How to minimize edge chipping on knives

posted in: Knife Care, Knife Use | 0

Knife design involves a lot of compromise, not only with the choice of steel but with basically all the materials. There are trade-offs between hardness, and ruggedness, edge holding and price. And on it goes.

For a lot of people, though, a knife is just a slab of steel with a sharpened edge. What’s the big deal? In that vein, let’s look at why knife edges chip.

It’s simple: thin, hard edges chip more readily than thick soft ones. If your blade is a no-name, relatively soft (52-54 Rockwell C) stainless steel, chances are it’s sharpened at 20 or more degrees per side from the factory. If you try to crack open brazil nuts with it, the edge will dull and may bend from the forces applied, but not break. Whack a nut with a hard and thin-ground Japanese blade (around 63 RC) and there will be blood, knife blood: pieces broken right out of the edge.

We harden the S35VN steel we use to about 60 RC and for everyday use we sharpen it to about 12 degrees per side because the alloy is strong and will handle a thinner edge than common knife steels. We’ve even sharpened our Sitka Santoku down to 9 degrees per side and not had edge chipping in everyday kitchen use, providing the knife is not abused. On the other hand, our fillet knife sharpened at 10 degrees per side may experience edge chipping due to the fine rib bones it constantly faces. We find that 12 degrees per side is a sweet spot where cutting is still very aggressive but edge chipping is minimized.

To avoid chipping, the answer usually comes down to the edge angle, since no matter whether it’s an axe or a razor blade, if they have the same edge angle and the same steel, the very edge will be equally vulnerable to damage. You have to increase the edge angle as the forces behind the edge increase if you want to avoid damage to that edge. Obviously, heavy-use knives also typically have heavier blades. For instance, a metal shear will have a thick blade to distribute the heavy forces without buckling and a large angle to provide as much supporting material as possible at the cutting edge.

If you find that your knives are developing small chips at the edge in regular use, we suggest you first try to avoid the problem by using a beater knife for the damaging tasks and if that’s not practical, get out your sharpening equipment and re-profile your edge to a steeper angle. If it was 12 degrees per side before, step up to 15/side and see if that solves the problem. Experimentation is in order. You don’t want to go any higher than needed with the angle because this rather rapidly reduces effective sharpness as you go above 12 degrees/side.