How to Hollow Grind a Knife Blade
Hollow grinding is the creation of a concave or hollowed channel along the cutting edge of a blade. This technique is used on blades that require a much sharper edge than is possible with a simple convex bevel, including such applications as razors and surgical scalpels. It's not an easy technique to master, but with practice it makes a more useful and sharper blade.
Things You'll Need
- Bench grinder
- 50, 120, 220 and 400-grit wheels
- Bucket of water
- Micrometer
Instructions
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1
Determine the appropriate grind depth. For most blades, the grind on both sides of the knife should add up to about one half of the blade's thickness. Use a micrometer to measure the thickness of the blade, then divide the result by 4 to find out how deep the grind should be on one side.
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2
Pass the blade's intended cutting edge over the grinding wheel. A hollow grind is not the edge itself; the grind should reach the edge of the blade stock, but the deepest point will be further back into the stock. Apply light, even pressure throughout the pass and make sure to follow the contour of the blade from the start of the grind to the tip.
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3
Dip the blade in water after each pass to mitigate heat buildup. If you don't, you run the risk of warping the blade. Measure the grind depth at the deepest point after two to three passes with a micrometer, then switch sides.
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4
Apply the same grind depth to the other side of the blade. Quench the blade and measure with a micrometer after each pass to keep on track. Repeat on both sides of the knife until approximately one-half of the required depth has been reached.
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5
Switch to a 120-grit wheel and make two to four light passes on both sides of the blade, quenching after every other pass. This will remove more stock, but it also starts to polish the steel.
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6
Switch to a 220-grit wheel and make two to four more passes on both sides of the blade. The last bit of stock removal should occur here.
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Switch to a 400-grit wheel and make two passes on both sides of the blade, quenching after every other pass. Continue doing this until the majority of scratches have been worked out.
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Tips & Warnings
Most knifesmiths use belt grinders instead of wheel grinders. This is largely a matter of convenience; it's easier to change a belt than it is to change a grinding wheel, and belts are often cheaper than wheels.
Practice on scrap steel before attempting to grind a knife blade.
Always wear hand and eye protection when working with grinding tools.
References
- Photo Credit Hemera Technologies/PhotoObjects.net/Getty Images
