>I've always been curious why people use wedges to prestress the board. Because it's easy, cheap, simple, safe, quick, reasonably predictable, and adequate. > Why >not use go bars along the bridge line with which you could actually set the >amount of load you were putting on the board--not to mention distribute the >load in a more controlled way. Because it's harder, more expensive, more complicated, less safe, more time consuming, not predictable without some R&D to determine parameters and methods (and maybe not even then), and wedges are adequate. >By doing this, you would then be able to >see how the board reacts under 750, 850, or 1000 lbs and set the bearing >based on where you wanted the board to end up. Though the effect of >various loads can, apparently, be precalculated, I would think there would >still be some variability. Yes, there is still some variability, as there will be with any method. That's where judgement comes in. The question of using go bars for loading boards is best answered by making up some bars and running some tests with your bathroom scale to see what it takes to produce x pounds per bar at a given difference between bar length and clamping distance, with different size and length bars. Then determine what a further millimeter of soundboard deflection does to your bar pressure calculations and see if this is even possible without spending three weeks setting up each soundboard. If you want high tech, small pneumatic rams with individual regulators clamped on bars over the rim would be quicker, more accurate, and more reliable. But that's not an accurate representation of what the strings are going to do, any more than the go bars would be, so it doesn't look to me to be an improvement over wedges. Ron N
This PTG archive page provided courtesy of Moy Piano Service, LLC