Lay it in a "V" groove and push the end up against some sandpaper at a perfect 90 degrees and twist the arrow. I made a jig for this.....one 3 x 8 x 3/4" piece of pine with a saw-curf cut lengthwise down the 3" side. Then a attatched a piece of 1/4" plywood perfectly square to the end. Oh, you'll need to remove some material off of the pine at the end were you attach the plywood so there is a place for dust and debris to fall to. Otherwise it'll clog up and will no longer give you a true edge. I've used this jig for a few years thinking about marketing it....then I see G5 has a product out called the ASD - Arrow Squaring Device - it's the same dang thing.