Knifecraft (Part 2)
The best knife, with the greatest sheath isnít going to be worth a damn if you canít keep it in good working conditions. Sharpening is the most important aspect of knife maintenance. A dull knife makes mundane tasks hard and is dangerous to the user (more strength needs to be used, which increases the chances of injury). So weíll start there.
Field sharpening needs to be simple, quick and rely on equipment thatís light enough to carry at all times. Forget about all those nifty guided sharpening system and those sets of big beautiful Japanese water stones. We need something that will fit in a pocket, and if it has multiple uses all the better. Anything that requires oil is pretty much out, there are perfectly good options that work without any sort of lubricant.
This pretty much narrows the choices down to small diamond sharpeners and my personal favourite, humble sandpaper. Diamond sharpeners are great, you can get them in loads of different sizes and the good ones last forever. They can be very thin and easy to carry. They also cut through metal very fast. Iíve tried several brands, DMT and Lansky have both worked well for me. Try to get one of the credit card sized sharpeners or the double sided pocket ones (they have two different grits). My only beef with diamond sharpeners is that even the finest grits leave too much of a ďtoothyĒ edge for my taste, but I admit to having a bit of OCD when it comes to edge polish.
Why would I take sandpaper over diamond stones? Itís cheap, light and can be easily adapted to sharpen a variety of different tools and blade grinds. Depending on what you use to back it you can use sandpaper to sharpen convex blades on knives, axes and machetes much better than with any flat stone. Sandpaper also has multiple uses, a plus for any piece of bushcraft kit. Besides sharpening it can be used to finish carvings, to get a lot of very fine sawdust for fire starting (coarse grit sandpaper rubbed over fatwood makes pretty good tinder!), to clean rust off metal objects, etc.
Thereís nothing wrong with Arkansas stones, ceramic stones, etc. In fact, I prefer my Spyderco ceramic stones to any diamond stone. The problem is they take up a lot more room, are more fragile and weigh a lot more, making them a poor choice for a minimalistic field sharpening kit.
No matter whatís your sharpener of choice, you should add a strop. A simple piece of leather with some abrasive compound (metal polish, buffing compound, even toothpaste works). Strops are tremendously useful and they are usually all you need to keep a keen edge on your knife.
Blade steel will affect ease of sharpening, so you need to take that into account when deciding what sort of stone or sharpener to carry. I try to avoid steels with very high abrasion resistance, such as ZDP-189 or D2, because while they hold an edge superbly it takes a while to sharpen them with limited tools. Fixing a little chip or roll in the edge becomes a daunting chore. I prefer simple carbon steels like 1095, O1, 52100 which hold a nice fine edge pretty well but are easy to sharpen with very basic equipment.
Skill plays a huge part as well. Some guys can get a scary sharp edge on very hard abrasion resistant steels with ease. If youíre one of those fellows who have reached sharpening Nirvana, skip this article because thereís nothing for you here.
Alright, weíve got our knife and our sharpening tools; now letís take a look at how to use them. As I mentioned before, there are different grinds and sharpening each kind takes a slightly different technique.
In the amazing drawing below you can see the main knife grinds available (there are more):
1- Convex grind. The blade curves constantly from the spine to the edge. Thereís usually no edge micro-bevel. Itís very strong and the edge can be very thin without sacrificing much toughness. Itís excellent for outdoors work. It was Bill Moranís grind of choice; custom makers like Ed Fowler use it. Very few production companies use it, because it needs to be done by hand (Bark River and Fallkniven are the main ones, Marbleís still uses it but adds a micro-bevel). As you might have guessed, most convex knives are pricey.
2- Scandi grind. The correct terminology would be ďsabre grind with no secondary bevelĒ, but knife geeks the world over just call it a Scandi grind. Itís cheap to make, great for woodwork and ridiculously easy to sharpen to a scalpel edge, even by people with almost no sharpening experience. Itís probably the most popular bushcraft grind. Its main drawback is that the thin edge can be a bit weak, but there are ways around that (weíll get there, have some patience).
3- Full flat grind. This is the type of grind found on most Swiss army knives. If done properly, itís really efficient. It has a secondary edge bevel (sometimes called a micro-bevel), and itís not as easy to sharpen as a convex or Scandi grind. With time and after a lot of sharpening, the edge bevel gets broader and broader, so the ďshouldersĒ need to be ground down to keep cutting performance.
4- Hollow grind. The choice of terrorists, child molesters and hippies. You guessed it, I donít like it. At least not in a fixed blade thatís going to be used for bushcraft. I tolerate it in folding knives (the venerable Buck 110 is hollow ground), but it just doesnít suit my needs in a fixed blade bush knife. First of all, itís weak because of the lack of material behind the edge and manufacturers tend to try to fix this using broader edge angles, thus reducing cutting ability. This type of blade geometry also tends to bind in deep cuts, since it doesnít effectively push the material apart. Longevity isnít great either, as you wear the blade down thickness increases non linearly resulting in an obtuse edge geometry.
I donít want to get into detail, I could bore everybody here to death with pages and pages on the pros and cons of each type of grind but knife theory is not whatís important here.
Sharpening a convex knife is best accomplished using sandpaper backed by something with a little give, so that in can follow the natural curve of the blade. Some people use rubber, some use leather, some just lay the sandpaper over their leg. Place the blade on the sandpaper without pressing too hard (or youíll round the edge) and pull back making sure you drag the whole length of the edge through the paper. Thatís it. Finish the edge on the strop for a gleaming hair whittling result.
Youíll get scratches on the knife, but theyíll polish off as you move from coarser sandpaper to finer one. This sharpening method has two main advantages: you donít need to worry about edge angles and since your sanding most of the blade cutting performance wonít decrease with the years (youíre effectively thinning the whole blade, not just the edge).
Flat stones and diamond sharpeners can be used to touch up convex blades, but theyíll only sharpen the very edge. This looks tidier to some people, but makes less sense from a performance point of view (which is all we care about).
Scandi grinds are dead easy as well, easier than convex grinds for most people. Thatís why we chose a knife with this kind of geometry. Just lay the whole bevel flat on the stone (or whatever youíre using) and pull back. Again, no angles to worry about. Youíll get scratches on the bevels, nothing to worry about. Itís supposed to be like that.
A Scandi grind thatís sharpened to a very thin edge can be a bit weak for some tasks (for instance if youíre working with frozen wood). The easiest solution is to convex it a bit, just sharpen it like you would a convex blade. Youíll end up with a Scandi ground blade with a convex edge which you can turn back into a true Scandi whenever you feel like it.
Flat and hollow grinds with secondary edge bevels are a bit trickier to sharpen properly because you need to match your sharpening angle to that of the narrow edge bevel. Most people who complain about being unable to get an edge on their knives are usually missing the bevel. Thereís no easy fix for this, practice is the only solution.
In order to make sure youíre using the correct angle, paint the edge bevel with a marker. If after running it through the stone the marker is gone, youíre doing it right. If itís still there, youíre missing the bevel. Once you get the angle right, keeping it that way is the next big challenge. You can use a piece of stiff rubber hose to help you. Mark the angle on the hose and cut a slot into it. Use the hose to hold the blade at the correct angle. It will eventually be burned into your muscle memory.
The main steps involved in sharpening are the same no matter what type of blade geometry youíre dealing with.
1- Start with a coarse grit and work your way to the finest one youíve got. As a general rule of thumb, the finer the grit, the more strokes youíll need. For example, after swiping a blade four times through a piece of 600 grit sandpaper, youíll need to do twelve or so passes on 1000 grit paper. This depends on how polished or ďtoothyĒ you want your edge.
2- A thin burr or wire edge means youíre doing things right. If your knife isnít very dull the burr might be hard to spot, but itís there.
3- You need to remove the burr to get to the actual edge. A strop is great for this, much better than a hard surface.
Itís better to strop the knife often instead of letting it dull too much. A few seconds of stropping every now and then can save you a lot of sharpening time. If you guys have any questions regarding field sharpening, ask away.
Rust is the other big issue in knife maintenance. Something that, in my opinion, is often blown out of proportion. Machetes, made out of steels like 1055, are the most used tools in tropical rainforest and they seem to hold up just fine for years. As long as you dry your knife before putting it back in its sheath, youíll be fine. Some surface rust might show up here and there, but itís nothing to worry about. If it gets too bad just use some sandpaper to remove it.
I donít recommend painting or cold blueing your carbon steel knife, those things are toxic and you donít want them in contact with your food. Thereís a cheap and easy alternative that will afford your knife some rust protection: a forced patina. If youíve seen well used carbon steel knives, you probably noticed that the blades are black or gray, stained from contact with different acids. This is a sort of very thin layer of surface oxidation that helps keep rust away (like blueing on guns). Your knife will develop this patina over time, but you can also force it. Just leave the blade in vinegar for a little while, or cover it in mustard. 1095 steel used in Mora knives takes a nice deep patina very quickly.
If you decide to carry oil in the field, get some food grade mineral oil. Itís basically baby oil without the perfume and other crap, itís dirt cheap and available at drugstores.
Next up: Pimp your Mora. And weíll be done with knives, I promise.