambrose Beirce defined apology as "laying the groundwork for a future= offense". With this in mind, and looking toward the future, I'm reluctant= to accept apologies where there was no offense. This being the case, I'm= returning your apology (unused) so you may save it for a more worthy cause. Doggone you John, I was hoping to get cheap answers without having to do my= own R&D. Now I'm going to have to go out in the shop and try your= experiment for myself. <G> I can see where the "stagger" and resulting side= bearing would have some bearing (sorry) on the phenomenon as it would= vector the net bearing more toward the horizontal. With little to no side= bearing, the net bearing vector would be vertical, straight down on the= bridge. Maybe there's still hope of clarification. Mike Imbler posted on= another topic stating that he was a mechanical engineer. Mike help, please!= Is the coefficient of friction between music wire and copper plated mild= steel high enough to account for this phenomenon with the forces and angles= involved here in pianos? In other words, does the math fit the model? What= is the high limit of angle at a given tension before the string slides on= the pin?=20 While Mike is deciding whether or not to play, I have more questions. A hard hammer blow (from below) will cause a string to slide up a bridge= pin. We seem to have a consensus on this one, yes? Since the hammer blow= isn't delivered anywhere near the bridge, isn't it the wave in the string= caused by the blow that propagates down to the bridge that does the deed?= Isn't the excursion of a string above the rest position balanced by an= equal (average-diminishing) excursion below? Why, then, doesn't the= excursion below the plane pull the string back down, especially with all= the help it's getting from down and side bearing????=20 Lastly, how would a string stuck up on a bridge pin cause a false beat in= the first place? If it's hanging in there good enough to withstand all the= above mentioned forces to the contrary, the string termination is as solid= as one could hope for! If it's because the bridge pin is loose, we are back= to my original premise that most of the false beats found in pianos are the= result of loose bridge pins and aren't curable by seating strings to= bridges. I don't mean this to look like I'm trying to lead the discussion= with a bull whip, but this is where the logic process brought me. All= enlightenment, clarification, pertinent random musings, empirical= observations and universal=20truths cheerfully entertained. Expectantly,=20 Ron Nossaman=20 <******* History beyond this point *********> At 09:17 PM 4/11/97 -0600, you wrote: >Hi Ron, > >My apologies for misinterpreting your question. I understand now what your= asking, and I have tried a very un-scientific, but possibly enlightening= experiment this evening. > >I am currently doing some work on my personal piano in my shop. I rebuilt= this piano (a Bradbury 5'6" reproducer grand) about six years ago, and it= happened to be my first bridge recapping job. Because of this some of the= bridge pin placement is, well, pretty embarasingly wacky. A few pins are= placed in such a way that there is very little, if any side bearing. The= rest of the job is fine: good downbearing, nice tight well angled bridge= pins etc. I took some strings off and checked bridge pins and found no= *visible* notching in them. > >I got to thinking that this would be a great situation to test if side= bearing played a major role keeping the strings off the bridge. > >Here's what I did: With the piano up to pitch, I simply pulled up on the= speaking lenght side of a couple of strings until they lifted off the= bridge, then let go and watched what happened. The strings that had no side= bearing went right back down to the bridge. The strings that had decent= side bearing stayed up! I did several in the sixth octave of the piano= (this is where the misplaced pins are) and the strings rode up above the= bridge anywhere from 10 to 15 thousandths according to my feeler gauge. > >This little test, while not very controlled, would seem to point to side= bearing, and its attendant friction as one of the major contributing= factors in keeping those suckers up in the air. > >Comments anyone? > >John McKone, RPT >St. Louis Park, Minnesota >(612) 280-8375 > >----------------------------------------------- >>From : Ron Nossaman <nossaman@southwind.net> >Sent : 04/11/97 >To : pianotech@byu.edu >Subject: Re: bridges/seating > >At 08:58 PM 4/10/97 -0600, you wrote: >>Ron, >> >>If you're asking why the string can creep up against the pressure of= downbearing and friction, you need look no further than the impact of the= hammer (on a grand anyway) Especially on a hard use piano. >> >>John McKone, RPT >>St. Louis Park, Minnesota >>(612) 280-8375 >> > > >Nope, nope, not at all. It's quite obvious that a string can be knocked up= hill against tension, friction, or anything else you care to name. You can= here it happening if you work at it. It's quite clear to me how a string= GETS up a bridge pin. I'm saying that it's not possible for it to STAY up= off the bridge, AT REST, against tension and side/down bearing and pin= angle, unless there is something physically wrong with the bridge pin. What= else would hold it up there magically???? David Copperfield plating? There= has to be a real reason for an observable physical phenomenon. I get enough= mysticism and "have faith, trust me" metaphysics from Government.= Demonstrations can illustrate that it's possible (I'm still working on that= one), but I don't think anyone can realistically champion a fix without a= clear understanding of what's broke. Let's talk "mechanism". I'm willing to= accept the notion that this happens only in the context of a rational= explanation as to WHY it is possible. Wouldn't you like to know too? > > > Ron Nossaman > > > Ron Nossaman
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