> > The owners are concerned about the plate having fine cracks that > might > > not show up to the eye. It seems like a valid concern to me. Ken, I'll bash this one just a bit more. I think a metallurgist would guide you toward magna flux on this one. Radiography (x-ray) is a wonderful nondestructive test for weld metal because you can see any lamination, slag, impurities, pinholes, undercut or other gremlins that infect welded steel. Cast iron is full of impurities, air pockets and all the things that an inspector uses radiography to detect. (That's why it's iron instead of steel.) It would be very difficult to detect any minute cracks with all the other junk that would appear in the x-ray. Industrial magna flux is specifically designed to detect cracks that are undetectable even by x-ray. It uses metallic particles suspended in a photosensitive liquid. When subjected to a strong magnetic field, the particles arrange themselves around the line of demarcation that interrupts the flow of electromagnetism. When examined under ultraviolet light, the imprint of the magnetic field is readily apparent and any cracks are obvious. PROBLEM: After you detect one or more minute cracks in the plate, how do you determine if the crack(s) were a result of the fall? As cast iron cures, it generally develops stress cracks around areas of dramatic changes in thickness - say where a strut meets the plate. This is a natural result of the molten iron cooling at different rates, thus the thick part contracts at a different rate than the thin part. So is it fall damage or have the cracks been there since it came out of the mold? I have to go with David on this one. If all strings are still in tune and will hold, and you can't see any cracks, it's probably OK and your inspection will be as accurate as any test you may perform. Here's an old race car tip for the real perfectionists: Cast iron may be stress-relieved by grinding (with a die grinder) any casting flashing, mold parting lines and/or other irregularities smooth and flush with the area around it. Also, radius grinding the areas where struts blend to the plate, etc. I've done this on many race car engine blocks, but never on a piano plate. But then, I've never revved a piano over 6500 RPMs. Danny Moore Houston Chapter
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