What "sharpen at 15°" actually means
A knife edge is two flat strips of steel, the bevels, meeting in a line. Sharpening means grinding each bevel on a stone until it meets the other one exactly, with nothing left in between. The angle in the instructions is the angle of one bevel against the middle of the blade. In practice that's how far you tilt the blade up off the stone.
The parts
- Apex
- The very edge, where the two bevels meet. On a dull knife it is a tiny rounded flat a few hundredths of a millimetre wide.
- Bevel
- The narrow strip along the edge that you grind. It's often visible as a slightly different-looking band, just 0.5–1.5 mm wide.
- Shoulder
- Where the bevel meets the rest of the blade. If your angle is too low, the stone touches here instead of at the apex.
- Face A / B
- The two sides of the blade. This app calls them A and B so it's always clear which side is on the stone.
Finding the angle without a protractor
- Spine height. Lift the spine above the stone by the height shown above. For a typical 48 mm chef's knife at 15°, that's about 12 mm, or five stacked 2-euro coins.
- Halving. Hold the blade straight up (90°), halve it (45°), halve again (≈22°), then come down a little more. That's roughly 15°.
- Angle guide. A clip-on guide or a wedge you rest the blade on while learning. You can give it up once your hands know the position.
- The marker trick. Paint the bevel with a permanent marker and take a few strokes. Where the ink comes off shows exactly where the stone touches (try it in the simulator).
Being exact matters less than being consistent. 14° every stroke beats switching between 12° and 18°.
What edges look like
Pick a condition. You get the same three ways of looking that you have in real life: a close look (a cheap loupe helps), the light test, and slicing paper. The magnified cross-section shows what's really going on at the apex.
In the side view, chips are drawn 6× deeper than real life so you can see them. Real chips worth worrying about are about the thickness of a hair or a bit more. Look for them by holding the blade edge-on against a bright window.
What the bevel looks like after each stone
Each stone replaces the scratches of the previous, coarser one with finer ones. When you change stones, keep going until the old, coarser scratches are gone along the whole edge.
The burr: your signal to move on
You can't see the apex while you grind. The burr is how you know you've reached it. As long as there is still a flat between the two bevels, you're not done with that side. Once the bevel you're grinding breaks through to the other side, the thinnest steel at the edge folds over onto the opposite face. That little flap is the burr.
How to feel it
- Stop grinding and wipe the blade.
- Lay the pad of your thumb flat on the blade, a bit above the edge, on the face opposite to the one you were grinding.
- Slide it across the edge, from spine toward edge and off. Light pressure. Never along the edge.
- A burr feels like a tiny catch or roughness right at the last fraction of a millimetre, like the edge of a sticker. The other face slides off smoothly.
- Check at the heel, the middle and especially the tip. Wherever it isn't there yet, that part hasn't reached the apex.
Some people check with a fingernail instead: drag it lightly down the face and off the edge, and it snags on the burr. On fine stones the burr gets so small that you may only see it as a faint glint under a lamp.
Practise: find the burr
Someone has been grinding this knife. Use your thumb below to find out how far they got.
Doing it for real
Everything in the simulator maps directly onto the real thing. Here's what to buy, how to set up, and the routine on one page.
What you need
Combination whetstone 1000/6000 essential
A medium side for sharpening and a fine side for refining. The single best first purchase. A 1000/3000 or 1000/4000 is just as good.Non-slip base or stone holder essential
The stone must not move. Many combination stones come with one; a damp towel underneath works too.Permanent marker essential
For the marker trick. It's the cheapest way to see your angle.Flattening stone / plate soon
Stones wear hollow in the middle, and a dished stone rounds your edge. Flatten every few sessions.Leather strop (+ compound) nice to have
Takes off the last of the burr and polishes. Folded newspaper on a flat surface, or a cork, also works for deburring.Coarse stone 220–400 only if needed
For chips or knives that are very dull. Skip it until you meet a chip.Clip-on angle guide optional
Helps while learning. Training your eye with the spine-height trick works just as well.Jeweller's loupe 20–30× optional
Cheap, and it lets you actually see burrs, chips and scratch patterns.A cheap practice knife recommended
Learn on a knife you don't care about before touching your good one.The routine
- Prepare the stone. Soaking stones: submerge for 10–15 minutes until no more bubbles rise. "Splash-and-go" stones: just wet the surface. Keep it wet throughout. The grey slurry that forms helps cutting, so don't rinse it away on the medium stone.
- Set the angle. Blade across the stone, edge facing away or toward you, spine raised to the angle (≈12 mm for 15° on a normal chef's knife). Paint the bevel with marker the first few times.
- Grind face A on the 1000. Two or three fingers of your other hand on the flat of the blade, just above the edge, over the section you're working. Medium pressure, about 1–2 kg (press on a kitchen scale once to feel it). Slow, even strokes. Work in sections: heel, middle, tip, lifting the handle for the tip.
- Check for the burr every 10–20 strokes, at heel, middle and tip, on face B. Keep going until it runs the full length. Then stop.
- Flip, grind face B the same way until the burr is on face A along the full length. This side usually goes faster.
- Refine on the 6000 with light pressure, a few strokes per side, then fewer: 5 and 5, 3 and 3, then single alternating strokes.
- Deburr. Very light alternating strokes, then a few edge-trailing strokes per side on a strop (spine leading), or slice through a cork.
- Test. Light test: no reflections. Paper: clean, quiet slice along the whole length. Then rinse and dry the knife, and let the stones air-dry.
How it should feel and sound
- Medium stone: a steady, gritty hiss and a slight drag. A grey slurry builds up. That's steel and stone particles, and it's normal.
- Fine stone: much quieter and smoother, almost slippery. Little slurry. Barely any steel comes off, so it can't fix a dull edge.
- Correct angle: the blade feels "seated", with the bevel flat on the stone. Too high and it feels like it's scraping on a point. Too low and you feel the wider blade face and nothing seems to happen.
- The burr: a faint roughness at the last bit of the edge on one face only. On the 1000 it is clearly feelable. On the 6000 it's tiny.
- Time: a dull kitchen knife on a 1000 stone typically needs a few minutes per side, often 50–150 strokes. Your first time will be slower. That's fine.
When something goes wrong
| What you notice | Likely cause | Fix |
|---|---|---|
| No burr after a long time | Angle lower than the existing bevel: you're grinding the shoulder. Or too little pressure on a fine stone. | Marker trick. Raise the spine slightly. Use the 1000, medium pressure. |
| Burr in the middle but not at the tip | The curve never touches the stone. | Lift the handle as you work the tip; work the tip as its own section. |
| Marker comes off only at the very edge | Angle higher than the bevel. | Lower the spine a little, or accept a microbevel. Fine, but be consistent. |
| Marker comes off unevenly, or a rounded-looking bevel | Angle changes during the stroke (rocking). | Lock the wrist, move from the shoulder, slow down. |
| Feels sharp, but dulls after a few cuts | The burr was left on and folded over. | Deburr properly: lighter alternating strokes, strop, then check both faces. |
| The burr keeps flipping and never goes away | Pressure too heavy during deburring. | Almost no pressure, single alternating strokes, edge-leading, then strop. |
| Paper tears at one spot | A dull spot or chip there. | Light test to locate it, then grind that section until it has a burr too. |