Even the best custom knife is soon worthless without the skill to maintain it and, especially, skill to keep it sharp all the time. This short article describes one technique for knife sharpening - one that can be performed without specialist tools. If you choose to take the time to learn this method the benefit is that you will be able to sharpen your knife almost anywhere, even with improvised equipment.
It should be pointed out that these instructions are for creating an edge for cutting wood (or softer materials) and do not work if you are going to hack animal bones with the blade, for example.
What I present in this article is my personal opinion - these techniques work for me. You will find a technique that works best for you through practice and experimentation.
Knives that I use for cutting wood have an edge angle of approximately 21-22.5 degrees. I use the same angle in my camping knife. Note: this angle is not suitable for cutting all materials, all blade materials, and/or uses.
I use a flat or concave sharpening in my knives (flat if I do it by hand, and concave if I use a slow-speed grinder for the coarse work), with just a subtle (almost invisible) micro bevel sharpening to improve sharpness and edge retention. If the blade has a very prominent double bevel sharpening, as most tactical knives and pocket knives do, I remove it with a slow speed grinder or a file.
I always sharpen without guides or devices to help me keep the angle. I recommend anyone seriously interested in learning how to sharpen to do the same.
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I start the sharpening process by cleaning the blade and evaluating the condition of the blades edge. It is important to learn how to do this properly, it will save you a lot of time in the long run. At first it is difficult to see very small details or angles (flat, convex, concave, rounded, multiple angles etc.), but with practice your eye will learn how to see flaws that are extremely minute.
1) If the blade still cuts, is undamaged, but feels like it has lost its best edge I use a leather strop, or a belt, or a piece of leather on some even surface to make the edge smooth and sharp again. I do this by placing the knife on its bevel on top of the leather (I prefer the smoother side) and strop both sides of the blade. Note: same amount of strokes per side. By ”stropping” I mean moving the blade - always spine first – back and forth, like barbers in old western movies. There is no need to use a lot of force and you can elevate the angle very slightly. Some people use a few drops of oil on the leather, or even honing compound rubbed into the leather. NOTE: if you use compound take care to keep the blade evenly on its bevel. Do not elevate the angle to speed up the process or you will end up with a rounded edge. If you want to increase edge retention you can do this every time you have used your knife.
"Työstösuunta" means direction of movement...roughly translated.
2) If the edge has become so dull that stropping against leather is not enough I start by grinding the blade with a coarse whetstone (let's call this stage 1). I typically use a Japanese grit 220 waterstone, because it removes material very fast. Place the knife flat on its bevel on top of the whetstone and start moving it back and forth. Note: remember to use the entire length of the whetstone! This way your stone will stay even.
Again, press firmly but not hard - and relax. Using too much force makes the process less accurate and you might end up with multiple uncontrolled angles. Some people grind the blade with circular movements, others by moving the blade back and forth (straight or cross – relative to the stone). I prefer back and forth movement (cross), because it produces a pattern that makes it easier for me to determine how the work is proceeding.
In these two images I am using a self made sharpening tool, not a Japanese waterstone. It has been made by gluing a piece of sandpaper on a piece of plywood.
-> I continue to grind the bevel (the same side) until a burr forms on the other side of the blade. When a burr has formed it is time to work the other side. Grinding the other side goes basically the same way as the first one, except that it is more difficult to determine how the work is advancing (because of the original burr). One good indication that you have reached your goal is when the burr you have created by grinding the first side starts to peel of in small segments. Since the burr is often very very small, this might be a bit hard to detect. -> I repeat the whole process (both sides) a few times, but each time work more gently and with less strokes – this is important! -> After I am pleased with the result and using the coarse stone no longer makes the edge any sharper I move to the actual sharpening with a Japanese combination waterstone (king 1000/6000 grit). I start with the coarser side and the process is exactly the same as in stage 1. After I am done repeating the process with both sides of the stone I finish the sharpening by making a tiny double bevel to the edge. I do this by placing the blade on the finer side of the combination stone, flat on its bevel, and rising the angle just a bit.
Then I pull the knife towards myself and brush the whole length of the edge against the stone gently. I work the other side similarly and repeat the process a couple of times. You have to be relaxed when you do this and not second guess about the angle. If you start hesitating you will most probably produce multiple angles, which is not desirable. After this I strop the blade, as explained above in part 1).
3) If the blade is very dull, has obvious multiple (uncontrolled) angles, has a broken tip or other damage I use a file or a slow rotating grinder or both to correct the situation and then move to part 2), with the exception that only very little work is required with the coarse stone, especially if slow speed grinder was used.
Testing sharpness:
Most people think that a blade that can shave hair is very sharp, but they do not know that almost any piece of scrap metal can be made “sharp” enough to do that. When I test a blade I usually inspect it visually first. I hold the blade in line with a bright light and see if any part of the edge has any glints. A glint means there is a dull spot or that there is a segment of burr still attached to the edge. You can remove the latter with a leather strop.
Another way to determine sharpness is to scrape your fingernail or hair in the back of your head with the blade and changing the angle. If the blade “bites” at approximately 35 degree angle or less and does not slide you can be pretty confident that it is sharp enough.
Splitting hairs test:
Take a hair from your head (or borrow one if you do not have any), make it loop between you fingers (a small one) and gently split the hair in two. When you can do this you can be pretty confident that you are doing something right – especially if the edge still retains sharpness well.
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