If it's a hardwood and you have a power drill, leave the ends long, chuck on a finishing nail driven into the long end and have a friend spin it in a plastic v-notched guide while you hold a sanding block to chamfer.

For your assembly guide, if pieces are straight and round you only need a piece of angle iron or similar long V-section thing and it will align perfectly. Use a small compass or miter square to find center and punch it before pilot drilling a 1/8" hole through a guide block set perpendicular.