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. Inaccuracies not withstanding, it might be interesting to take additional readings during the experiment, to see if measurable change in bearing occurs. 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. >>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
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