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Forging Knives |
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Updated
For a knife to work well, the various blade thicknesses and angles should be in proportion. A rugged survival knife necessarily has different proportions than a sushi knife. When a knife is intended for hard use, the angles and thicknesses grow. Conversely, for fine cutting, angles and thicknesses diminish. We've set up a system whereby the edge thickness, as measured by a wire gauge, sets all the other parameters --angles, thickness and so on. The concept is that a knife is an implement which supports a cutting edge, hence it's thickness should dictate the geometry of the blade.
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There are three angles: 1) Blade Angle, which is measured by the protractor. 2) Edge Angle, which is the general profile of the edge and for the most part is what's measured by the Wire Gauge. 3) Sharpening Angle, which is the outer most portion of the edge, it's the actual cutting edge. The Blade Angle is set during the forging of the blade, while the other two angles are set during finishing and subsequent sharpening. Formulas for Angles: Blade Angle = 25-AWG |
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Correlation between edge thickness (AWG) and blade angles
These are the TOTAL angles, not half angles, not the angle to the center of the blade.
AWG #9 is an edge thickness of 0.102" which is approaching axe-like proportions and such blades should be made of 1/4" stock or greater. AWG #21 is a thickness of 0.028" and might be found on fine kitchen knives with a blade thickness of somewhere around 0.060".
What follows is a different method of sharpening--one where the abrasive is moved rather than the blade.
Sharpening Table
Unless you're going into the sharpening business it's probably easier and cheaper to use silicon carbide wet/dry sandpaper. Use it dry. Sharp starts to happen at about 400 grit. Ultra-sharp starts at about 1000 grit. Above 1000 grit it should probably be called edge polishing and a side to side motion (along the edge rather than across it) works well. For this photo the stone is holding the blade in position. While sharpening one hand is on the stone, the other on the knife handle.
Sharpening Table Angles required to achieve the Blade Angles of Table 1
Formulas for Sharpening Table Angles:
Edge Angle = 32-AWG
Sharpening Angle = 38-AWG
It should be apparent by now that each step in wire gauge translates to a one degree angle in blade geometry.
We'll start by sharpening the 1018 Knife previous forged and in the process clear up some misunderstanding about knife edges. Sharpness and wear resistance are two entirely different things. Sharpness and cutting ability is almost solely dependent on blade geometry. The composition of the steel, heat treatment, etc., have virtually nothing to do with the sharpness of a blade. How long a blade will stay sharp is another matter. Now we're talkin' wear resistance and that's all about the things we just discounted.