Sharpening

Sharpening is the process of creating or refining a sharp edge of appropriate shape on a tool or implement designed for cutting. Sharpening is done by grinding away material on the implement with an abrasive substance harder than the material of the implement, followed sometimes by processes to polish the sharp surface to increase smoothness and to correct small mechanical deformations without regrinding.

There are a wide variety of ways of sharpening tools. Malleable metal surfaces such as bronze, iron and mild steel may be formed by beating or peening a flat surface into a sharp edge which incidentally causes work hardening.

More commonly, an abrasive material may be rubbed against the cutting edge to be sharpened. The most traditional material is a natural stone such as sandstone or granite, but modern synthetic grinding wheels and flat sharpening stones can be manufactured in precise grades of abrasiveness according to the intended process. Finally, a sharp edge may be 'dressed' using a Honing steel

The substance on the sharpening surface must be harder (hardness is measured on the Mohs scale) than the material being sharpened; diamond is extremely hard, making diamond dust very effective for sharpening, though expensive; less costly, but less hard, abrasives are available, such as synthetic and natural Japanese waterstones. Several cutlery manufacturers now offer electric knife sharpeners with multiple stages with at least one grinding stage. These electric sharpeners are typically used in the kitchen but have the ability to sharpen blades such as pocket or tactical knives. The main benefit of using an electric sharpener is speed with many models that can complete the sharpening process in one to two minutes. The disadvantage is that the sharpening angle is fixed so some specialized knives, like a Japanese style Santoku, may need additional attention to sharpen to the ideal angle.

Very sharp knives sharpen at about 10 dps (degrees per side) (which implies that the knife's edge has an included angle of 20-degrees). Generally speaking, razors, paring knives, and fillet knives should be the sharpest knives at an angle of 12° – 18°. Most kitchen knives, like utility/slicing knives, chef’s knives, boning knives, carving knives, should be sharpened to 15° – 25°. The exceptions are Japanese style knives that are usually sharpened to 14° – 16° depending on the knife maker. Japanese style knives utilize a much harder steel, and are therefore more brittle than their Western style counterparts. This means care should be taken when handling these knives as they are susceptible to chipping and breaking. The sporting knife category, including pocket knives, survival knives, and hunting knives, sees more intense action and should be sharpened to the 25° – 30° angle range. The less sharp angle means there is more metal there to cut, thus providing more durability out in the field. For an extremely durable edge, a machete, chisel, drawknife or ax should be sharpened down to 30° – 40° providing even more ruggedness and longer lasting sharpness.

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Wikipedia