Folks, Sorry I wasted bandwidth. This was an old question from David Love that I saved. Looks like I found it again by accident and this time decided to respond. Please disregard. Greg At 06:17 PM 3/7/2006, you wrote: >David and others, > I understand your questions and they are >good ones. Perhaps my answer is simpler than >anyone is looking for but ........ The board is >designed in such a way as to be in direct >opposition to the downward force of the >individual and combined force of the strings. >There isn't any magical relationship that I'm >aware of as a carryover from a CC setup save that >the opposing spring of the board is still in >direct opposition to the strings. It seems to me >that the beauty of the RC&S system is the >achievable predictability of the result not >necessarily the added potential in it's strength >capabilities. Just because the capability exists >does not necessarily mean it is exploited. > Consider that in many cases where a RC&S >system is used it is also coupled with the other >design elements of an adjustable plate support >system and a roll pin type arrangement both of >which assist in setting a micro-adjustable down >bearing. This is a real part of the beauty of >this overall plan. Taken alone these two would >serve to provide a much better result even in a >CC board system since it is so fully adjustable. >The preference for RC&S in my mind seems to be >one of longevity. Since the compression / tension >relationship is mostly or wholly residing in the >ribs the panel is far less likely to crack over >time resulting in a much happier customer in the >long run not to mention the possible elimination >of the killer octave scenarios and bridge roll >scenarios that we all know and love. > Please know that I am somewhat a >neophyte in this and my opinions mean very little >if anything at all. This is all just my current >take on the subject and hey, you asked! > >best, >Greg > > >At 11:03 AM 2/22/2006, you wrote: > >There is another issue to be raised. How should one match the scale > >tensions and anticipated downbearing angles to the rib scale. There are > >choices to be made. I presume that you want a certain amount of deflection > >of the soundboard assembly and that given a certain scale with a certain > >downbearing load, you can calculate the panel assembly stiffness and preset > >crown (in and RC&S board) to achieve that amount of deflection. But there > >are yet various ways to achieve that amount of deflection. For a given > >assembly you could increase the scale tension and lower the downbearing > >angle or decrease the scale tension and increase the downbearing angle. You > >can design an assembly with greater stiffness to go with a lower scale and > >greater downbearing or a lower stiffness to go with a higher scale and less > >downbearing, for example. Each combination, I presume, will produce its own > >unique tonal characteristics and, probably, require a hammer of different > >density and/or mass. Those of you who are designing boards, how would you > >characterize your goals and why?. If we can produce a RC&S board that will > >be able to accommodate any particular variation in load, what is so magical > >about the .5 - 1.5 degrees of downbearing that seems like it came about > >mostly due to the limitations of compression crowning. Further, in an RC&S > >board, what combination is most likely to give the general tonal > >characteristics of your successful CC board. And let's allow ourselves to > >speculate even if we haven't actually built each variation. > > > >David Love > >davidlovepianos at comcast.net > > > >-----Original Message----- > >From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf > >Of Overs Pianos > >Sent: Sunday, February 19, 2006 3:15 PM > >To: Pianotech List > >Subject: Re: laminated ribs > > > >Richard, > > > >The downbearing (vector) force on the sound board > >is equal to the SIN of the angle of deflection > >times the string tension. > > > >If there was absolutely no down bearing angle, it > >follows that there would be no downbearing force. > >The SIN of zero is zero so the string tension > >vector component force would be zero. > > > >If the down bearing angle was 90 degrees, with > >the speaking length segment parallel to the board > >and the back scale heading vertically downwards, > >the down bearing force would be equal to the > >string tension, ie. the speaking length segment > >would be contributing nothing to the down bearing > >force, while the back scale segment would be > >contributing its full string tension. The SIN of > >90 equals 1.0. String tension X 1.0 equals string > >tension. You can see how it all works. > > > >So if you have 160 lbs unison string tension with > >a downbearing angle of 2 degrees, the downbearing > >vector force for this unison string would be; > > > > Downbearing = 160*Sin2.0 > > > > Downbearing =5.583 lbs > > > >The downbearing force for the whole note would be > >3 X 5.583 if the note was a trichord, at 16.75 lb. > > > >If you are using an excel spreadsheet for your > >calculations, remember that the downbearing angle > >will need to be converted to radians. > > > >Yes, there is a large variation in what people > >believe is an appropriate level of downbearing. > >If you measure a few pianos around the place > >you'll find that there is a lot of variation in > >the downbearing angle also. > > > >The 2 degree figure you quoted I would consider > >to be too high for a real world piano. > >Bösendorfer have typically set their pianos with > >angles approaching 2 degrees strung. This is a > >little higher than I would feel comfortable with. > >When Ron N was here a couple of years ago we > >looked at our no. 5 with a Lowel gauge and it > >measured almost right on 1.3 degrees over the > >whole piano. This yields a total downbearing > >force on our no. 5 of 427 Kg (941 lb). I wouldn't > >recommend these figures for an older or weaker > >panel but it works just fine for our I-rib > >design. Setting the downbearing angle is a > >balancing act between how much the board will > >sink and how much force we wish to apply. > > > >When looking at a given piano, I suggest that you > >set up a spreadsheet to calculate the downbearing > >force you are planning to set up per rib. Note > >also that setting an unstrung angle of say 1.5 > >degrees won't result in a downbearing force of > >tension X SIN(1.5). Its the resultant string > >deflection angle when the piano is at pitch and > >the board has stabilised (sunken to equilibrium) > >under load which will determine the actual > >downbearing force. So you need to make an > >educated prediction on how much a board will sink > >under tension to get an idea of the resultant > >downbearing force. > > > >A common scenario with new pianos is for techs to > >measure a down bearing figure which on the face > >of it looks OK, but very often the sound board > >has sunken to a state where it is pushed almost > >completely flat by the down bearing angle which > >was set into the piano. In these instances the > >board is too weak for downbearing loads which are > >being applied or the unstrung angle wasn't set > >properly. Either the downbearing unstrung angle > >should be reduced or the board strengthened to > >withstand the setting angles to which it is being > >asked to resist. So often technicians will look > >at a sound board and declare that it is fine > >because the downbearing angle measures some > >wonderful figure. But if the board has been > >pushed inside out before the customer's ink is > >dry on the cheque, things ain't too good, > >regardless of what the downbearing gauge might > >indicate. > > > >Get an accurate downbearing gauge and a thread > >length for looking at crown, and measure a few > >pianos old and new. You'll develop a picture of > >what's happening. > > > >Ron O. > > > > >Please correct if this is entirely wrong... but > > >I thought that since the string was being > > >measured in terms of its tension (pounds) one > > >could simply the problem as a like sided > > >triangle with half the pounds on each leg. Since > > >the measurement is taken in the deflected > > >condition... you have basically the hypotenus > > >and all angels of a right angle triangle > > >available to figure the amound of deflection.. > > >pounds in this case. So 160 pounds with a 2 > > >degree deflection at the bridge yields > > > > > >Sin 1 x 80 = 1.396192515 lbs downbearing, > > >which is 1.745 % of the string tension. > > > > > >er... yes ?? > > > > > >RicB > > > > > > > > >------------- > > >> So knowing all of the above, what is the equation that will calculate > > >> an approximate string bearing load under the conditions I describe? > > > > > >Beats me. I use the SIN(RADIANS(degree measurement))*tension > > >per unison, and add them up in my spreadsheet. > > >_______________________________________________ > > >Pianotech list info: https://www.moypiano.com/resources/#archives > > > > > >-- > >OVERS PIANOS - SYDNEY > > Grand Piano Manufacturers > >_______________________ > > > >Web http://overspianos.com.au > >mailto:ron at overspianos.com.au > >_______________________ > >_______________________________________________ > >Pianotech list info: https://www.moypiano.com/resources/#archives > > > > > >_______________________________________________ > >Pianotech list info: https://www.moypiano.com/resources/#archives > >Greg Newell >Greg's piano Forté >mailto:gnewell at ameritech.net > > >_______________________________________________ >Pianotech list info: https://www.moypiano.com/resources/#archives Greg Newell Greg's piano Forté mailto:gnewell at ameritech.net
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