Sharpening an ax is not difficult, but it does require a basic understanding of how the business end of an ax works. An ax is almost never used to cut perpendicularly through wood fibers; instead, the tool is used to slice into wood at an angle. When an ax strikes a log, the ax head needs to do two things: cut the wood fibers, and eject the chips it creates.
A properly sharpened ax takes both actions into account. To cut the wood fibers, the leading edge of the ax must be sharp. To pop the chips out, the part of the blade just behind the leading edge must have a wedge shape. An ax with too sharp an edge and not enough bevel will cut too deeply and be difficult to remove. An ax with sufficient bevel but not enough edge will be too blunt to bite and will simply glance off the log.
The way to determine the bevel on an ax is to look straight down the bit from the top of the head. The profile should look like a bulging V whose sharp point tapers so that the sides become more parallel.
An ax with a good bevel should only need to be touched up from time to time, but an ax with a poor bevel will require some time and elbow grease to restore. High-speed grinders should be avoided religiously for bringing dull axes back, as the heat they generate will change the temper of the harder steel found in the ax’s bit. A mill bastard file is a far better tool to use.
Start the process of sharpening your ax by clamping the ax head down on a flat surface. Then, while wearing gloves, run the file into the cutting edge at the desired edge bevel angle – 15 degrees is a good goal. Since you’re running your hands toward the sharp edge of the ax, it’s a good idea to make a guard by sliding a piece of leather or stiff cardboard onto the tang of the file; this will protect your fingers.
Proper sharpening strokes will take some practice, and it is important, as with most filing, that your stroke be smooth, steady, and, most critically, straight. Each fan-shaped stroke should start at one of the bit corners and end at the center of the bit. Keep count of your strokes, and after ten or so, do ten strokes from the other corner toward the center. Unclamp the head and examine the bevel profile. The filed side will be shiny, and you’ll see a slight burr pushed over to the unfiled side. Then turn the bit over and do the same number of strokes on the other side at the same angle and in the same manner. Unclamp the ax head and, looking down the bit from the top, examine the bevel profile. Are you getting the angle right? Are you filing evenly on both sides? To assist in these determinations, you can make yourself a filing template out of a piece of wood or cardboard. Use the illustration provided here to get started. Fit the template over your bevel to check your work.
Once the filing is done, hone and polish the bit with a whetstone. Start at the edge and rub the stone along the edge in a circular motion, then turn the ax over and do the other side. Be sure you use either oil or water with your stone to float away the metal particles (generally oil for man-made carborundum type stones and water for natural stones).
When you’ve done both sides, place your fingernail against the edge. The edge should be sharp enough to bite into your fingernail.
Carl Demrow is a trail consultant and carpenter when he’s not busy tending his woodlot in Washington, Vermont.