How to Sharpen a Dull Knife: Repair Dull and Chipped Edges With a Pull-Through Sharpener

Start in the coarse slot with two or three light pulls, heel to tip, to grind a fresh edge. Then give it several pulls in medium and three to five light pulls in fine. Wipe the edge on a cloth and slice copy paper to confirm it cuts again.

In most cases, yes. A knife that slides off a tomato has usually just lost the thin line where the two sides meet, and the coarse slot regrinds it. Knives that are bent, cracked or missing a tip are the exceptions.

Hold it edge-up under a light and look down at the edge. A dull edge shows a thin bright line along its length. A chip shows as a notch or gap. If the knife bites a tomato but drags on paper, it is only mildly dull.

The 3-Stage costs $29.99 and the 4-Stage costs $34.99, with free shipping on both. One unit covers the full repair: coarse to rebuild the edge, medium to sharpen and fine to polish.

Yes, for straight double-bevel kitchen knives. The coarse slot is built to repair a dead or chipped edge, and the medium and fine slots finish it. It is not for serrated or single-bevel knives, however dull they are.

A few minutes. The repair is two or three pulls in coarse, several in medium, and three to five in fine, plus a wipe and a paper test. A knife with a chip may need the coarse step repeated over a few sessions.

Grind the whole edge back until the notch disappears. Give it two or three light pulls in coarse, check the chip, then finish in medium and fine. If the chip remains, repeat coarse another day rather than pressing harder. Small nicks usually go in a few sessions.

It removes more steel than the other slots, which is why it gets only two or three pulls and only for repair. Used that way, it rebuilds the edge without costing much blade. Using coarse for every session would wear the knife down faster.

Both have the same coarse repair slot. The 3-Stage at $29.99 handles the full repair. The 4-Stage at $34.99 adds a second finishing pass, which smooths the edge further after heavy coarse work.

No. It is manual and works dry, with no batteries, water or oil. Place it on a dry counter, hold the handle, and pull the knife through by hand, even for a heavy repair.

Treat it like any small chip: two or three light pulls in coarse along the full edge, heel to tip, then medium and fine. Keep the pull smooth as the tip leaves the slot. If the tip itself is broken off, the knife needs a professional instead.

When the chip is large enough to see from a distance, the tip is snapped, the blade is bent, or there is a crack in the steel. Those need a sharpening service or a replacement. This tool handles dull edges and small nicks only.

Rest the blade on a ripe tomato and draw it across without pushing down. A sharp knife bites into the skin at once. A very dull one slides over it or squashes the fruit, which tells you to start the repair in coarse.

Because the edge has rounded or flattened. A sharp edge meets in a fine line that is almost invisible when you look straight down at it. A bright line means the apex is worn, and a bright spot means a local dent or nick.

No. It is not for serrated knives, even very dull ones. The slots are shaped for straight edges and cannot reach between the teeth. A bread knife needs a tapered tool made for toothed edges.

Only if it is double-bevel, like most home santoku knives. Single-bevel Japanese knives such as a yanagiba, deba or usuba cannot go through it at all. Check that the edge is ground on both sides before starting.

No. Heavy pressure removes more steel than needed and can leave a wavy edge. Keep pressure light and even, and let the coarse slot do the work. If more repair is needed, add another session rather than more force.

Check the edge under light again. If the bright line is gone but paper still snags, return to medium for a few pulls and finish in fine. If a bright line remains, one or two more coarse pulls may be needed, then medium and fine.

Finish every repair in fine with three to five light pulls, then wipe the edge on a folded cloth. That clears the burr, which would otherwise fold over after a few cuts. After that, regular medium-and-fine touch-ups keep it from getting that dull again.

Yes, as long as it is a straight double-bevel knife. Inexpensive knives respond well to the coarse, medium and fine sequence. Keep the pressure light, since softer steel gives way quickly under force.

A repair produces more filings than a quick touch-up. Tap them out over a bin, wipe the body dry, and wipe the knife blade as well. Keep the sharpener out of the sink and the dishwasher.

One sharpener in the version you ordered, 3-Stage or 4-Stage. It needs no extra parts, power, water or oil. The knives and props shown in the photos are not included with the order.