Logs will split radially right down the grain, usually. When you get osage orange or locust down to one ring you can see longituninal grain lines on the back. They aren't long and you need the light to be slanting to see them well. I figure out approximately where I want the center of the stave to be. Then I trace down those thin little lines toward one end of the stave with a thin marker, jumping stright from the end of one to the next one. When you are done tracing your line all the little grain lines alongside your "middle line" should be parallel to it. Do the same down the other limb. That's your centerline. If not suitable, because your stave is too narrow on one side, just make another line parallel to the forst and offset.
Of course once you have the centerline you lay out the bow by setting lines off deom the midline.
