<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML><HEAD> <META http-equiv=Content-Type content="text/html; charset=ISO-8859-1"> <META content="MSHTML 6.00.2900.2802" name=GENERATOR></HEAD> <BODY id=role_body style="FONT-SIZE: 10pt; COLOR: #000000; FONT-FAMILY: = Arial" bottomMargin=7 leftMargin=7 topMargin=7 rightMargin=7> <DIV> <DIV>In a message dated 2/19/2006 3:15:56 P.M. Pacific Standard Time, sec@overspianos.com.au writes:</DIV> <BLOCKQUOTE style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: blue 2px solid"><= FONT style="BACKGROUND-COLOR: transparent" face=Arial color=#000000 size=2>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 foll= ows that there would be no downbearing force. The SIN of zero is zero so t= he string tension vector component force would be zero. If the dow= n bearing angle was 90 degrees, with the speaking length segment paralle= l to the board and the back scale heading vertically downwards, the dow= n 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 16= 0 lbs unison string tension with a downbearing angle of 2 degrees, the downbearing vector force for this unison string would be; &nbsp= ;   Downbearing = 160*Sin2.0     Downbearing =5.58= 3 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 downbearin= g. If you measure a few pianos around the place you'll find that ther= e 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 pia= no. Bösendorfer have typically set their pianos with angles approach= ing 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 n= o. 5 with a Lowel gauge and it measured almost right on 1.3 degrees over th= e 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 giv= en piano, I suggest that you set up a spreadsheet to calculate the downbearing force you are planning to set up per rib. Note also th= at setting an unstrung angle of say 1.5 degrees won't result in a downbea= ring force of tension X SIN(1.5). Its the resultant string deflection a= ngle when the piano is at pitch and the board has stabilised (sunken to equilibrium) under load which will determine the actual downbearin= g 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 measur= e a down bearing figure which on the face of it looks OK, but very often t= he sound board has sunken to a state where it is pushed almost comple= tely 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 be= ing applied or the unstrung angle wasn't set properly. Either the downbear= ing 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 fi= ne 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 downbeari= ng gauge might indicate. Get an accurate downbearing gauge and a thread length for looking at crown, and measure a few pianos old a= nd new. You'll develop a picture of what's happening. Ron O</BLOCKQUOTE></DIV> <DIV></DIV> <DIV> </DIV></BODY></HTML>