Axe Restoration Project: Part 5, Sharpening
The next step is sharpening our newly refurbished bit. Fig. a shows the tools we’ll be using. Clockwise from the upper left we have a small glass of water for cleaning our stone and files, a leather glove for safety, a diamond file, a diamond stone, and our axe head. First, a word about safety. Unlike knife sharpening, in which case you have a stationary sharpening implement, and hold the blade in your hands, sharpening an axe will most likely involve keeping the bit stationary, and holding the sharpening implement in your hand. This means that the blade and your hands are not moving in unison, making it much much easier to cut yourself. It is for this reason that we highly recommend wearing leather gloves while sharpening. They’ve saved our knuckles more than once.
There are many ways to sharpen every blade, and we are always exploring different methods and techniques. If you have tips or suggestions we welcome them in the comments section.
The first step involved with our bit is to remove the pitting along the bit edge that we mentioned in our previous installment. This we accomplish by clamping the head to a sturdy work surface and then taking our coarse (325 mesh) diamond stone and moving it into and across the bit edge, utilizing the full length of the stone (fig. b). Placing a hand at either end of the stone gives more control and purchase on the stone. If a more aggressive tactic is needed you may want to use a bastard cut file first before moving on to the diamond stone. We don’t recommend the use of a bench grinder for two reasons, the first being that they heat up quickly and can damage temper, secondly they will give the bit edge a concave shape which would need to be removed anyway. Concave, or ‘honed’ edges are too brittle and prone to chipping for use on an axe.
With the course stone we remove the pitting in the bit and begin to give it a convex shape. This is where things get trickier and opinions vary. We prefer to give the final edge of the bit a flat bevel of 20º per side. This flat bevel will allow for more precise and consistent sharpening since it gives our diamond files something flat to lay against. Some people disagree, saying that a flat bevel will impede performance, making the bit stick in wood. While the last 16th of an inch of bit will be flat we eliminate the ‘shoulder,’ the edge that demarcates the final edge from the rest of the blade, that is typically found on knives. We make the transition from final edge to the axe cheek a smooth and rounded one, even though the last 16th of an inch is a flat bevel.
Once we’ve established the convex shape we want we progress through the higher grits of our diamond files. The folding file we show here is a DMT double sided Diafold. The red side has a fine mesh of 600, and the green side has an extra-fine mesh of 1200. As mentioned before, we use these files so they are flat up against the blade bevel, utilizing the full length of the file and pushing into and across the full width of the blade. All of our diamond sharpening tools we use with water. Dipping two fingers into a small glass and rubbing it across the diamond surface is usually sufficient. We never apply water to the bit edge for safety reasons.
Fig. c shows a close up of the bit edge. The thin light areas on the edge are called ‘candles’ and they indicate a microscopic flat area on the very tip of the edge. You may have to look at the bit edge at various angles in order to see any candling. These candles indicate dullness and should be eliminated with continued sharpening with a diamond file. Be patient and persistent in your sharpening, it can take a fair amount of time at each stage to achieve a great edge. Whatever you do, do not rush. Rushing only leads to poor workmanship and possible injury.
A well sharpened bit should be smooth enough to reflect light like chrome. If you wish you can finish the edge with a fine waterstone and/or strop it with a diamond paste. The bit we’ve shown here is sharpened to a 1200 mesh diamond file. We may do some more touch up work on it later, but it’s plenty sharp for us at this point. We find it’s easy to carry our folding file with us in the field and it will quickly restore a nice edge.
Sharpening takes practice. As we mentioned earlier, we are always trying to improve our techniques. If you’re new to sharpening the best advice we have is to take it slow, and really pay attention to how every stroke of the file and stone effects your edge. You’ll soon get the hang of it.