- Powered grinding wheel
- Eye protection
- Gun oil
Grinding a knife is not the same as sharpening or honing it. The difference is that grinding removes large amounts of metal from the knife's blade, changing the cross section shape. Hollow ground knives are typical for extremely sharp combat blades made for slicing as well as high quality kitchen knives. When you're hollow grinding something you're essentially changing the shape of the knife's edge, decreasing its angle by grinding away the metal slope behind the edge. This makes the edge more shear and narrow so it will cut more easily. The downside to this is that because there is less metal making up the blade, it becomes damaged and dulled much more easily through simple use.
Study the knife you intend to hollow grind. Look at it edge-on in a well-lit environment. What you're trying to identify is trough, or the contour along the sides of the knife where the blade's angle deepens before sloping down to the cutting edge, which will be placed along the center of the grindstone. By grinding there, you push the trough further toward the back of the knife. This decreases the overall angle from the trough to the edge, creating a thinner profile and that characteristic hollow which is the style's namesake.
Put on your gloves and eyewear and start your grinding wheel. If it's a variable speed model, place it on the lowest setting possible to reduce the chances of the blade being ripped from your hands while you're grinding it. Hollow grinding will take more time this way, but you'll get better results.
Coat the sides of the knife with a thick layer of gun oil. This ensures that the knife will not discolor or loose its temper. If it's a self cooling grinding wheel, it should cover itself with a thin film of water to prevent the knife from sparking or heating excessively and you will not need to oil the knife.
Hold the knife handle in your main hand and the back of the tip in your off hand. Place the trough flat against the grindstone and draw it from the hilt toward the tip of the blade in a smooth stroke. Remember to keep the trough horizontal with the ground at all times, so a curved blade will take some maneuvering to get right.
Flip the knife over so the handle is in your off hand and repeat the stroke. Depending on the quality of the steel you may need to repeat this between 3 and 10 times. Make sure to keep the strokes even on both sides to maintain symmetry and balance. After each set of strokes, examine the knife again by eye, and repeat until the trough has been pushed back the desired distance from the knife's edge.