I mark the shaft at 3/8", then cut down the center to the mark with a fine-toothed hacksaw. Then I use a little round rasp or a tile-cutting blade to widen the slot, and finish it out with sandpaper. I trim the square ends of the shaft down with a knife and smooth and round them with sandpaper. Just be careful and keep your slot straight and centered or your arrow won't fly straight. With a little practice, only takes a couple minutes per arrow.