After a failure another way, what I ended up with was a red oak disk about 12 inches in diameter to provide about a 6 inch radius. I glued up a blank, sawed it to a hexagonal shape, turned it round on my wood lathe. TThen I rough cut a groove with a gouge, followed by using a custom ground tool to finish turn a groove on the circumference to match my 7/8" 1/16" wall 304 SS tubing. I bolted this to my workbench. I screwed down a straight piece of wood 2 or 3 feet long to lead up to the disk to hold the trapped end.
I then loaded a piece of material and tried it ... just moved the workbench. Then I braced the workbench diagonally from a wall at the floor up to the top edge of the bench in line with the disk. Now I got somewhere. I managed a reasonable looking bend with a surprising amount of force needed.
Start with a piece that you figure is about 3 inches long, just to be sure. You need to carefully mark your starting position and observe what you get after performing the initial bend. The initial bend resulted in my piece growing about 1.5 inches in width, that is if I marked out for a 72 inch wide arch, I would actually get a finished width of about 75 inches. So knowing this after my first bend, I spaced my second mark at 69 inches to get a 72 inch finished arch width.
I have bent two arches for a bimini
, and four arches (two bent at about a 45 degree angle) for a solar
panel arch for my Tanzer 22. Each "45 degree" arches is welded below the 90 degree arch to form a truss like structure with some 3x3" 1/8" plate forming the webbing. I am happy with the bends, less so with the shaping and fitting of some of the pieces on the solar
panel arch that were welded in place. It will work fine, but the joints are ugly.
If anyone requests, I can post photographs of the bending setup and the bimini frame and solar panel arch.