Keith Roberts wrote: > Gentlemen, excuse me for butting in, > > I think Ron also writes of bridge pins that push themselves out of the > bridge due to the way they were installed. Not exactly. The point of zero relative movement between the pin and bridge tends to be at about the bottom of the cap, maybe 8mm down. The bridge cap rides the string up and down on the pin with humidity cycles. The bottom of the hole, meanwhile recedes from and approaches the bottom of the pin similarly. This is why bottoming pins in the hole doesn't do anything to "seat" the pins. The next humidity cycle will put them right back where they were. The pins don't advance out of the bridge farther than the bottom of the hole at the driest part of the cycle can directly push them. >When a wear spot on the pin > has developed, the pin could reduce the pressure of the wire on the > bridge as the pin gets squeezed out. Not unless the dry cycle is the driest it's ever been, and the pin is extremely worn. >As the humidity cycles, the job of > setting it back in place has to be done again. Not so. By the time the flat spot has worn that deeply into the pin, the 15lb friction between the pin and string that I keep so hopefully mentioning will have crushed the notch edge below the line between the bridge top and capo. The string is still on the bridge, but the notch has been crushed below string plane. >The pin would also become > loose and setting it the first few times would make the biggest > difference. Setting the pin is making use of that 15lbs of friction between the pin and string that I keep so hopefully mentioning, and pushing the string into the bridge with 15lbs of force, which is at least nominally equivalent to seating the string. There is no acoustic benefit to seating the pin. Turning the pin (as you suggested earlier) to get a fresh surface would eliminate any problems with the pin wear, but the existing damage to the cap is still there, and the false beat or fuzzy tone would still exist (or return with the next humidity cycle). The higher percentage of false beats in the treble seems to > be indicating the smaller gauge wire cuts a deeper mark in the pin. I think that the resonant frequency of the flagpoling loose (and smaller diameter) pin more nearly corresponds to the frequency of the treble notes, producing beats slow enough to hear. The false beat comes from the pitch difference between the vertical excursion of the string, which is solid on the pin, and the horizontal excursion, which is of lower pitch because of the flexing pin. The indication is to press against the side of the pin opposite the string while you play the note and observe that the beat stops, reappearing when the pressure is released. The string is not up the pin by any imaginable means, and even if it were, why does the beat stop when you keep the pin from flagpoling and return when you don't? It's the loose pin that's the real problem. > I think something like epoxy or CA glue to stabilize the pins might > help. It most certainly does. As a less than ideal, but no other reasonable way out fix, I've CAd pins in place, strings on, to very good effect. >Proper replacement of bridge pins might be necessary in some cases > no matter what. A better fix, but I still CA or epoxy new pins in to prevent, or at least delay recurrence. Again, seating strings or pins doesn't fix a thing. It just gives the illusion, sometimes, that something positive has been done. The crushed bridge notch edge and the loose pin are the real problem. Ron N -------------- next part -------------- A non-text attachment was scrubbed... Name: Bgroove2 sm.jpg Type: image/jpeg Size: 115307 bytes Desc: not available URL: <http://ptg.org/pipermail/caut.php/attachments/20100209/87c6c47b/attachment-0002.jpg> -------------- next part -------------- A non-text attachment was scrubbed... Name: Bgroove sm.jpg Type: image/jpeg Size: 94338 bytes Desc: not available URL: <http://ptg.org/pipermail/caut.php/attachments/20100209/87c6c47b/attachment-0003.jpg>
This PTG archive page provided courtesy of Moy Piano Service, LLC