>Ron, > >My understanding, from a class with Clair Davies at the PA convention a >few years ago, was that the beauty of 2 x 6 yellow pine was its >particular abilty to bend just enough from the pressure of the pneumatic >hoses to give the crown desired. Therefore using yellow pine is critical >to his design. Clair was always making improvements, however. You may >know more about this than I do. > >Roger Hayden, RPT Beauty is, indeed, in the eye of the beholder. I considered the spring factor, but rejected it. I was just as happy to make the cauls more rigid with maple, cut the radius that appropriately matches the rib into each caul, and depending on these factors to define the crown under pneumatic load. It may not really make a heck of a lot of difference at the end, but I like the illusion of having some control of the process, and since I use different crown radii in different areas of the board, all of them smaller than 60' (no, sorry, can't say), this seemed more predictable and controllable. I've always been leery of "automatic" results achieved by the expected average response of any system under generally defined conditions. I've had to eat the results too many times in my own past experiments, and in the use of products produced by others, so I tend to over-build and design in closer control than I might realistically need (or ultimately get). Call it a personality flaw, if you will. I prefer to see it as building in a bigger safety margin, even though it may very well *be* a personality flaw. I also only made five clamps, one of each radius, appropriately long. This kept the total cost at only slightly over $100, and I have already established to my satisfaction that I don't have to clamp all the ribs down at once, but can keep the panel at 6%EMC long enough to leapfrog the clamps every hour or so and spend maybe half a day gluing on a set of ribs. I machine crown the ribs, so the panel EMC isn't nearly as low, or as critical, as what (I think) Claire is doing. I can't find my Journal with the belly man survey, but I think I remember that he's using flat ribs and relying on panel expansion and caul deflection to form crown. With a spruce to spruce joint using Titebond, anything over about fifteen minutes is gravy for clamp time because the death grip has already been activated by then and you couldn't pry the pieces apart without destroying them whatever you tried. Harder woods need longer clamp time. In any case, I can find space on the ceiling to store five clamps, where 18 or 20 would be a stretch. For what it's worth, that's why I did it this way. Ron N
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