>Phil writes > > >/RicB writes > >This is simply incorrect. True enough when a soundboard and bridge >/>/become so damaged that there is no positive bearing, or that bearing >/>/is lacking relative to some portion of the bridge surface, then >/>/seating becomes a very temporary fix.... increasingly so with the >/>/amount of damage. But this does not cover the cases when strings >/>/need seating despite positive bearing all around. >/>/ >/>/RicB >/ >If humidity increases and the bridge moves up and the string does >not, then the cap will be crushed locally by the pin. When the >humidity decreases then the cap will move back down and once again >the string will not. So there will be a gap between the string and >the bridge cap at the edge of the notch, even if downbearing is >positive. So, you have a case where the string needs to be seated >despite positive downbearing. I don't see why this case isn't >covered. > >Phil F > >By reverse logic, if humidity increases and the bridge moves up and the >cap does not experience crushing, then the string obviously has moved... >for whatever reasons. I agree. I think that's the crux of this discussion. If the cap material is strong enough (hard enough) then with a humidity increase it will push the string up and the cap won't indent. When the humidity decreases the cap will move back down. The string may or may not follow it, depending on what you believe - another point of discussion. If the cap material is not strong enough (hard enough) then when the cap moves up the string will indent itself into the cap and will not move up. When the cap moves back down the string will not be able to follow it because the angle of the indentation at the edge of the notch is now greater than the angle that the string makes with the bridge, so there is a gap. My calcs show that the cap material is not strong enough. You seem to think that it is. This is where an experiment comes in. > This happens quite a lot actually. If it didnt you >would see severe notch indentation the very first season change... every >time. In actuality newer pianoes usually have only slight indentations, >and much of these are caused by over eager string seating proceedures. What do you call a severe indentation? Ron mentioned a number of 0.011 inch of movement between bridge cap and pin. That's not very much. I would say that an 11 thousandths indentation wouldn't look very severe. I think what is causing the severe indentations is the process of repeatedly tapping the strings down over the years. The bridge goes through some number of humidity cycles which causes an indentation. The tech comes along in the dry cycle and taps the strings down. The next wet cycle the cap crushes some more. And on it goes. So, not only is tapping the strings down a temporary fix, it's making matters worse in the long run. >The whole point of Rons argumentation is that the bridge surface pushing >up against the clamped strings results in the bridge surface being >crushed to the point of forming an indentation that lies under the line >drawn from the strings highest point on the bridge to the front >termination. When this happens there is negative bearing at that >indentation. If on the other hand there IS positive bearing at this >point AND the strings still need seating... his theory fails to explain >how this can be... and indeed claims the condition is impossible. Since, >however, it is clearly observable that this condition DOES exist and >quite frequently... I have to disagree with him :) > >Cheers >RicB As I mentioned in a previous post I think we need some clarification of the terms bearing and contact. If the string is making contact with the bridge behind the crushed notch edge and is coming off the bridge at a down angle, I call that positive bearing with no contact at the notch edge. Are you calling this situation negative bearing? What are you calling positive bearing? Contact at the notch edge? Phil F
This PTG archive page provided courtesy of Moy Piano Service, LLC