-Kim Taylor, Guelph Canada 1998
You'll need (ideally) a bandsaw, a tablesaw, a spokeshave and a plane.
By the way, this took me a lot of years to figure out, so anyone who thinks they may make a bo for themselves one day, pay attention and save yourself a lot of work and thought.
On the tablesaw, cut the wood square to the maximum width you want, usually 1" or sometimes 1 1/8". I'll assume you want to make a bo of 1" in the centre dropping to 3/4" at the tip.
To taper the wood, mark the piece from the maximum width in the centre (or 6" from the centre or whatever you prefer) to 1/8" in from each side. Draw lines and then plane this taper into the four sides, make the lines as straight as you can get them. That's 8 surfaces to plane in all.
Now carefully mark out lines on opposite sides. In the centre make a mark 4.8 16ths of an inch in on each side. (0.3 of an inch).
On the ends make a mark 3.6 16ths of an inch in from each side (0.3 times 3/4"), and make a line between these marks.
Now set the bandsaw to make a 45 degree cut and cut along the lines. This will give you an octagonal shape with pretty much equal sized planes. Now go to work with the spokeshave and round the edges off the octagon as smoothly as possible.
Then go at it with sandpaper and finish the job.
If you don't have the tablesaw and bandsaw, try and get a piece of the right square size from a local lumberyard, mark the 0.3 lines on all four sides rather than just two, then use the plane to cut the four sided piece into 8 sides before switching to the spokeshave (it's hard to cut a straight plane with a spokeshave unless you have a lot of practice).
Have fun!