>Phil - > >Thanks for taking the time to pursue the experiments. I will try to >replicate them. A few comments: > >Part of my own soapbox, so to speak, relates to the way measurements >are taken with Lowell, though it would likely not alter your main >observations. There are a number of ways the gauge readings can be >misread, but that's mostly a different discussion. Perhaps we can have that now. What are the ways that the readings can be misread? > Inaccuracies not withstanding, it might be interesting to take >additional readings during the experiment, to see if measurable >change in bearing occurs. It might be. The strings I chose for the little experiment were in different sections of the piano. Lifting a longer string would presumably cause less increase in downbearing, making that string a bit more reluctant to move back down to the bridge than a shorter string having the same initial sidebearing and downbearing. > >I recently had occasion to measure bridge pin angles. I found a >useful visual aid, as follows: using a needle and a very small (but >strong magnet), I apply the magnet to the front or back of the pin, >then attach the needle to the exposed (non-string) side of the pin. >A little care making sure the needle lies flat against the pin, and >taking reading with whatever tool used is much easier. Thanks, I'll give it a try. Phil Ford > >>>If we want to try to establish which of these factors is >>>contributing to bridge or pin damage then I think we need to come >>>up with some experiments which attempt to isolate the various >>>factors. > >Exactly. Thanks again > > >David Skolnik > > > > > > > > > >At 11:39 PM 4/24/2005 -0700, you wrote: >>>....... >>>Pictures are much easier to fake than math and logic, and so are >>>going to be of no use. Something this supposedly common and >>>obvious should be reproducible. If strings get up and stay up pins >>>against positive downbearing, offset angle, and pin angle while >>>people are playing the piano continually until the tuner can come >>>and tap them back down, it ought to be dead easy to pull them up >>>the pin and make them stay there any time you like. I don't see >>>how they could be kept down. The feeler gage can prove it >>>happened, and playing the thing for a while and trying the gage >>>again will prove that strings stay up pins. I'll most definitely >>>attend the convention class where that is demonstrated. >> >>I had had the same thought about lifting the strings up the pins >>and seeing if they would stay there. It was a matter of making >>time for this experiment. So, today I tried lifting up strings on >>a couple of subject pianos at the shop. >> >>I tried this on two pianos (hardly an extensive sample, but a >>start). A little background info - I checked bearing with a >>Lowell gage. The feeler gage that I used was the thinnest that I >>had available, which was 0.004 inch. To begin I checked all >>strings at the bridge cap to see if I could insert the feeler gage >>under any string, anywhere along the string to bridge contact area. >>I then tried to select two or three sample strings in different >>sections of the piano to attempt to lift up. I checked around >>randomly with the downbearing gage trying to find strings that >>seemed to represent the lower end of the downbearing range for >>their particular section of the piano, thinking that if a string >>were to stay above the bridge when lifted up, then a string having >>a lower amount of downbearing might be less likely to seat itself >>on the bridge due to playing (string vibration). But I also >>insured that the subject strings had positive downbearing. I then >>lifted up the chosen strings at the front and rear bridge pins with >>a stringing hook. I checked with the feeler gage to see if there >>was a gap between string and bridge cap anywhere along the bridge >>cap - string contact area. For the subject strings, I then >>measured as accurately as I could with strings and bridge pins in >>place, the sidebearing angle and the bridge pin angle. Note that >>measuring bridge pin angle from a little stub of bridge pin >>sticking up from the bridge is not easy, so bridge pin angles >>should be taken with a grain of salt. >> >>First subject piano: A 1958 Baldwin SD-6. Original strings as far >>as I know. Bridge and pins in very good shape. Strings showing a >>little bit of oxidation. >> >>Initial check with the feeler gage indicated no gaps anywhere. I >>then selected three strings in different sections of the piano to >>lift: >> >>String 1. Sidebearing angle 8.5 degrees. Bridge pin angle 15 >>degrees. Tried lifting this string but the feeler gage showed no >>gap after attempted lift. >> >>String 2. Sidebearing angle 8.5 degrees. Bridge pin angle 9 >>degrees. When I lifted this string it stayed above the bridge. I >>could insert the feeler gage beneath it. So, this seemed to >>indicate that my calcs back in the early days of this thread, about >>a string being able to stay above the bridge in a static situation, >>were not completely fictitious, which was reassuring. After >>general banging on the piano and pounding on this note a couple of >>dozen times there was no longer any measurable gap. I tried >>tapping down the string but didn't notice any substantial down >>movement. >> >>String 3. Sidebearing 13.5 degrees. Bridge pin angle 11 degres. >>When I lifted this string it stayed above the bridge. I could >>insert the feeler gage beneath it. After general banging on the >>piano and pounding on this note a couple of dozen times there was >>no longer any measurable gap. Tapping down the string showed no >>substantial down movement. >> >>Second subject piano: A Steinway B. New bridge cap and fairly >>recently restrung, so everything was in pretty good shape. >> >>Initial check with a feeler gage indicated no gaps except on the >>back side of the bass bridge in certain spots. The strings were >>visually above the bridge at the rear pin on some notes on the bass >>bridge. A check with the downbearing gage indicated small overall >>positive downbearing, but slight negative bearing on the back side >>of the bridge. >> >>I tried tapping down a couple of strings in this area of the bass >>bridge, so that they were against the bridge at the rear pin. I >>then did the general pounding and observed that they were still >>against the bridge. >> >>String 1. Sidebearing 8 degrees. Bring pin angle 8 degrees. When >>I lifted this string it stayed above the bridge. I could insert >>the feeler gage beneath it. After general banging on the piano and >>pounding on this note a couple of dozen times the string was still >>above the bridge and I could insert the feeler gage beneath it. >> >>String 2. Sidebearing 11 degrees. Bridge pin angle 14 degrees. >>When I lifted this string it stayed above the bridge I could >>insert he feeler gage beneath it. After general banging on the >>piano and pounding on this note a couple of dozen times there was >>no longer any measurable gap. >> >>The conclusion from the limited sample was that it was possible for >>the string to be above the bridge, but it seemed to be for >>situations where the bridge pin angle was low enough. >> >>> >>> >>>>>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. >>> >>>As I continue to point out, even under positive bearing, the notch >>>edge will still be below the string after it is sufficiently >>>crushed by cyclic bridge movement. >> >>Right. I think I was agreeing with that. >> >>> >>> >>>>I also don't think he said that string seating was useless. I >>>>think he said that it was temporary. >>> >>>I said it was temporary, and I said it didn't fix the problem, >>>because the resulting tonal problems are almost entirely from >>>loose bridge pins.. >>> >>>>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 >>> >>>It isn't conclusive, since I can't know the piano's entire service >>>history, but de-stringing a bridge, I typically see more pin and >>>notch damage on the speaking side. I have no way to determine >>>whether this is from play, front bearing angles, or seating of >>>strings. >>> >>>Ron N >> >>I've noticed the same thing. If we want to try to establish which >>of these factors is contributing to bridge or pin damage then I >>think we need to come up with some experiments which attempt to >>isolate the various factors. >> >>Phil F >>_______________________________________________ >>pianotech list info: https://www.moypiano.com/resources/#archives > > >_______________________________________________ >pianotech list info: https://www.moypiano.com/resources/#archives
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