><< Also, FWIW, I recently ran a test on a sample bridge section to see what > happens to bridge pin height during humidity swings. Cooked in a fishing > rod case with a DC heater rod for three days, the average pin height above > the bridge cap measured 0.126". After three days in a plastic container > with an open bowl of water, average pin height was 0.117". Better not file > those pins too low in the winter. > >> > >Ron: >Sorry I didn't get to this in my other note. This is very interesting. What >do you attribute this to, wood shrinkage or pin shrinkage? Or both? By the >way, I thoroughly enjoy your responses. I have a lot to learn yet, thank the >gods, or this business would be become tiresome pretty rapidly. >PR-J Hi Paul, Easy, the pin is tightest at the bottom of the hole from the moment of insertion since it's had the least length of pin driven through it down there. Also, since there's little to no leverage stress on it down at the bottom, it stays tighter. The pin doesn't grow, naturally, but the bridge changes height with humidity swings and the bridge cap slides up and down the pins as it does. That is, as I see it, the cause of a lot of bridge top grooving (think of the pressure necessary to push that tensioned string up the pins against a 20° angle (both ways), including the friction of pins against string, and the resistance from the increasing tension from stretching the string with the increasing down and side bearing angles. It's kind of scary, and makes the pins loose too by springing them and compressing the supportive cap at the top. Pull some old bridge pins and take a look at the egg shaped skid track where the string rode it. Note that the skid track is taller than it should be for a tangent contact between two cylinders, then picture the string riding the cap up and down the pin with the seasons and wearing just such a track as the cap is grooved more with each wet cycle letting the string go a little further down the pin with each dry cycle. It's nanopinology. Ron N
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