Hi to all, Ron Nossaman wrote > . . . . agraffe and v-bar damage (averaging iron hardness) is >related mostly to the intensity, both in hours and enthusiasm, of play We maintain two Ds at the Australian Broadcasting Corporation in Ultimo, Sydney. Occasionally, these pianos are tuned up to four or five times per week. We have found that the capo' bars on these pianos deteriorate more rapidly than for other high-use pianos which are tuned perhaps four times per year. We blame the 'cutting' action of the wire during tuning, especially when the bars are soft. This deterioration also leads to the development of string noise. When the 1986 D was rebuilt again last year, after being reshaped the capo' and duplex bars were hardened. The damage sustained between the 1993 restring and last year on the (radius reduced but unhardened) bars was incredible. >whereas the bridge pin damage is related to both the intensity of play, and >the number and severity of humidity cycles the piano has been through since >the pins were new. I don't see the frequency (no pun, that's the other >thread) or the total number of tunings having a lot to do with either >problem. >I think the total height of the bridge pin groove is related to the >number and severity of humidity swings as the shrinking/swelling bridge >carries the string up/down the pin as the bridge top cumulatively crushes >under the string. The scrub tracks in the front bridge pins are deeper than >those in the back ones (check it out), so I would blame the depth on the >intensity of play. The friction between the front and rear rows of bridge pins (ie. between the string and the bridge wood) will always result in less load on the rear pins when the string pulls through to the speaking length from the back length, and consequently less damage. Further, a higher string offset angle (as it crosses the bridge) and a higher bridge pin inclination angle, will also increase the load on the pin. A string offset of 10 degrees combined with a string tension of 175 pounds will result in a lateral force of over thirty pounds to be exerted on the bridge pin. Tension on bridge pin (in pounds) = [Sin(string offset angle) + Tan(bridge pin inclination)] x (string tension in pounds) I believe technicians tapping the strings down on the bridge is a major cause of damage to string termination points. When we rebuilt the ABC's 1986 D in 1993, the strings had been 'tapped' down previously (by another technician). The string speaking lengths met the bridge wood nearly 3mm in front of the pin (I will publish a slide of this on our web site eventually). Many manufacturers appear to be careless about maintaining a uniform bridge pin angle and string offset angle. We use the same specification for all rebridged instruments, ie. 10 degrees of string offset, and twenty degrees of bridge pin inclination from the vertical. We believe the implementation of these figures will prevent the strings climbing the bridge pins. When drilling the bridge pin holes, we attach a bubble gauge to the drill to maintain the correct angle. When marking out the rear bridge pin offset positions, we use a formatted spreadsheet to calculate the offset measurements. Variables entered onto the sheet include the string gauge, bridge pin diameter and inclination, and the string offset angle. I agree with Ron Nossaman's comment, when he says we should consider the bridge pin condition along with the capos and agraffes. Ron E. Overs, Sydney Email: ron@overspianos.com.au Website: www.overspianos.com.au
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