Thanks to everyone for your ideas on how to make the octagon cross-section from a 4" x 4" square.
I made it and it came out just great!
I finally did it on my jointer. I set the fence at 45 degrees, and it only took about 20 passes per corner to form the octagonal cross-section.
And, the best part was how SAFE it was!
One small problem I had was making sure I held the piece down on the outfeed side. A few passes I kept too much downward pressure on the infeed side and the material didn't come off equally. I just have to remember to push on the infeed side and apply downward pressure on the outfeed side.
Again, thanks to everyone.