<HTML><BODY STYLE="font:10pt verdana; border:none;"><DIV> Hi Phil<= /DIV> <DIV> </DIV> <DIV>   Comments interspersed below</DI= V> <DIV> </DIV> <BLOCKQUOTE style="PADDING-RIGHT: 0px; PADDING-LEF= T: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0= px"> <DIV style="FONT: 10pt Arial">----- Original Message -----</DIV> <= DIV style="BACKGROUND: #e4e4e4; FONT: 10pt Arial; COLOR: black"><B>From= :</B> Phillip L Ford</DIV> <DIV style="FONT: 10pt Arial"><B>Sent:</B> W= ednesday, November 21, 2001 10:46 AM</DIV> <DIV style="FONT: 10pt Arial= "><B>To:</B> pianotech@ptg.org</DIV> <DIV style="FONT: 10pt Arial"><B>S= ubject:</B> Re: Hamlet Davis bridge agraffes/ Reverse crown Steck</DIV> <= DIV> </DIV> <P>Dale,<BR>The reverse crowned board with downward bear= ing<BR>is an interesting idea. If you installed the crowned<BR>board into= the piano without ending up with compression<BR>preload then the downbea= ring should preload the board<BR>in tension to approximately the same deg= ree as it would<BR>preload the board in compression in the more usual<BR>= arrangement.</P> <P>Phil. ------ I,m not sure about that.  Perh= aps the deflection would be the same say 3 or more millimeters under stri= ng presurre but here's a thought.  With an upward crowned board the = pressure of downbearing does stiffen it but to my mind doing so  com= presses the wood molecules into a smaller space thereby having a constric= ting effect.I.E compression cracks & ridges.   In= the reverse crown model just the opposite is true. The wood molecules ar= e being tesioned or pushed apart. Not just the panel but also the ribs. I= s not the net effect the same as creating a reverse coil spring.  Se= ems to me the first model is compressing a spring and the other one stret= ching a spring. Whatever it is there is something very different about th= is system.</P> <P>     As I see it the purpose of the= crowning<BR>and preload due to downbearing is to stiffen the soundboard<= BR>system without adding mass (as you could do say by<BR>thickening the b= oard or adding heavier ribs). </P> <P>Phil--true this is the theory = and in practice balancing the impedance characteristicsthis is what = rebuilders  do but that idea has its limits. Obviously  to= o much impedance at some point provides diminishing returns. Ho= w much mass and stiffness is is enough are questions I ponder freequently= .</P> <P>Where you<BR>need this is at the top end, hence the substantial<= BR>downbearing at the top end, with almost none at the bottom<BR>end of t= he scale. </P> <P>Phil---In a pre-stressed downbearing setup even th= e bottom of the scale has some fairly significant pressure,but you are co= rrect that proportionaly the trebles have a greater down bearing force</P= > <P>  It would seem to me that the stiffening<BR>due to crowni= ng or arching the board would be the same<BR>whether it were crowned up o= r down.  It also seems to me<BR>that it wouldn't matter whether the = stiffening from the<BR>downbearing preload were a tension or compression = preload.<BR>It also seems that you would get the added benefit that as<BR= >the board tended to take on any set from the preload with<BR>the reverse= crown arrangement the set would tend to give the<BR>board more crown rat= her than flatten it out as in the more<BR>usual arrangement. </P> <P= >Phil- Surely this is true when considering the wood expanding and d= rawing into further tension with humidity However I'm not sure this desig= n would require as much panel drying before rib glue up(6% E.M.C.or so)&n= bsp;so compression set may not be as much of the equation. Although = I believe it would still require this reasonable amount so that it w= ould resist cracking over time because of its tension loading. When = I set up the bearing on a 6 ft. Julius bower with reverse crowning I= did not push it as hard as I would a positive crowned board as It sang l= ike an angel with modest downbearing before it was torn down for stringin= g and bridge caps etc. I didn't see any signs of compression set.</P= > <P> What would concern me is that wood tends<BR>to have much less = tension strength than compression strength<BR>across the grain and would = therefore crack or take on<BR>permanent set more readily with a tension p= reload than<BR>with a compression<BR>preload.  However, wood has muc= h more tension strength than<BR>compression strength along the grain and = perhaps this would<BR>help.  It's interesting that on the reverse cr= owned boards<BR>you have seen you haven't noticed deterioration due to th= e<BR>tension preload.</P> <P>Phil- It is very interesting indeed. The str= ength along the grain as you say must be a factor. One would expect = a great deal of cracking but the Bower had only a couple very small = hairlines right at the bridge end (note 27) which were easily hand shimme= d for cosmetics. Really this board looked like a salad bowl. My last comm= ent is that this design is intriguing because the sustain indicates quite= excellant power with and incredibly long ,free and unrestricted sounding= sustain thru out the scale. Considering recent discussions it's interest= ing  that the top trebles had hard and quite pointy triangular beari= ng bars for front terminations. They were held in  place by string p= ressure. Oh yeah longish backscales too. As I stated before I've encounte= red this design now by a variety of makers and each exhibited a sustain/f= ree sound that imediately grabbed my attention and the boards were not sp= lit up. Veeery interesting eehh. or at least much food for thought.</P> <= P>May you all have a wonderful thanksgiving. We are richly blessed!<BR>--= -<BR>   Best----- Dale Erwin</P> <P><BR><BR>On Sun, 18 Nov 2001= 06:48:16<BR>DALE ERWIN wrote:<BR>>Tom and list<BR>><BR>> &= nbsp;  You know I have been following this thread and it is interest= ing to me how many makers tried out this idea. I rebuilt a George Steck 6= ft. grand last year with this arrangement. When I first encountered the = piano the sound was absolutely magic. The sustain just floated for what s= eemed like forever . The more interesting thing was that the board was a = reverse crowned board with a positive set downbearing. I mean bearing set= pressing in the usual direction.<BR>>   A bit more time con= suming to string but what a gem. I keep finding all kinds of sound board = conditions and configurations which aren't supposed to work that do and o= thers that should that don't!<BR>>  I have to figure that the wei= ght of the Big  Brass agraffes also contributed to the impedance pro= perties of the board probably a sustain enhancing dynamic.<BR>><BR>&gt= ;       Ain't life interestin---Dale Erwin-= ---- -----<BR><BR><BR><BR></P></BLOCKQUOTE></BODY></HTML>