And now a second stroke of woodworking luck: at a boatyard on the eastern shore of Maryland I found 6’ of 12-inch-wide, 4/4 (i.e., 1 inch plus) rough-hewed African mahogany for $10 and another piece of finished Afr mahog – 24”x 6” x 1” for about the same price (go figure!). I immediately bought them and drove home scheming on how to use them. I took the longer plank and cut six disks of 11” diameter. I then took two of these disks and cut out an interior circle of 7 ¼” dia. (that’s the width of the tube from one flat side to the other; from corner to opposing corner, the width is 7 7/8” (see calculator above)). Then I traced the dimensions of the external octagon onto the ring and cut the corners out with a handsaw. Long story, short: African Mahogany is useful to boat builders because it is rot resistant, but it is not the hardest hardwood out there, and is in fact somewhat brittle. The first ring snapped as I was sliding down the tube, the other snapped several times as I was cutting out the corners. I glued the rings back together a couple times. Broke them again. And started thinking about plan B.