<html> <body> Fred - I wrote this earlier, before other responses materialized, but it's my daughter's birthday, so I don't have time to edit for redundancy, accuracy or intelligibility.   I'll let you, or someone else do that. At 09:25 PM 4/5/2004 -0600, Fred Sturm wrote: <blockquote type=cite class=cite cite>   I am thinking in practical terms: if one chooses (as I do) to resurface the bridge top, re-notch and repin, should one make a great effort to get the top back to flat? Perhaps not. I will theorize that a curved profile will work just fine, as long as, using the string test, a string run from capo or agraffe touches front of notch before the rest of the bridge top.</blockquote> Fred - Back in the days when this thread was just Tuning Stability, on 3/30 to be exact, I asked you and Mark Cramer what you felt was achieved by planing out the string grooves.  While it might afford you an opportunity to justify the time spent keeping your plane blades sharp, I couldn't see that it would have any tonal effect.  I visualized a string groove that, even if more pronounced at the edges, nevertheless showed some compression across the entire bridge width.  Certainly, any instrument for which you were about to undertake such sort of restorative measures would be expected to have been around for long enough to have developed such indentations.  As such, the groove would provide you with enough of a guide in planing.   If, in your statement above, you are envisioning the intentional introduction of a curvature into the bridge surface profile, I suspect that there are very practical reasons why it would have no greater success than a flat profile, given that, for a variety of reasons, even the latter ends up inconsistent.  Even theoretically, I think you DO want a flat surface, at least at the front, since without that, you have cannot create an angular relationship between string and bridge, but rather a tangential one, which would have its own potential termination problems. <blockquote type=cite class=cite cite>In fact, maybe a mild curvature would be better theoretically, both for transfer of energy and for durability. </blockquote>and <blockquote type=cite class=cite cite>One may be reducing the loading of the bridge a wee bit by removing the curved part in the middle of the bridge.</blockquote> As Tom Lowell explained to me, as far as bridge loading is concerned, the angles created by the straight line, possibly only imaginary, between the front a rear bridge pins, in relation to the front and rear string segments, are what determine the loading.  Anything can be happening on that bridge surface ("to the moon and back" is what I think he said), but the loading will depend on those angles.  I got it after a while.  So planing the curve flat would not, in theory, affect the loading, however, it would, in theory, redistribute that load from the entire bridge surface to the bridge edges, thus increasing the compressive stress at these points, and potentially accelerating the fibre crushing process, whether from downbearing or the seasonal bridge height movement Ron Nossman has described.  I don't see how rounding the bridge surface would affect the transfer of energy, but I can see how distributing the downbearing load evenly, over the entire bridge width could reduce the stress on the notch edge, but, to a degree, that's what happens in time anyway. <blockquote type=cite class=cite cite>How is load transferred through bridge to board?</blockquote> Not sure what you mean. <blockquote type=cite class=cite cite>   Following this general avenue of thought, I wonder what measurement made with the downbearing gauge would reflect the reality of deflection and loading best, given the reality of string grooves in a bridge top (and a likely curved profile). One question that can be addressed is whether and how much the string deflects just behind the notch/pin, which will give a notion of whether front termination is good. But perhaps a comparison of speaking length level, back length level, and measurements with one leg on the middle of the bridge and one on speaking length, and another with middle of bridge and back length, would give a better picture of how much the string is being deflected/how much it is loading the bridge.</blockquote> First, picture a hypothetical string and curved bridge surface, where the bridge deflection looks like a speed bump in a road, and where the front and rear string segments are on exactly the same plane. This theoretical configuration is only enabled by the presence of bridge pins and seated strings. (Without either, the string would simply follow a straight line to the top of the bridge profile.) If you were to zero on front and then measure rear with the gauge, it would read as zero downbearing.  If you measured the bridge string-segment in the traditional manner  (gauge feet spread to just shy of front and rear pins), it would seem to confirm the previous zero reading (again, assuming that front and rear points of curve fell exactly on plane line).  Using either sliding method,  two feet close together or one foot on sounding length, the other on bridge string segment will provide a picture of what deflections are present, <blockquote type=cite class=cite cite>   Anyway, a bit of food for thought. Regards, Fred Sturm University of New Mexico</blockquote> David Skolnik</body> </html>