Knife Sharpening Presented by J.D. Swanepoel Swan Knife Sharpene - - PDF document

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Knife Sharpening

Presented by J.D. Swanepoel

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Knife Maker

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Artist?

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The Meaning of Sharpness

Sharpness is not just a function of creating a super-thin edge. It’s also a function of

• 1. Shape of the cutting edge
• 2. Intended purpose of the knife

So the real question is not “how sharp should my knife be,” but rather “how do I get maximum performance from a 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.

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A High Performance Edge

A knife should cut as easily as possible while still maintaining its integrity and staying sharp. For maximum performance the edge must be as thin as possible for efficient cutting However, a thin edge can be damaged easily. The challenge: To thin the edge as much as possible, but not so much that it is regularly damaged during hard use.

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Knife Edges

V-edge Very sharp but susceptible to damage Double bevelled edge Very sharp but with added strength Chisel edge Extremely sharp and quite tough Convex edge Very sharp with a strong edge

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Basic Sharpening Principles

The basic principles are the following: Burr Sharpening Angles Abrasives Consistency Sharpening strategy These principles apply no matter what sharpening method you choose.

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The Burr

A burr (wire edge) is a rough, almost microscopic, raised lip of metal that forms when

• ne edge meets the other.

It is the only way to be absolutely certain that you have fully ground an edge. You must feel a burr running all the way from heel to tip to know that you have fully ground that side of the knife.

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Sharpening Angles

General Kitchen Work 5 to 20 degrees per side (10 to 40 degrees total) Meat cleavers 20 to 25 degrees per side

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Sharpening Angles Continued

Back bevel (relief) – 15 degrees Primary edge - 20 degrees 15/20 Double Bevel

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Abrasives

In essence you sharpen a knife by scraping away metal by using abrasive stones and other materials which come in different shapes and sizes Natural Rock stones Natural Water stones Synthetic Waterstones Synthetic Aluminium Oxide stones Synthetic Silicon Carbide stones Diamond “stones”

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Abrasives continued

Variety of grits - very coarse to ultra-fine. Grit refers to the size of the individual particles of abrasive in the sharpening stone. Below 300 Coarse 300 - 400 Medium 600 - 800 Fine 1200+ Ultra Fine

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Abrasives continued

Lubricants for Abrasives Which is better - Oil or Water? The purpose of a sharpening stone is to grind the edge and remove metal. Oil reduces friction and makes the process much slower. Waterstones wear very quickly, revealing new layers of cutting abrasive. In both instances – oil or water – swarf builds up as you sharpen and clogs the pores of the stone. Swarf - a mixture of oil / water with metal filings and stone grit.

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Consistency

You must be able to maintain a consistent angle while you are sharpening. Maintaining a consistent angle whilst doing freehand sharpening with bench oil stones or water stones is extremely difficult. Using a sharpening system where angles can be maintained constantly is a definite advantage.

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Sharpening Strategy

Coarse versus Polished Edges The finer the stone you use to sharpen a knife, the more polished the edge will be. However, leaving the edge of your knife just a little coarse can be an advantage… Push cutting and slicing comparison Push cutting involves pressing the finely polished edge through the fibres of the food, pushing them to either side (slicing carrots). Slicing involves severing fibres and requires a toothier

• edge. A soft tomato, roast chicken – anything with an
• uter layer that is tougher than the much softer

inside demands an edge that can bite into the skin without crushing the interior.

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Sharpening Strategy continued

If you have a knife that is only used for push cutting, you can take it to a very fine, highly polished edge. The negative side: The thinner the edge, the stronger it will need to be to avoid excessive damage. A dedicated slicer can be finished on a medium-fine grit stone, leaving the edge slightly coarse (micro-serrations). . The negative side: A coarse edge wears more quickly and requires more maintenance. Create a dual edge on your knife? Slightly coarse section at the back of the blade near the

• bolster. The rest of the blade fine or extra fine.

A toothy section for cutting through tough materials as you begin your stroke and a finer edge for push cutting through the rest.

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Sharpening Steps

For the sake of discussion, let’s put a 15/19 degree double bevel on a knife. Step 1 Establish the 15 degree angle on the knife sharpener. For this step a coarse stone will be needed. This might take a while. To grind off the shoulders of the previous edge will require the removing of a lot of

• metal. That’s why a coarse stone is needed.

To keep the edge balance of the knife, you’ll want the bevels (edges) relatively even on each side. If you just grind one side until you get a burr, the other side will require much less grinding. Thus the bevels (edges) will be mismatched.

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Sharpening Steps

Step 1 continued To keep the edges matched, grind one side for about five minutes, then switch to the other side, maintaining your 15 degree angle. Feel the knife every so often to see if you can feel a burr. To dress up the scratch pattern, switch to your fine stone and give the edge several passes on each side (at the same angle) to polish them out .

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Sharpening Steps

Step 2 Establish the 19 degree angle on the knife sharpener. Switch to a medium stone. Create a burr again at the new sharpening angle. This will happen very quickly - most of the metal which needed to be removed has been removed in step 1. Keep the edges matched. Do a number of strokes one side, then switch to the other side.

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Sharpening Steps

Step 3 Switch to a fine stone. Keep the edges matched. Do a number of strokes one side, then switch to the other side. Keep stroking side to side until all the scratches from the medium stone are gone. If you have a very fine stone (I use a 1200 grit stone) you can do a couple of strokes per side from heel to tip

• f the stone.

Use a magnifier to check the edge of the blade.

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Sharpening Steps

Step 4 Stropping Stropping is a final way to finish off a burr or put a final mirror polish on your edge. Stropping is normally done using a flat piece of leather. Stropping is an edge trailing stroke. Lay your knife flat

• n the strop with the spine facing away from you.

Slowly pull the knife toward you while lifting the spine.

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Sharpening Steps

Step 5 Be Patient Sharpening a knife takes time and patience… Focus Focus on what you are doing Loss of concentration could cause severe injury! Add a Disclaimer Neither Swan Knife Sharpeners nor JD Swanepoel will accept any responsibility for any accident or injury which may occur during the process of sharpening a knife or during the use of a sharpened knife. .

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Steeling a Knife

Steeling could be a critical part of maintenance one can perform on a knife. The steel realigns the edge of the knife, forcing the rolled spots back into line. Use a smooth steel – a grooved steel acts as a file, knocking microscopic chips out of the edge. .

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Is the Knife Sharp?

Remember that we defined sharp not only as two edges intersecting at a line of minimum width, but also as a function of blade shape, angle and the material to be cut. We want a keen edge that can hold up in repeated usage while producing the results we’re looking for in the kitchen. The best test, though, is actually using the knife for its intended purpose. If you have a slicing knife, try a soft tomato.

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Why Edges Wear

Strength - resistance to low-impulse deformation (bending). Strength is directly related to the hardness of the steel. Toughness - resistance to high-impulse deformation – impacts, chipping and cracking. Wear - a knife blade encounters abrasive materials and the edge wears away. Indenting and rolling - as pressure is put on the edge

• f a thin blade, the edge can indent, impact or roll over

to one side or the other. Chipping - the edge can chip or crack under impact Corrosion - micro-rusting and acidic foods can lead to edge loss. Technique – knife handling by individuals

QUESTIONS

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