How to Flatten a Whetstone

Flatten a whetstone by drawing a pencil grid on its face and abrading the face with a flattening plate, a coarse diamond plate or coarse wet-and-dry paper on glass until every pencil line is gone. It takes about two minutes. Check before every few sessions on a soft clay stone, and much less often on a hard ceramic one.

Stones wear where you use them, and you use the middle. After a few knives the face is slightly hollow — usually a fraction of a millimetre, which is more than enough. The blade rides lower in that hollow, so the angle between edge and stone changes as the stroke crosses it. Every stroke is then a slightly different bevel, and the apex never meets cleanly.

This is why flattening belongs near the front of any honest sharpening advice, not in a footnote. It is the one maintenance task that decides whether good technique can work at all.

1. Dry the stone enough to take pencil, then draw a grid across the face — four or five lines each way, corner to corner is fine too. An ordinary HB pencil works.
2. Wet the stone and run your flattening surface across the whole face with light, even pressure, in a figure of eight or in overlapping passes along the length.
3. Stop after a dozen passes and look. Pencil remaining in the middle means a hollow. Pencil remaining at one end means the stone is wedge-shaped, which happens if you always sharpen in one direction.
4. Keep going until no pencil remains anywhere, then rinse thoroughly. You are done.

Rinsing matters more than it sounds. Flattening leaves coarse loose grit on the face, and a stray 200 grit particle on a 6000 grit stone will put a scratch across a finished bevel.

Avoid flattening one stone against another. It works, slowly, and it dishes the second stone while it does it. Avoid concrete slabs for finishing stones for the same reason — a slab is only as flat as whatever cast it.

There is a direct trade here and it is worth understanding before you buy your next stone. Soft stones release abrasive readily, which is why a King cuts well for the money and why it dishes. Hard stones hold their shape and cut more slowly, which is why a Shapton Glass suits 63 HRC powder steel and stays flat through it. Our stone picks set out the full comparison, and the grit guide explains which numbers to own.

• Flattening dry. Water carries the swarf away. Dry flattening glazes the surface and loads the plate.
• Pressing hard. Weight does not speed it up much and does tilt the plate. Light, even, many passes.
• Only flattening the coarse stone. Finishing stones dish too, and a dished 6000 undoes the work of a flat 1000.
• Leaving the edges sharp. A freshly flattened stone has crisp corners that can nick a blade or your hand. A few passes at 45 degrees along each long edge chamfers them.

Pencil grid, abrade until the grid is gone, rinse well, chamfer the edges. Do it every few sessions on a clay stone and whenever the pencil test says so on a harder one. It is two minutes of work that makes every minute of sharpening afterwards count — and it is the first thing to check when a knife comes off the stone no sharper than it went on. The full whetstone walkthrough covers the rest of the setup, and the usual sharpening mistakes are worth a read alongside it.