We wanted to restore the sharp bevel on the cutting edge of my by-pass pruners. It is important to sharpen a bevel at the proper angle, the angle set when it was manufactured. To sharpen the bevel evenly, and to follow the proper angle, start by taking a magic marker and coloring the bevel on the cutting edge of the blade. If you are doing the job correctly, your file strokes should remove the magic marker coloring evenly across the full width of the bevel as you work on it. If only a small portion of the blade turns shiny, you need to change the angle of your file slightly.
What a great tip! I've sharpened my pruners before, and always find it tricky to get the angle just right. I never would have thought of using a marker as a guide, but I know greatness when I see it! Thanks, Henry!