Brian Trout wrote: > A few years ago, a Kimball grand came into our shop to be "reconditioned". > It was about a 5' 10" ? or so, I don't remember exactly. But it was a nice > piano in a lot of ways. One of the places they 'cut corners' was in the > case, and supporting framework. It was amazing to me to see that there were > absolutely no support beams. It was completely open underneath. It was in > my opinion one of the weakest points of the construction. It seemed to have > a pretty nice action, a fair sound, and a nice looking case. But I suspect > it wouldn't be very stable.? My question for you is: Have any of you ever > taken a piano like this and made the appropriate support beams and fit them > to the rim and belly rail? I know it's beyond the scope of most, but I had > thought about doing it if I ever had the piano that might warrant that kind > of modification, whatever it might be. ---------------------------------------------------------------- Yes. We regularly add belly bracing to grand piano rims. But, before you start doing this you need to understand what you are trying to accomplish. First -- except in pianos like the Steinway where special plate horns are provided -- belly braces are not intended to help support string tension. And, while belly bracing often does function to square and stabilize the rim assembly, structurally sound pianos can be built without them. Their major benefit to the piano is actually acoustical, not structural. They both acoustically stiffen and mass load the rim and the bellyrail assembly. In other words, they help to reduce energy losses from the soundboard to the bellyrail and rim. In a piano like the Kimball this can be particularly important since the rim was undoubtedly made of poplar or some similar Select Hardwood. I don't remember what type of wood Kimball used in the belly rails of their pianos. In other pianos of similar construction I typically find poplar. Occasionally I've also encountered spruce and pine. None of these are particularly massive woods. Second, they provide an anchor for any nosebolts that may be desirable. Along this same line, nosebolts are not provided to structurally support the plate. Nor are they put there to make it easier to adjust downbearing. They are there to stiffen and mass load the plate. To raise its mechanical impedance and help reduce energy losses from the strings to the plate. They are also used to prevent -- or at least control -- any spurious ringing and/or resonances that may be present. So. With the above in mind, we're now ready to design ourselves a belly rail assembly. In a piano of this size I'd probably end up with three braces. Depending on the exact shape of the rim they would probably be perpendicular to the bellyrail and parallel to each other. They would be spaced at equal intervals across the bellyrail. That is, if the belly rail were 1350 mm long -- or wide, take your pick -- they would be spaced approximately 337.5 mm apart on center. There is nothing magic about this placement and the braces can be shifted about as needed. For example, we will sometimes try to fit in a couple of nosebolts and there are often a limited number of places where nosebolts can be located on the plate. This will dictate the exact spacing of the appropriate brace. Once the longitudinal braces are in place we will sometimes also place one cross-brace between the straight long side of the rim and the first belly brace. This is used to acoustically stiffen the straight side of the rim -- especially with poplar and/or Select Hardwood rims -- and to provide a place to seat our soundboard cutoff bar. This brace is usually made perpendicular to the straight side and is placed approximately in the center of the straight run between the bellyrail and the start of the bass curve. Its exact placement is often determined by the placement of the soundboard cutoff bar. All of our belly bracing is installed the same way. We fit the bracing to the rim and/or bellyrail snug, but not excessively tight. We coat the ends of the new braces with unfilled epoxy and allow it to soak in for several minutes -- recoating until no more will soak in. We then fill the remaining epoxy with wood dust until it is the consistency of very heavy gravy. Just barely brushable. We put one coat of thickened epoxy on the ends of the new braces. We mark and clean the rim and bellyrail where the braces will go and coat the surfaces with the thickened epoxy. We spread the rim apart slightly using spreader pipe clamps and slip the new braces into place. When the spreader pipe clamps are removed the rim will come together slightly and squeeze out any excess epoxy. Clean everything up and let it cure. As a final step we put in two diagonal 1/2" dowels at each butt joint on both the top and the bottom of each brace. (Did I mention that all of this work is done with the soundboard removed? It is.) There is no reason why a remanufactured piano like the Kimball you describe cannot perform as well as most any so-called High-End piano. In fact, the grand pianos that Kimball was building just prior to their closure were only about 5% away from being excellent pianos. With just a small amount of tweaking to their acoustical design and structure they could have been outstanding pianos in spite of their very reasonable prices. We currently have in our shop a "Noname" 175 cm (approx. 5' 9") grand that will easily hold its own alongside any Model M or Model L Steinway. And this instrument was not built nearly as well as most of the Kimball's I have encountered. Regards, Del
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