Knife Sharpener
SHARPENING THEORY: Several things - blade thickness, blade shape, edge angle, edge thickness and edge smoothness, determine cutting ability.
Blade thickness is set by the manufacturer and has a great effect of slicing ability. Your hunting knife will never slice like a filet knife or a kitchen knife, no matter what you do to the edge. It is possible to change blade thickness a little near the edge, but that can make a big difference in cutting ability.
Blade shape likewise is set when the blade is made and is determined by the usage. For instance, more belly or curve helps skinning and filet knives slice, while a reverse curve is needed on a linoleum knife. Blade shapes like serrations and reverse curves give an aggressive look to fantasy knives.
Serrations help with some cutting chores by letting the edge attack repeatedly from different angles, always slicing the material a different point. This lets you cut with less pressure. In my opinion serrated edges are desirable for three cutting tasks - slicing tomatoes, slicing bread, and cutting rope. All other tasks are done as well or better with a plain edge (sometimes called a fine edge). A plain edge is also easier to maintain.
Sharpening is about the remaining three items - edge angle, edge thickness and edge smoothness. Edge angle is measured between the center of the blade and the bevel or flat cut by the stone. Most Western knives are double bevel, so the total angle at the edge is twice this angle. Asian knives and woodworking tools are single bevel, and the resulting smaller angle can make them aggressive cutters. That is why sashimi knifes seem so sharp.
Edge angles can vary from 10 degrees to 40 degrees, but most are between 15 degrees (filet knives) and 30 degrees (survival knives). Different angles are suited for different tasks. What's suitable in the kitchen will not do for camping. Twenty degrees is about right for kitchen knives, twenty two degrees is good for pocket knives, and twenty five degrees gives a long lasting edge to a camp knife. A good starting point is to duplicate the angle the maker put on the blade. Edge angle is difficult to measure after the fact, but is fairly easy to control when sharpening by controlling the angle between the stone and the blade.
Any edge thickness under a few thousandths of an inch may be considered sharp. Paper is about 2 to 3 thousands thick and will cut you if conditions are right. Edge thickness naturally increases with wear.
Ideally the flats cut by the stone would come together to make a perfect edge with zero edge thickness, but edge thickness is limited by several factors. First is malleability, or the tendency for steel to move when it is pushed. The yield strength of steel is thousands of pounds per square inch, but as the edge thickness approaches zero, it takes only a fraction of an ounce to move it. The force of your hand with a stone or steel can move enough steel to create or smooth a burr.
Knives-Sharpeners Information Posted By: Blueshoots.com