<HTML> In a message dated 11/1/03 12:53:13 AM, RNossaman@cox.net writes: <BLOCKQUOTE CITE STYLE="BORDER-LEFT: #0000ff 2px solid; MARGIN-LEFT: 5px; = MARGIN-RIGHT: 0px; PADDING-LEFT: 5px" TYPE="CITE">No, it won't. It will= be curved more in the middle and less at the ends. I used two straight edges. Starting with a line representing the anticipated<B= R> maximum length of a rib of that particular radius, I computed the height of<= BR> the arc segment represented by that chord at that radius. Then I drove pins<= BR> in the points at the ends of the chord, and the center of the arc segment<BR= > at the computed height above the chord. Placing the two straight edges one<B= R> each on the pins at the ends of the chord, and overlapping above, but both<B= R> touching, the pin in the center, I tacked them together. Placing a pencil<BR= > in the shallow V produced at the intersection of the straightedges, I slid<B= R> the straightedge assembly on the three pins so that the pencil went from one end of the chord to the other - describing the arc segment. Realistically, the exact shape of the described arc isn't anything like critical to the ultimate performance of the assembly. The chosen radii and<B= R> rib dimensions, balanced against the anticipated bearing load and resulting<= BR> deflection are significantly more important. </BLOCKQUOTE> believe this two straightedges method is shown in fine woodworking magazine,= and the formula for rise of segment/arc of a circle is in machinery's handb= ook. I am not strong on math but I presumed I had solved correctly when I di= d Wolfenden's suggested radius and it came out exactly .625 or 5/8 inch. My = question is:  why express these rises of arc in such an arcane fashion= as radius of a HUGE circle? Is it because of the need to be uniform despite= the length of arc required ? Glenn C.</HTML>