<!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 6.00.2900.3354" name=GENERATOR> <STYLE></STYLE> </HEAD> <BODY bgColor=#ffffff> <DIV><FONT face=Arial color=#800000>My ears started itching really bad. Sorry to be so illusive, duty calls, ya know...Anywho:</FONT></DIV> <DIV><FONT face=Arial color=#800000></FONT> </DIV> <DIV><FONT face=Arial color=#800000>I understand crowning more or less along the lines of David, I think. The stiffness comes predominantly from the rib design (namely the dimensions but also the MOE) and the crown is built in to exceed the predicted deflection by a given percentage. We're talking about RC&S here and hybrids to a certain degree. Crown and deflection give us an indicator to ultimately judge the amount of stiffness. Ron N has been collecting data on spring rate and would be a more reliable authority on this. In the traditional CC board, crown isn't as predictable and therefore is more of a result than a design feature; although we still measure it to get a sense of the stiffness via compression.</FONT></DIV> <DIV><FONT color=#800000></FONT> </DIV> <DIV><FONT face=Arial color=#800000>As for methods of cutting rib radii:</FONT></DIV> <DIV><FONT color=#800000></FONT> </DIV> <DIV><FONT face=Arial color=#800000>There's ye ol' router sled (see picture). You'll need one per radii. Michael Morvin makes the best templates (picture posted) for all your crowning jigs from rib presses to cauls to sled runners (picture posted) and I bought a few before I finessed my router base, based on the old sailor's trick that Andrew Anderson described or Ron N. You'll need to know the deflection for any given radii which is r-(r^2-(c^2)/4)^0.5 where r is the radius and c is the span. I readily admit that while this router base works outstanding, it was way more expensive to put together than buying Michael's templates.</FONT></DIV> <DIV><FONT color=#800000></FONT> </DIV> <DIV><FONT color=#800000><FONT face=Arial>I only have one "fixed sled" which I've used for the longest ribs on my more traditional projects based on a 50' radius (I thought this was quite aggressive when I was young<G>). This was supplemented by variable radii ribbing by an adjustable crowning sled (see pix). This sled works surpisingly well and I never went beyond the working model which I built eight years ago. It crowns ribs up to 90cm in length. The center of both runners are supported  by capstans, which refine the crown as well as support the weight of the router. I set the crown by turning the turnbuckle underneath, adjust the capstan in the middle and verify crown by sampling measurements </FONT> <FONT face=Arial>every inch on each side with a height gage. As far as thousands of an inch can measure, I'm producing arcs but even if they were catenaries or parabolas, it doesn't matter.</FONT></FONT></DIV> <DIV><FONT face=Arial color=#800000></FONT> </DIV> <DIV><FONT face=Arial color=#800000>My latest project was a M&H A designed by Ron N. Terry Farrell supplied me with laminated rib stock, which maybe someday he'll even invoice for (take your time Terry <G>). I'm absolutely a convert despite my earlier trepidation of rolling shear stresses. I just don't think the loads are great enough.</FONT></DIV> <DIV><FONT face=Arial color=#800000></FONT> </DIV> <DIV><FONT face=Arial color=#800000>I hope this helps, now back to my cave...</FONT></DIV> <DIV><FONT face=Arial color=#800000></FONT> </DIV> <DIV><FONT face=Arial color=#800000></FONT> </DIV> <DIV><FONT face=Arial color=#800000>Jude Reveley, RPT<BR>Absolute Piano Restoration, LLC<BR>Lowell, Massachusetts<BR>(978) 323-4545</FONT></DIV> <DIV><FONT face=Arial size=2></FONT> </DIV> <DIV><FONT face=Arial size=2></FONT> </DIV> <DIV>----- Original Message ----- <BR>From: "David Love" <<A href="mailto:davidlovepianos@comcast.net">davidlovepianos@comcast.net</A>><BR>To: "'Pianotech List'" <<A href="mailto:pianotech@ptg.org">pianotech@ptg.org</A>><BR>Sent: Thursday, August 07, 2008 10:22 PM<BR>Subject: RE: Cutting rib radii<BR><BR><BR>> Is it true that the tighter the radius the stiffer it is?  I don't think<BR>> that's true.  When I'm setting up rib deflection calculations I don't<BR>> concern myself with a change in stiffness that a tighter radius will<BR>bring,<BR>> rather it is the total amount of crown for a given length of rib and the<BR>> total amount of deflection that I consider.  A rib of given dimension will<BR>> deflect the same number of mm's for a given load, but the amount of<BR>> remaining crown will vary as a function of how much you had to begin with.<BR>> That's the reason you might consider adjusting the radius.<BR>><BR>> As far as how important the type of curve produced is, I defer to those<BR>who<BR>> have commented that it doesn't probably make much difference.  Also, in a<BR>> compression style board, I would imagine the curve formed by the rib being<BR>> bent by panel expansion is not a perfect circular arc.<BR>><BR>> David Love<BR>> <A href="mailto:davidlovepianos@comcast.net">davidlovepianos@comcast.net</A><BR>> <A href="http://www.davidlovepianos.com">www.davidlovepianos.com</A></DIV></BODY></HTML>