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How To Sharpen a Knife

How To Sharpen a Knife

 
There are more non-functional knife sharpeners on the market than any other product (with the possible exception of no-effort exercise machines). However, there are plenty of ways to sharpen a knife that do work. This article points out the most common mistakes and offers links to resources.

Steps

  1. The mistakes that are commonly made in sharpening knives are uncontrolled bevel angles, failure to establish a new edge, and leaving the final bevel too rough.
  2. Pick an angle to sharpen your knife. If you already know what angle your knife is sharpened at, you probably wish to sharpen at this angle again. If you don't know your angle but wish to, ask the manufacturer of your knife or inquire at a knowledgeable knife shop to determine what angle is appropriate for your knife. Otherwise, you must make a decision: choose an angle of 10°-30° per side; shallower angles make a sharper edge that doesn't last as long, steep angles are more durable, 15 to 20° is a good compromise: select an angle that matches the use the knife will receive. When shopping for a sharpening system, make sure it provides an edge guide mechanism that supports at least a couple of different angles.
  3. If available, use an angle guide to control your edge's angle. Otherwise, you will have to control the angle by hand, which is hard and requires a well-formed perception of angles.
  4. For a symmetrical edge, sharpen the knife by dragging it across the lubricated (with oil or water) stone in the opposite direction you would move it to slice a thin layer off the stone. This allows a burr to form and prolongs the stone's life.
  5. Continue grinding at this angle until your grind goes roughly half way through the steel. This doesn't need to be precise, just guess. For a one-sided edge ("scandi grind", "chisel grind", etc.), skip to step number 6.
  6. Flip the knife over and sharpen the other side of the blade until you create a new edge; the easiest way to determine that you have removed enough metal is to sharpen until you have raised a "burr", a feature that steel will naturally form when one bevel is ground until it meets another. It will generally be too small to see, but you can feel it scraping/catching on your thumb if you stroke away (dull side of the knife to the sharp) from the edge. Finer stones produce smaller burrs, but they are still there.
  7. If you do not remove enough metal to create a new edge, you will leave some of the dull edge in place. A dull blade (or a blade with dull spots or nicks) will reflect light from the very edge of the blade. A razor sharp knife edge will not show "bright spots" when you hold it blade up under a bright light. You will need to remove enough material from the sides of the bevel so that the edge stops reflecting light.
  8. Flip the knife over and sharpen the other side of the blade in a similar fashion.
  9. Remove the resulting burr by "cutting into" a hone (a finer stone). That is, still holding the blade at the same controlled angle, move the blade in the opposite direction you moved the blade in steps 4-8. Some people feel this step should be done with a dry stone for reasons beyond the scope of this article.
  10. If you wish, you may further polish or even strop the edge to the desired sharpness. This makes the edge better suited for "push cutting" (cutting directly into materials, pushing strait down without sliding the blade across the object) but generally impairs slicing ability: without the 'microscopic serrations' left by grinding with a stone, the blade tends to not bite into things like tomato skins.
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Tips

  • Sharpening stones work best with a lubricant to help keep the stone free of particles. Use either an oilstone with a neutral oil such as mineral oil, or water stones with water. Once you start using a stone with oil, you cannot switch to water.
  • Some experts recommend sharpening as if trying to slice a thin layer or decal off the stone. Don't do this: it is bad advice; most people don't hold the correct angle this way. You instinctively raise the blade until you feel and see the edge working. This creates larger edge angles and thicker bevels as time goes on and the results gradually deteriorate. The more you sharpen, the duller it gets. Sound familiar?
  • Electrically powered stones and grinding wheels need to be used with great care. Heat generated by the stone while grinding with these devices can anneal (soften) the steel, causing the knife to dull quickly with use. An exception to this is the machines developed by CATRA, The Worlds Cutting Technology Organisation, these use special abrasive wheels which keep the cutting edge cool and so have excellent blade edge life.
  • Cheaper stainless steel kitchen knives won't hold an edge well; don't get discouraged - it may not be your sharpening technique. They will sharpen just fine, but will dull very quickly. What's happening is that the edge is rolling over because the steel is soft. Try using a steeper sharpening angle or a knife with harder steel.
  • The best angles to sharpen a knife are 19-22 degrees. But really you should match the original rough grind of the blade.

Warnings

  • Don't drag your fingertip across the newly sharpened edge to see if it is sharp. A better test is to try to cut a single piece of newspaper while holding the paper loosely between two fingers.
  • Always be careful around recently sharpened knives (and all knives in general) for knives are one of the causes of accidents around the house

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Article provided by wikiHow, a wiki how-to manual. Please edit this article and find author credits at the original wikiHow article on How to Sharpen a Knife. All content on wikiHow can be shared under a Creative Commons license.

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