My, what a bucket of snakes we've opened here. (I've never been bothered by buckets of worm -- they just kind of lie there squirming around. Snakes, on the other hand...) As may be, I'll warn you in advance...if you get bored easily delete this post immediately on to the next one. The crack described by Richard is on the top of the longitudinal strut running roughly parallel to and above the highest string in the bass section. If I read the description of this crack correctly, it is in the strut passing over the tenor strings. The crack started at top of this strut and runs down into the body of the strut. OK. Baldwin does not use any type of horn to transfer any of the string load to the belly structure so this places all of the stress on the longitudinals. These struts run well over the line of stress, i.e., the centerline of the strings. This places the lowest portion of these struts in compression -- gray iron's best feature is its compression strength, and even there it is none too high -- and the top portion in tension and grey iron has very poor tensile strength. By that I mean it is VERY weak in tension. One of the functions of the nosebolt is to keep the struts from bowing up and allowing excessive tension from developing in the top portion of the longitudinal. If the nosebolt is/was loose enough to allow the strut to bow upward, this would allow greater tension to develop at the top of the strut than the gray iron is capable of withstanding and a crack develops. I wouldn't recommend it, but in all probability if the nosebolt could be adjusted so that the strut is brought back down enough to close the crack the piano probably could be tuned without further problems. Yes, it would make me nervous but I think it could be done. How to repair this problem. I have no experience with the 'Lock-N-Stitch' process. I have read quite a lot of promotional literature produced by the company making the things, but I have not actually used the process. So anything I have to say about it is based strictly on my observation of the components and my experience with gray iron. The Lock-N-Stitch' process involves drilling and inserting a plug that is held in place by the geometry of the threads on the plug. In the end any tension placed on the member in question is going to be held by the ability of the threads to bite into the existing iron and hold it in tension. I personally would not trust it to hold in this situation. I suspect the process would work well in the repair of a flat panel that is not held under high tension over a long period of time. I have had good experience with having gray iron welded. The shrinkage rate of gray iron from its molten state to its frozen -- solid -- state is closer to 1% than it is to 6%. The patternmakers rule is about 1010 mm for a 1000 mm rule, or about 1/8" per foot. This is significant in a one meter long longitudinal but not in a 20 mm weld. I am also not enough of a metallurgist to explain exactly why gray iron is so problematic to weld, but the folks I have consulted have told me it has more to do with the amount of carbon in the iron than with the shrinkage of the iron. Iron structures with less carbon -- malleable iron, for example -- can be easily welded even though it shrinks at roughly the same rate as does gray iron. I learned long ago to use the word 'gray' when describing the type of iron used in piano plates. These guys work with a lot of iron castings but few of them use anywhere close to the amount of carbon in them that is used in piano plate castings. So, how to repair Richard's Baldwin. It sounds like it is pretty much all done and it will probably hold. Personally, I would not have used the Lock-N-Stitch process in this repair. I would have veed out the crack, had it welded with one of those nice new welding rods that are supposed to work well with high-carbon gray iron and made sure the nose bolt mounting was solid and that the bolt itself was properly adjusted. His idea of sistering the bar with steel plate is probably good insurance. If anything, I would have pre-loaded the strut by pulling the nosebolt down just a bit to reduce the development of tension along the top of the strut. I would then check the stringing scale to be sure someone didn't get in there and raise the scale tensions significantly and tune the sucker. After all of this, if I still had any reservations about my repair holding, I would fabricate some type of 'horn' that I would mount below the plate to couple some of the stress from the strings directly to the bellyrail/rim brace assembly. The Baldwin has a fairly sturdy structure down there and I could probably transfer a substantial portion of the load to this portion of the framework without introducing any other problems. One last comment about nosebolts. They are used in several ways depending on how the piano structure and plate are designed. As Ron pointed out they are often used to mass-couple the plate to the wood structure of the piano. The most obvious example of this is the bell and bolt arrangement used in the larger Steinway pianos. They do raise the impedance of the plate and reduce the mechanical losses to the plate. I.e., they aid sustain slightly. They are also used to stabilize the plate. As noted earlier, gray iron works better in compression than it does in tension. The nosebolt is often used to keep struts from bowing upward and placing the top of a longitudinal strut in tension. This is the purpose of the nosebolts going through the #1 bass longitudinal strut -- the long strut running along the bass side of the lowest bass string. Without the nosebolt in place these struts do have a lot of flex and can easily break. (Another way to stabilize these long struts is to give them a strong inverted 'T' shape.) And, yes, they are used to control plate ringing. It is often more economical and practical to design a nosebolt system to control ringing and to stabilize the plate than it is to simply add more mass. Simply adding mass to a gray iron casting does not always add strength. In fact, it sometimes will weaken the overall casting. Complex gray iron castings cool at uneven rates. When a very massive section is next to a less massive section a very strong internal stress will be present in the finished casting. Sometimes this stress can be great enough to cause the casting to break even before the intended load is placed on it. A more practical method is to reduce the sections to their practical minimum and use a well-placed system of nosebolts to control both flex and ringing. This, by the way, was the approach taken by the designers of most of the Steinway plates. They are reasonably light weight, do not ring appreciably in practice and are quite stable. You can't ask for much more than that from a piano plate. Regards, Del Delwin D Fandrich Piano Designer & Builder Hoquiam, Washington USA E.mail: pianobuilders@olynet.com Web Site: http://pianobuilders.olynet.com/
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