In the old days, the file was an axe man's best friend. The job of repairing a chipped edge was a long one that required great patience for the result to be satisfactory. Many lacked this patience which is why we see so many old, chipped heads laying around in old wood sheds.
I was experimenting with my favourite axe and decided on changing the edge and bringing it down to an 18 - 19 degree chisel grind. At this point I will say that an engineer's protractor like the one pictured is a great idea for anyone wanting to modify axes. Without it you are guessing at best and may end up repeating mistakes that will cost you time and possibly money.
I was interested to see how it would go in the relatively soft conifers and birch trees here in Norway. The day I went out we had a cold snap and the temperature was -3 C when I started chopping wood and dropped to a further -10 C over night. I warmed the head however despite my best efforts, the edge chipped. The chips were not too bad, but I still wasn't pleased I had chipped my favourite axe.
When I returned home, I decided to make lemonade from lemons and put up a tutorial on how one can repair such mishaps.
The first step is to set up your grinding jig to an appropriate angle. I don't use anything fancy, just a belt grinder with a piece of angle clamped into place. My jig gave me 23 degrees which is a degree more than a racing axe. If you add the slight convexing during sharpening then this will end up at about 25 - 28 degrees at the very edge.
The next step is to carefully grind until the chips are gone. I do this by resting the poll on the angle and arcing the bit lightly over the grinding belt. The harder you push, the more it heats up so be careful not to overheat the metal. A file is safer but takes more time. I work both sides uniformly until the chips are gone and I am left with a wire edge.
In the above image you can still see the remnant of the worst chip. Towards the toe of the axe though you can see the formation of the wire edge. This is a good sign and means that I don't have to grind much more in that area. I try to preserve my axes and unecessary grinding shortens the bit and thus shortens the service life of the axe.
Now once you have ground the chips out, use the protractor to check the angle one final time. Mine looks ok.
Now you don't need many tools to fix an axe. I do most repairs with the belt grinder, vice grips, drill, clamps, buffing wheel, stripping wheel and diamond hone. I am also mindful of safety and include earplugs and safety glasses as standard equipment.
Now clamping the axe to a work bench, fasten the stripping wheel into the drill. Be mindful of the rotation of the drill and change it so that the wheel spins away from the edge rather than into it. This will avoid catching of the edge and the axe or drill being flung uncontrollably. Now make light passes so that the newly ground portion of the blade is blended into the old. Once this is done, you will only slightly notice the transition between the old and newly ground portions of the bit. Change the wheel to the buffing wheel and give it a final polish in the same manner.
Repeat the same procedure on the other side. You may notice the wire edge has disappeared in some areas. This is not a necessary part of the procedure as the final sharpen with the diamond stone / hone will take care of that. Take the axe and give it a final sharpen. Give each side light passes with the stone / hone and then slice some wood lightly with the edge. This will remove an remnant of the wire edge. Now youcan strop or use a ceramic hone on the edge. The final step is to work harden the edge. Find a solid piece of wood and give it some very light chops with the axe. I use about 10 chops, spacing them out along the length of the edge so every portion is hardened.
Now go and test the axe to make sure everything has come together. I do this by finding some seasoned wood or frozen wood. In this case it was some frozen beech. The axe threw lovely big chips.
This is the benefit to a properly profiled axe. Nice deep cuts and ejected wood. A close up of the cut and the final condition of the edge.
as you can see, no damage to the edge at all. The extra 5 degrees makes a HUGE difference in the edge strength and the final slight convexing of the edge helps a great deal too. My convexing is very slight and is only done to the first 1 - 1.5mm of the edge so is hard to see. I have my favourite axe back in fighting form.