To turn a long piece of square wood into a shapely cylinder on the wood lathe, first your going to have to chop off the corners and turn it into an OCTAGON.
Now, I remember most of my high school trig and know a few ways of marking off corners and measuring to get that perfect octagon from a square, but oh the cosines and tangents and finding a pencil and ruler is such a bore!
Here's the absolute easiest way to do it on a table saw with an angle adjustment, like the one at San Jose Techshop.
Firstly, before you do anything, MAKE SURE THE SAW IS OFF! Unplug it, take out the key, do whatever you have to to ensure it cannot go off while you are laying things out.
Go ahead and tilt the saw to a 45 degree angle. All the way over!