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Old 08-20-2010, 04:55 AM   #121
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Knifecraft (Part 2)

The best knife, with the greatest sheath isn’t going to be worth a damn if you can’t 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 we’ll start there.

Field sharpening needs to be simple, quick and rely on equipment that’s 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. I’ve 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 “toothy” 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? It’s 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.

There’s 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 what’s 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 you’re one of those fellows who have reached sharpening Nirvana, skip this article because there’s nothing for you here.

Alright, we’ve got our knife and our sharpening tools; now let’s 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. There’s usually no edge micro-bevel. It’s very strong and the edge can be very thin without sacrificing much toughness. It’s excellent for outdoors work. It was Bill Moran’s 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, Marble’s 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 “sabre grind with no secondary bevel”, but knife geeks the world over just call it a Scandi grind. It’s cheap to make, great for woodwork and ridiculously easy to sharpen to a scalpel edge, even by people with almost no sharpening experience. It’s 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 (we’ll get there, have some patience).

3- Full flat grind. This is the type of grind found on most Swiss army knives. If done properly, it’s really efficient. It has a secondary edge bevel (sometimes called a micro-bevel), and it’s 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 “shoulders” need to be ground down to keep cutting performance.

4- Hollow grind. The choice of terrorists, child molesters and hippies. You guessed it, I don’t like it. At least not in a fixed blade that’s going to be used for bushcraft. I tolerate it in folding knives (the venerable Buck 110 is hollow ground), but it just doesn’t suit my needs in a fixed blade bush knife. First of all, it’s 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 doesn’t effectively push the material apart. Longevity isn’t great either, as you wear the blade down thickness increases non linearly resulting in an obtuse edge geometry.

I don’t 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 what’s 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 you’ll round the edge) and pull back making sure you drag the whole length of the edge through the paper. That’s it. Finish the edge on the strop for a gleaming hair whittling result.

You’ll get scratches on the knife, but they’ll polish off as you move from coarser sandpaper to finer one. This sharpening method has two main advantages: you don’t need to worry about edge angles and since your sanding most of the blade cutting performance won’t decrease with the years (you’re effectively thinning the whole blade, not just the edge).

Flat stones and diamond sharpeners can be used to touch up convex blades, but they’ll 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. That’s why we chose a knife with this kind of geometry. Just lay the whole bevel flat on the stone (or whatever you’re using) and pull back. Again, no angles to worry about. You’ll get scratches on the bevels, nothing to worry about. It’s supposed to be like that.

A Scandi grind that’s sharpened to a very thin edge can be a bit weak for some tasks (for instance if you’re working with frozen wood). The easiest solution is to convex it a bit, just sharpen it like you would a convex blade. You’ll 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. There’s no easy fix for this, practice is the only solution.

In order to make sure you’re using the correct angle, paint the edge bevel with a marker. If after running it through the stone the marker is gone, you’re doing it right. If it’s still there, you’re 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 you’re dealing with.

1- Start with a coarse grit and work your way to the finest one you’ve got. As a general rule of thumb, the finer the grit, the more strokes you’ll need. For example, after swiping a blade four times through a piece of 600 grit sandpaper, you’ll need to do twelve or so passes on 1000 grit paper. This depends on how polished or “toothy” you want your edge.

2- A thin burr or wire edge means you’re doing things right. If your knife isn’t very dull the burr might be hard to spot, but it’s 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.

It’s 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, you’ll be fine. Some surface rust might show up here and there, but it’s nothing to worry about. If it gets too bad just use some sandpaper to remove it.

I don’t recommend painting or cold blueing your carbon steel knife, those things are toxic and you don’t want them in contact with your food. There’s a cheap and easy alternative that will afford your knife some rust protection: a forced patina. If you’ve 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. It’s basically baby oil without the perfume and other crap, it’s dirt cheap and available at drugstores.

Next up: Pimp your Mora. And we’ll be done with knives, I promise.
grinds.jpg   sharpening.jpg  
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Old 08-20-2010, 05:03 AM   #122
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An example of patina on carbon steel. The top knife is a stainless Fallkniven F1, the one below is a Master Hunter (Cold Steel) made by Camillus in Carbon V. Although the picture is less than perfect, you can see the matt grey colour of the flat ground blade contrasting with the shiny edge bevel.

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Old 08-20-2010, 12:28 PM   #123
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Francisco-

You haven't by chance posted anything on YouTube demonstrating these sharpening techniques, have you?

This is fascinating stuff. I've been collecting knives for years and think I've learned more in the last week than in the past 25 years.

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Old 08-20-2010, 01:13 PM   #124
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Cisco

Just to be sure I have this right. When sharpening my new Mora I draw backwards on a fine stone. sandpaper, or leather. I was taught way back when to cut forward into the stone.

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Old 08-20-2010, 01:32 PM   #125
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Quote:
Originally Posted by ScottA View Post
Francisco-

You haven't by chance posted anything on YouTube demonstrating these sharpening techniques, have you?
Sorry, no video camera. These are just basic field sharpening techniques.

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Originally Posted by Jo da Plumbr View Post
Just to be sure I have this right. When sharpening my new Mora I draw backwards on a fine stone. sandpaper, or leather. I was taught way back when to cut forward into the stone.
Whatever works best for you. I'm only covering one way to do it to keep it short and simple. Moving forwards produces a finer burr than drawing backwards and is the prefered method for some knife guys. Other people move the blade in circles.

You've got to draw backwards when sharpening convex grinds or using the leather strop, or your edge will cut into the sharpening media.
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Old 08-20-2010, 01:45 PM   #126
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Sorry brother more dumb plumber questions.

When you sharpen with sandpaper do you lay the paper on a hard flat surface? Sort of creating your own whet stone?

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Old 08-20-2010, 02:11 PM   #127
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Originally Posted by Jo da Plumbr View Post
When you sharpen with sandpaper do you lay the paper on a hard flat surface? Sort of creating your own whet stone?
Sorry, I didn't make this clear enough. For flat and Scandi grinds I lay the sandpaper on something flat, it can also be wrapped around something like a pen and used as you would a honing steel.

For convex knives I place some rubber or leather (usually my strop) between the hard surface and the sandpaper to allow it to follow the curve of the blade. Sometimes I just use my thigh.
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Old 08-20-2010, 02:16 PM   #128
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Originally Posted by Franciscomv View Post
Sorry, I didn't make this clear enough. For flat and Scandi grinds I lay the sandpaper on something flat, it can also be wrapped around something like a pen and used as you would a honing steel.

For convex knives I place some rubber or leather (usually my strop) between the hard surface and the sandpaper to allow it to follow the curve of the blade. Sometimes I just use my thigh.
I have tons of respect for you, and you know your stuff, but I'm not running a cold sharp piece of steel up my thigh.
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Old 08-20-2010, 02:22 PM   #129
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I have tons of respect for you, and you know your stuff, but I'm not running a cold sharp piece of steel up my thigh.
Oh come on Benny... you got nothin to lose.
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Old 08-20-2010, 02:29 PM   #130
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Originally Posted by Jo da Plumbr View Post
I was taught way back when to cut forward into the stone.
Jo,
I was taught the same thing. I was told that dragging it backwards would "roll the edge". I'm sure this is why the Master Chief explained to use light pressure when sharpening. I've got a couple of descent stones and have never used sand paper before, but for this exercise I am going to get out of my comfort zone and do like the Master Chief says.
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