Even in the rare cases of piano with intentionally designed reverse crown board it still depends on positive bearing load to function. What kinda piano was this that started this thread anyway? Dale ----- That’s right. Anytime you have negative bearing, the strings are pulling the bridge up just as with positive bearing they are pushing the bridge down. If you were to detach the strings from the bridge pins where there was negative bearing they would hover above the bridge. You would have to push the string down to reattach it to the bridge thus the force from the string would be upward. David Love www.davidlovepianos.com Sounds good. I don't understand this though: "that means that the bridge is being pulled up by the strings" in the second case. It was my understanding that negative bearing means the bridge is lower than it should be, causing the strings to be slightly v-shaped rather than ^-shaped. On Thu, Dec 24, 2009 at 11:39 AM, David Love <davidlovepianos at comcast.net> wrote: If you have positive bearing and positive crown then you have downward pressure on the board with residual crown so if you take off the strings the board must rise, i.e. the crown remains positive. Good sign. If you have positive crown with negative bearing that means that the bridge is being pulled up by the strings and to what degree that is responsible for the crown formation you can’t tell until you take off the strings. Bad sign. If you have positive bearing with negative crown you can’t tell whether when you remove the strings the board will rise to show positive crown or not since you don’t know how the bearing was originally set or exactly how far down the bearing is pushing the crown. Bad sign. If you have negative bearing and negative crown that means the board is being pulled up but even with that is not achieving positive crown. Definite burnt toast. Keep in mind that each section of the piano may show different relationships to crown and bearing and, as Ron mentioned, several measurements are necessary across the panel. David Love www.davidlovepianos.com -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://ptg.org/pipermail/pianotech.php/attachments/20091231/9d529e86/attachment.htm>
This PTG archive page provided courtesy of Moy Piano Service, LLC