Cutting Edge Information

Today Boys and Girls, we have input on one of the basic standard implements of our world- the knife. Learning wisely about this item will be useful no matter what you do, from your kitchen to your toybag.

"It never hurts to ask unless you're talking to a dominatrix."Mark Morford

Introduction

“Knife sharpening is hard.”
“Sharpening is too difficult and time consuming to do at home.”
“Send your knives to a professional sharpener once a year and you will be fine.”
“You have to spend hours hunched over a heavy hone slathered with oil.”

This well-intentioned advice is parroted in cooking schools, Food Network television programs, professional manuals and cookbooks. And it is just plain wrong.

Okay, maybe not so much wrong as misleading.

Knife sharpening is not difficult. It is not shrouded in mystery. With a little knowledge, a little geometry, a couple of tricks and some inexpensive tools, knife sharpening can be fairly easy and extremely rewarding. At the very least it’s a great skill for the toolbox. You’ll come away from this clinic with a better understanding of edges, steel and how to maintain your knives yourself. Or, if you decide to send them out, you’ll know how to make sure you’re getting what you want – and what you pay for.


Section One: The Sad Truth About Kitchen Knives

To a chef, there is nothing more important than his knife. It is not only an extension of his hands, it is an extension of his very personality. The knife is a chef’s paintbrush.

So why are most kitchen knives so bad?

The knives found in most commercial and home kitchens are designed for the lowest common denominator. The manufacturers of these knives make a series of compromises calculated to keep the largest number of people happily using their knives for the longest period of time. Like supermarket tomatoes bred for sturdiness and uniformity rather than flavor, these compromises seriously degrade the performance of your knives.

The first compromise begins with the steel. Steel is the heart of the knife. Most manufacturers (Henckels, Wusthof, Forschner, et al.) have proprietary steel blends and are very close-mouthed about the actual formulation of their steels. According to industry insiders, these steel blends are closely related to or equivalent to a steel known as 440a. By and large 440a steel is formulated for stain and wear resistance rather than holding a high performance edge.

In the kitchen, that’s not a bad tradeoff.

But this compromise in edge performance is compounded by a heat treatment that leaves the steel much softer than it could be. In general, the harder the steel, the keener the edge it will take. However, a hard steel makes it more difficult to get that edge in the first place. So manufacturers leave the steel a little soft, theoretically making sharpening at home easier. If you’ve ever spent an hour or two trying to get a super fine edge on a cheap kitchen knife, you’ll know that there is a big gap between theory and practice.

Upper-end kitchen knives like Henckels, Sabatier, Wusthof, et al., are a little better, but are still softer than they need to be at 52 to 56 on the Rockwell C scale (the Rockwell scale is a scale used to measure the relative hardness of different solids). By contrast, Japanese knives tend to be around 61-62 on the Rockwell scale. Custom knife maker Phil Wilson hardens his S90V (a stainless supersteel) chef’s and filet knives to 62-63 Rockwell.

The next compromise is in the factory edge angles. Most kitchen knives come with an edge that is at least 25 degrees per side, frequently even greater. If you add the two sides together you get a 50 degree included angle. And that’s the best case scenario. Take a look at a protractor if you happen to have one lying around. Fifty degrees is extremely thick. An angle that obtuse is more appropriate for an axe than a chef’s knife. Again, the theory is that the thick angles will allow the edge to resist damage from impaction, rolling and wear better than a thin edge. But, as the song says, it ain’t necessarily so.


Finally, there is just plain cruelty and misuse. While I’m certain none of you would ever use the sharpener on the back of an electric can opener, or use a glass cutting board, or store your knives loose in a drawer or put them in the dishwasher, it does happen. And when you add soft steel and thick angles to the general abuse that knives see in the kitchen, you end up with tools that are more adapted for bludgeoning oxen than fine dicing a soft tomato.

Take heart. The news isn’t all bad. We can fix these problems. Geometry is far more important than steel. With some basic knowledge and the willingness to invest a little time, you can realistically expect a dramatic increase in knife performance.

First, do no harm: General knife care

- Use wooden or composite plastic cutting boards only. Glass, ceramic, marble and steel will cause the edge to roll or chip. Bad. Don’t do it.

- Don’t drop your knives in the sink. Not only is it a hazard to the person washing dishes, but you can also blunt the tip or edge.

- Don’t put your knives in the dishwasher. The heat may damage wooden handles and the edges may bang against other cutlery or plates.

- Keep your knives clean and dry. Sanitize if necessary.

- Do not store your knives loose in a drawer. Use a block, magnetic strip, slotted hanger or edge guards. The magnetic strip is not recommended if you have children or inquisitive pets.

- Finally, your knife is not a can opener, a screwdriver, a pry bar, box cutter or hammer. There’s a special place in Hell reserved for people who abuse their knives this way.

Second: Modify for performance

This is the easy part. Establishing and maintaining high performance edges is what this tutorial is all about. It can be as simple as steeling with the proper technique or as complex as creating specific edge bevel and edge aggression strategies for each knife in your collection. It’s all up to you.

While you can’t change the steel your knife is made from, you can certainly keep your knives at peak performance – and without too much difficulty. We’ll discuss high performance edges and sharpening strategies a little later in the tutorial.

Third: Modify for comfort

This is something very few chefs (and even relatively few knife makers) take into consideration. Ask any chef to show you his knife-hand calluses. He’ll have a thick one at the base of his first finger from the “pinch grip” used in most kitchens. He or she may also have another on the side of the second finger where the finger rubs against the bolster or dropped portion of the blade that extends below the handle.

He will also have aching hands and possible repetitive stress injuries.

In the interest of economy, most knife manufacturers leave the spines of their knives squared off. The edges of the spine can sometimes be sharper than the knife itself. That edge cutting into your finger can lead to blisters, calluses, reduced circulation, numbness and injury.

If you ever handle a chef’s knife made by Canadian knife maker George Tichbourne you’ll know that it doesn’t have to be that way. Tichbourne worked with several professional chefs when designing his kitchen knife series. One of the key features is a smoothly rounded spine. It doesn’t abrade your finger, cut off the circulation, make your hands numb or create any of the other discomforts associated with standard kitchen knives.

You can do the same in less than half an hour. Lock your knife, edge down, into a padded vise. The padding doesn’t have to be anything elaborate. Two pieces of flat rubber or leather will keep the jaws from scratching the blade. You’ll need a sheet of fine (600 grit) wet/dry sandpaper available at any auto supply store or an abrasive cloth, sometimes called a crocus cloth. Using a gentle shoeshine motion, lightly round the edges of the spine. You don’t have to buff hard or remove a lot of metal. All you need to do is break the sharp edge at the base of the spine. How far you take it is up to you. This simple modification will make a world of difference in the comfort of your knives.


Section Two: Steel

An Overview of Steel

By definition, steel is a combination of iron and less than 2 percent carbon. For centuries, carbon was the only alloying element. The problem in the early days of steel making was getting rid of unwanted elements, not adding new ones. However, there are a variety of alloying elements that are added to modern steels to impart various characteristics.

Iron alone is relatively soft. It does not hold an edge well, wears quickly and has little resistance to bending. Add a little bit of carbon and the story changes dramatically. The carbon combines with the iron to form hard carbide platelets cemented together in a matrix of iron. The combination is resistant to wear and bending and will take a keen edge.

Smaller carbides and a tighter grain structure allow for a stronger, sharper edge. Other carbide formers, like vanadium, can refine the grain of the steel further. Knives with a high vanadium content can take a very keen edge, but are harder to sharpen.

Carbon - Present in all steels, it is the most vital hardening element. Greater than 0.5 percent carbon content qualifies a steel as a “high carbon” steel.

Chromium - Added for wear resistance and corrosion resistance. A steel with at least 13 percent chromium is considered “stainless.” Chromium is a carbide former, so it also increases wear resistance.

Manganese - A carbide former. Manganese aids grain structure, increases hardenability, and wear resistance. Manganese is present in most cutlery steels.

Molybdenum - Another carbide former. Increases hardness, prevents brittleness, makes the steel easier to machine.

Nickel - Adds toughness and possibly aids in corrosion resistance.

Phosphorus - Essentially a contaminant.

Silicon - Increases hardness and strength.

Sulfur - Increases machinability but decreases toughness.

Tungsten - Increases heat, wear and shock resistance. Tungsten is the strongest carbide former behind vanadium.

Vanadium - Another carbide former. Contributes to wear resistance and hardenability. Vanadium refines the grain of the steel, which contributes to toughness and allows the blade to take a very sharp edge.

Most kitchen knives fall into the category of “high carbon stainless.” These knives generally contain between 0.5 and 0.8 percent carbon, 13 to 18 percent chromium and a little manganese, molybdenum, silicon, phosphorus and sulphur. This makes for a steel that is easy to produce, is very stain resistant and reasonably wear resistant. Knives from Global and Mac’s Superior line have some vanadium added for improved wear resistance and a finer grain, which allows the knife to be sharpened to an incredible edge.

Carbon Steel versus Stainless Steel

The great debate rages on. Carbon steel advocates claim that their knives take a keener edge, hold it longer and are easier to resharpen than stainless steel knives. Stainless steel users claim that carbon steel knives are unsanitary, leave an off taste in foods and that stainless knives hold an edge longer than their carbon counterparts.

Who’s right? Depends on your definitions and your environment. It’s not as simple as carbon versus stainless.

Carbon steels range from simple iron/carbon combinations to high-alloy tool steels that will cut through concrete without losing their edge. Stainless steels vary from very soft, extremely stain resistant dive knives to super stainless alloys, like Crucible Particle Metals’ S30V, a steel purpose-designed for the custom cutlery industry.

In the far less demanding realm of the kitchen, however, the carbon steel devotees are right. At least until they actually have to use their knives. Then it’s a different story.

Carbon steel kitchen knives generally are a little harder and stronger than stainless steel kitchen knives. They are easy to sharpen and take a screaming edge. And while the patina that develops on a carbon knife can be unsightly (unless you like that sort of thing), it isn’t unsanitary.

But in the wet, acidic environment of the kitchen, stainless rules. For all their faults, compromises and shortcomings, stainless steel kitchen knives work better and will hold their edges longer than carbon steel knives.

Doesn’t make sense, does it?

The culprit is corrosion – the effect of acid and micro-rusting. Even on what appears to be a mirror-bright, razor sharp edge, microscopic particles of rust and corrosion will form, attacking the edge and reducing its performance. Unless carbon steel knives are rinsed and dried frequently, their edges will degrade rapidly in kitchen use. The stainless edge will easily outlast them.

According to chef and knife maker Thomas Haslinger, “Acids of fruit and vegetables are fairly aggressive and will dull a carbon blade more quickly than stainless. The acid actually eats the edge.”


Section Three: Edge Basics

Most kitchen knives are flat ground, meaning that the blade tapers directly from the spine to the edge. Hollow ground, convex ground and saber ground blades are rarely found in the kitchen. I mention them only to confuse you.

Edges come in a variety of flavors. The most common are the V-edge, double beveled edge, chisel ground edge and the convex edge.
V-edges and double beveled edges are variations on a theme. The edge found on your kitchen knives is most likely a V-edge, meaning, oddly enough, that the edge bevels form a V, two surfaces intersecting at a line of (ideally) zero width.

A double bevel takes this idea a little further by adding a second, more acute, angle behind the edge bevel. This secondary bevel is sometimes called a back bevel or relief angle. It’s purpose is to thin the metal behind the edge. The thinner the edge, the greater the cutting ability. However, an edge that is too thin is susceptible to damage. So you add a smaller, more obtuse primary bevel to the very edge to give it the strength to avoid damage from impaction, chipping or rolling.

Chisel ground edges are primarily found on Japanese knives, especially sushi knives. The edge is ground only on one side. The other is side is flat. Hence they come in right and left handed versions. Chisel ground edges can be extremely thin and sharp. If the edge bevel is ground at 25 degrees and the other side is 0 degrees, you have an included angle of 25 degrees – considerably more acute than the average Western knife.

Sometimes known as hamaguri-ba, the convex edge arcs in a rounded curve down to the edge. Thus the final edge is the intersection of two arcs, creating a very sharp edge with more metal behind it than the standard V-edge. Convex edges are generally formed on a slack belt grinder, so they are difficult for the home sharpener to achieve. This can be remedied with the mousepad trick found later in the tutorial. See the Convex Grind FAQ for sharpening methods and a comparison of the convex edge with other edge types.


The back bevel also solves one of the great problems with V-edges, the fact that the metal behind the edge gets progressively thicker as the knife is sharpened over time. The knife doesn’t cut as well and becomes harder and harder to sharpen. The answer is to grind the shoulders off the edge at an acute angle, i.e. add a back bevel, then reestablish the primary bevel.

Micro-serrations: True or False?

Knife geeks frequently talk about “micro-serrations,” microscopic teeth on the edge of the knife. Is this really true? In a word, yes. Sharpening by its very nature creates a scratch pattern on the edge of the knife. The coarser the stone, the coarser and deeper the scratch pattern will be and the larger the micro-serrations. Conversely, the finer the stone, the finer and more polished the edge will be with less prominent micro-serrations. The real question is, which one is better?

This is one of the great debates in the knife world – the razor sharp polished edge versus a toothier edge.

John Juranitch in his book “The Razor Edge Book of Sharpening” is emphatic that a polished edge is the answer, that micro-serrations are indicative of a dull knife. His experience comes from sharpening knives for the meat processing industry. Meat cutters go through knives faster than tissues in flu season, so Juranitch’s conclusions are hard to dispute.

However, Joe Talmadge, author of the Bladeforums “Sharpening FAQ;” Cliff Stamp, physicist and knife nut; Leonard Lee, president of Lee Valley Tools and author of “The Complete Guide to Sharpening;” and many others have come to the opposite conclusion: that micro-serrations, in the right context, can be a very good thing.

What is the right context? Later on we’ll examine the difference between push cutting and slicing, their applications in the kitchen and the value of various levels of polish on your knife edges. Which leads us directly to:

The Meaning of Sharpness

What do we mean when we say that we want our knives to be sharp? Seems like a silly question. We all know what sharp is. Or do we?

Sharpness is not just a function of creating a super-thin edge that will readily sever free-hanging nose hairs; it’s also a function of shape and intended purpose. You could grind your chef’s knife to razor thinness, but the edge would crumble the first time you hit a bone or tried to hammer your way through a winter squash. Your knife would be sharp but useless. Similarly, a razor sharp but wedge-thick edge is great on a splitting axe but not much good for carpaccio.

We have to take into consideration the shape of the blade, the angle of the edge bevel and especially the material being cut when we consider how we judge the sharpness of our kitchen knives.

So the real question is not “how sharp should my knife be,” but rather “how do I get maximum performance from my knife under a given set of conditions.” A sharp knife can be defined as one that has a keen edge that can hold up in repeated usage while producing the results we’re looking for in the kitchen.

The Myth of Thick Edges

The theory is that thick edges (larger angles) last longer than thin edges, and the majority of the knife buying public wants the edge to last as long as possible. But it doesn’t work out that way in practice. Thinner edges actually outlast thicker edges almost all the time.

The thinner edge starts out performing better than the thicker edge. So even if it does degrade it has a lot of ground to lose before it falls to the performance level of the thick edge.

Thinner edges cut more easily, putting less stress on the edge. If a thin edge takes three slices to get through a big slab of raw meat, a thicker edge might take six or seven. Or three with a lot more force. The thicker edge is doing twice as much work, degrading twice as quickly.

Thinner edges are easier to control. Lateral stresses are a significant source of edge degradation. The more smoothly, accurately and easily you are able to cut, the less lateral stress you put on the edge.

Thin is good.

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"Some people drink deeply from the fountain of knowledge. Others just gargle." ~ Grant M. Bright