8. How to sharpen a Kezuriki (削り器を研ぐ)

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Various whetstones used to sharpen knives, including natural water stones and Nagura stones.

To remove the blade, hold the shaver so that the sharp edge of the blade is facing up, and hit the bottom of the plane with a mallet. You may need to hit the plane quite a few times. This will not damage the plane as both the mallet and plane are wooden.

Before beginning to sharpen the blade, prepare and soak sharpening stones as usual.

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The lower part of the plane (kanna (鉋) of the Kezuriki (削り器) is hit in the direction of the blade to remove the blade.

As with many other Japanese blades, the blade of the Kezuriki is single beveled (just sharpened on one side). This means that one side is angled and the other side is completely straight. After sharpening the angled side, we will need to re-straighten the straight side.

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The blade is flat on one side (known as the Uraoshi surface/裏押し). Sharpening and pressing the angled surface of the knife completely down on the sharpening stone as you will damage the blade by pushing the Shinogi line (しのぎ筋/しのぎすじ) backwards.

After preparing your sharpening stones, place the blade, angled surface down, and hold firmly with both hands so that the surface of the blade is evenly pressed against the stone. 

Sharpen the blade by pushing it backwards and forwards, applying pressure when pushing the blade forward and releasing pressure when pulling the blade backwards. The action of pushing the blade forwards shaves and shapes the blade into shape, and the pulling motion only returns the blade to its original position.

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The blade of the Kezuriki (削り器) should be held firmly with both hands to ensure the entire surface of the blade is evenly pressed against the stone.

You do not want to press the angled surface of the knife completely down on the sharpening stone as you will damage the blade by pushing the shinogi line (しのぎ筋) backwards (see diagram).

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The wrong angle when sharpening the blade of a Kezuriki (削り器). Pressing the blade completely down will push the Shinogi line (しのぎ筋/しのぎすじ) backwards.

Instead, keep a small angle between the blade and the sharpening stone. This angle should be maintained throughout the sharpening of the knife. You can tell if the angle you are using is varying based on the sound. A constant sound means that a constant angle is being maintained and a changing sound means you are not holding the blade at the same angle whilst pushing and pulling.

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The correct angle when sharpening the blade of a Kezuriki (削り器).

Just as you do not want to flatten the blade completely on the stone, you also do not want to angle the blade too far upwards. The higher the angle of the blade, the sharper the blade becomes, and the easier it is for it to go blunt. You want your sharpening to last as long as possible and not sharpen the blade every time you use it, striking a balance between sharpness and durability.

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The wrong angle when sharpening the blade of a Kezuriki (削り器). Lifting the blade too high will cause the sharp edge to wear out quickly with use.

As with sharpening all blades, start on a low grit stone before gradually moving to a higher grit polishing stone. For me, I start with a stone that’s around 1500, then move up to 3000 and finally use an 8000 finishing stone.

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Removing the burr on a single beveled blade of a Kezuriki (削り器). Pressure should be applied evenly across the surface.

When the angled side has been sharpened, a burr will form, protruding over to the flat side. The final sharpening step is to remove this burr making the sharpening even.

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Removing the burr on a single beveled blade of a Kezuriki (削り器). Pressure should be applied evenly across the surface as the blade is pushed up and down.

To do this, hold the blade flat against the stone, slide the blade back and forth, flattening out the burr. Repeat for around 3 minutes or until you can no longer feel the burr.

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To replace the blade, insert the blade with the flat side facing down. Gently push the blade in as far as it goes. Turn the plane around and tap it facing against the direction of the blade. Try to tap the centre of the plane to make the plane go in evenly. If you miss, tap the plane on the left or right side to even out the plane. If the blade goes in too deeply, tap the plane on the opposite side to get it to come back out, as mentioned above.

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For information on how to shave Katsuobushi using a Kezuriki, click here.

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