Ron and list, Ron writes; >Hi all, I've got one for you. >Fresh rebuild... new agraffes, new brass counter bearing bars, new strings, >high expectations. Result: three strings *ping* and *squeak* through the >agraffes when tuning... a couple in the bass, and one in the low tenor. I >see no apparent reason for the noises, and Protek doesn't seem to slick the >problem away. It isn't really a problem with tuning or general tone >production, but it's one of those annoying things that I think shouldn't be >there without explaining itself, which it so far refuses to do. So what the >heck is it? Ron, we've had this happen in the past with rebuilt pianos also. The most likely culprit is poorly shaped agraffe holes. We have been reshaping all agraffe holes for at least five years (for new and reused agraffes). Many agraffes, including examples from manufacturers who consider themselves to be at the cutting edge, have a mid section of the string hole which is straight sided. This has disastrous consequences for tonal clarity. Take a few new agraffes, cut the top section off through the center line of the holes. Examine the 'half holes' which remain with a 3D microscope. You may be surprised at the lousy shape masquerading as a string termination point. If you haven't a 3D microscope handy, I haven't either, you can use the 50 mm lens off your SLR camera. These make great looking glasses. Our latest agraffe string hole profile cutter comes in the form of a centre drill with a 1.6 mm pilot hole. The drill is specially shaped to an included angle of 20 degrees (the taper slopes away at 20 degrees from the axis of the drill), with a tiny radius leading from the taper to the pilot tip. We use a depth stop to ensure that the 20 degree taper terminates just before the center of the agraffe. The string hole is reshaped with the special center drill from both sides to form a profile which appears as a sharpened inner doughnut ring. The next thing you'll be thinking is that the string might quickly destroy this wonderful termination point we have created. Yes there is a risk, but provided that the string approach angle to the agraffe is not excessive (I prefer to see 10 degrees and definitely not more than 15) the hole will survive if the piano is not tuned too frequently. We also ensure that the counter bearing bar or felt is positioned 20 mm from the center of the agraffe. Long approach lengths here, like long front duplexes in the higher string sections, encourage string noise, while lengths which are shorter tend to marginally restrict tonal quality. We usually substitute the brass counter bearing bars with hardened and nickel plated steel profiles. Ron E. Overs Sydney, Australia Email: sec@overspianos.com.au Website: www.overspianos.com.au
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