<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <meta content="text/html;charset=ISO-8859-1" http-equiv="Content-Type"> <title></title> </head> <body bgcolor="#ffffff" text="#000000"> Hi Phil, and others.. Since your last reply included so much of my previous one... and it gets like reaalllly long :)... I'll just snip out a few important points to answer and/or get clarifications on. ----------- First ..... Calculating the pressure on the bridge In order to get a realistic picture of how the bridge gets indented from the clamping of the pins in the face of the bridge surface wanting to rise there are several points you are going to have to get cleared up, strikes me as quite a bit more complicated then what has been figured so far.  A few points are : 1: The intial compressive stress is 1500 psi. But as the wood starts to compress its resistance to further compression is going to increase yes ? It may take 1500 psi to start the indentation, but it will take more to deepen it. So you need to know what that gradient is and figure it in 2: I dont think discounting any lessening in the pin angle due to the hole straightening a bit is a good idea myself. At least not until that is first quantified adequately. 3: You need to know to what degree the pins are actually being pushed upwards, and to what degree they will drag the strings up with them. 4: The maximum initial pulse a string has for any blow hits the bridge in an upwards motion. Very much of the strings energy is transfered then. How much upwards force does this supply.  It is my contention that this will tend towards an equalization of whatever situation is at the bridge notch. So if there is more pressure on the bridge then usual due to the wood taking on humidity, playing the piano will tend to equalize that by pulling up at the string. 5: I'm not so sure ignoring the downbearing is such a good idea either. The downbearing force itself may be neglegible, but perhaps the angles themselves are more important.  That said,  an un pinned bridge with positive downbearing will experience indentation also... so downbearing is in the picture me thinks. 6: The general affect of the soundboard / bridge vibrating with play on all strings/notches. What amplitude of vibration does the soundboard have, to what degree is it always in phase with string vibrations, what happens to the unplayed string/notch condtion when the soundboard is put into near maximum amplitude ? What happens when the soundboard starts to move downwards in its first pulse, pulling the strings afterwards ? 7: How does the longitudinal vibration of the string effect all this ?  The bridge will be pulled and pushed at as well as yanked upwards and then to a lesser degree downwards. If the string breaks the friction of the pin in one direction, it is fairly free to move slightly in any direction. That first upward yank will also be a forward yank. Some of this might sound a bit fetched.. but I doubt seriously anyone has looked closely enough at these along with probably a lot of other things that  should nee factoring in if one is to arrive at a figure of just how much friction must be overcome and by what component at any given moment for the string to climb up the pin a tad.. ----------- <pre>--I think most of us know what Ron is saying, and he is wrong. That >is to say it is wrong to say this is the one >and only, or even primary reason for the strings finding themselves >detached from any portion of the bridge. >Indeed, the condition Ron describes can occur. But there are other >conditions that can occur simultanously with strings >not fully in contact with the bridge. What conditions would those be?</pre> As I've said several times now, strings not fully in contact with the bridge can occure in the face of positve bearing at all points on the bridge. Your own limited experiment which you just shared served to show at least that much. A more thorough testing of many pianos will show that upon pulling up the strings and playing afterwards you will still be able to get your feeler gauge under the string on some. And some of these will measure positive bearing even at the notch. I got introduced to Rons reasoning some 6 years back and immediatly question his postulate strings needing seating only happens when there is negative bearing in some sense or another. So through out that time I have taken the opportunity to check his claim out, and I find it simply doesnt hold. ------------------- <pre>Clearly many many many >technicians have found unmarked bridges on brand new instruments >with plenty of downbearing whilst still finding strings in need of >being tapped down. OK. Let's say that they have. > And just as clearly many many many technicians can find this exact >same situation in pianos that have been used for >a few years. Are these pianos ones that the techs mentioned above found with strings needing to be tapped down that didn't ever get tapped down and so are still above the bridge? Or are they pianos on which the strings were tapped down and with time have climbed the bridge pins? ></pre> Given the claim that the dynamics of the system force the pins downwards into their clamps (bridge pins) I dont see how this question comes up. If on the other hand you reject that the dynamics of the system necessarilly move the strings downwards, then you undermine a very large chunk of Rons <<theory>>. But to answer directly,  techs find this in both cases. Sometimes with positive bearing over the entire surface of the bridge, sometimes not. -------------- (Phil querries..) <pre>I'm not sure what you mean by positive bearing over the entire surface of the bridge surface. Do you think there could be positive bearing on some points of the bridge surface and negative on other points? I look on downbearing as a yes/no thing. Either this string has positive downbearing on the bridge or it doesn't. Phil F</pre> This is central to Rons argumentation... that tho there can be overall positive bearing, the indentation at the notch is below the string line (from top of bridge to front termination), hence negative bearing at only part of the bridge.  In the case where this actually is the situation, then of course any string seating will be a very temporary affair. No argument there. Cheers RicB </body> </html>