jimialeggio5 at comcast.net wrote: > ROn and Dale, > > I understand and am on board(no pun intended) regarding relative crown stability > of pianos with RC&S boards.. > > Let me go back and try to be more clear on what my questions were. Here are 2 > questions, and I'll reference my original statement/question. > > 1-The point of my copy here: > > "I'm doing RC&S boards...5% is not in my repertoire. For downbearing > measurement, > I'm shooting for around 7-7.5%mc. Both yourself and Ron seem to be saying the > crown of an RC&S board is not variable at different mc's. I'm chicken and will > have to prove that to myself before I trust it." > > was one of procedure. > > So my question reflects this procedural issue; > > IE, Is the stability of the RC&S crown such that (in an RH variable shop) mc of > the board, when taking downbearing measurements, is not important and verifying > mc with some mc reference is unnecessary? You have relatively little compression in an RC&S panel, and the rib set is stiffer than in a design that needs panel compression to form and maintain crown, so the unloaded crown won't change nearly as much in an RC&S assembly as it does in more conventionally constructed boards with high panel compression and more flexible ribbing. I don't know of anyone even considering the MC of a more conventionally constructed board when they set bearing. They just wedge the sucker down until it quits moving, and press on. Trouble is, you can't do that with RC&S boards, because the spring rate is much flatter and much higher in an unloaded state. > IE. are you saying that measurements of crown, to verify (for > future use), what your as-built loaded crown deflection was as compared to your > designed loaded crown deflection, can be taken without regard to the mc of the board at that > point, because of the stability of the RC&S crown. Not entirely *without regard*. Nothing is entirely automatic and responsibility free. How stiff is the rib set? What sort of feathering have you used? What was the MC at ribbing, and the MC now? Are you using an adjustable plate height system? Vertical hitches? What's your downbearing target range? > Hope my question is clear-er-er > -- > Jim Ialeggio Personally, I haven't paid a lot of attention to MC levels when I set plate height on my boards and haven't had any disasters as a result. I have done final small adjustments of plate height as necessary, and under full string tension, to accommodate misguestimates. This is, I think, allowed by the committee. <G> Ron N
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