How to Sharpen Chisels and Plane Irons

Lie-Nielsen puts it in one line: a sharp edge is the intersection of two polished surfaces. For a chisel or plane iron those surfaces are the flat back and the bevel (see the plate above). Veritas adds the point that saves the most time: only the cutting edge itself does any cutting, so only the last fraction of the bevel needs to be honed.

Sharpening therefore has three parts: make the back flat and polished near the edge, hone a bevel that meets it cleanly, and remove the burr that forms where they meet. Grinding comes in only when the bevel needs reshaping.

The back is prepared once, when a tool is new or restored, and then kept polished. Veritas suggests lapping it on an 800 or 1000 grit water stone (250 grit only for a very wide blade), keeping it flat so that no back bevel forms, and polishing it on a 4000 or 8000 grit stone. It need not be flat along its whole length — particularly on a plane iron — but it must be flat near the edge.

Chisels need more care than plane irons, because a chisel’s back is its reference when paring. Lie-Nielsen prepares chisel backs by working across the honing stone, then a medium 3000 grit stone, then the finishing stone, honing on and off the edge of the stone so the front of the back is never rounded. It notes that a slightly concave back is better than a convex one. Japanese chisels take this further: their backs are hollow-ground behind a flat rim, which Covington & Sons explains makes the hard steel layer easier to sharpen and keep flat.

Most methods use two bevels. The primary bevel is ground to shape the tip; the secondary (or micro-) bevel is honed a few degrees steeper at the very edge. Honing only the small secondary bevel is quick, and it puts the sharpening effort where the cutting happens. Veritas recommends that the primary bevel extend at least 1/8 in back from the edge.

Harder use calls for a steeper edge. Lie-Nielsen advises a higher secondary bevel for very hard woods, and suggests much steeper angles — 45–50° — on a bevel-up plane in difficult grain.

Sharpening moves from a coarse abrasive, which shapes the steel fast and leaves deep scratches, to finer ones that remove those scratches and polish the edge. The exact numbers matter less than the sequence: Lie-Nielsen, which uses 1000, 3000 and 8000–10,000 grit water stones, says the important point is to use a coarse (and for chisels a medium) and a fine stone, and that soft, hard and black hard Arkansas oil stones can serve instead.

Grit numbers are not comparable across systems. The same number means a different particle size in the FEPA P system used for European coated abrasives, the CAMI system used for American coated abrasives, and the JIS system used for many Japanese abrasives and stones — and the systems do not even measure size the same way.

Honing the bevel pushes a thin sliver of steel over onto the back — the burr, or wire edge. Its appearance is the signal that the bevel now meets the back along the whole edge. Lie-Nielsen hones on a 1000 grit stone until a wire edge forms, typically about four strokes, then about four or five strokes on an 8000–10,000 grit stone.

The burr is removed from the back, and here chisels and plane irons differ.

A honing guide holds the blade at a fixed angle to the stone. On a side-clamping guide, the angle is set by how far the blade projects in front of the guide: the further it projects, the lower the angle. The distance for a given angle depends on the guide’s own dimensions and on the blade’s thickness, so there is no universal figure.

Lie-Nielsen suggests a simple stop block for each angle you use, so a blade can be reset to the same projection without measuring. The Veritas Mk.II guide does the same job with a registration jig that sets the projection for the chosen angle, and an eccentric roller that adds a 1–2° micro-bevel without resetting the blade. Veritas also warns that lifting the roller off the stone raises the angle at the very edge.

Sharpening freehand works too, once you can hold a steady angle; a guide makes the angle repeatable while that skill develops.

• Chisels need a genuinely flat back, because paring references it. No back bevel, no ruler trick.
• Plane irons only need a flat, polished area near the edge, and can take the ruler trick. Some are honed with a slight curve (camber): Lie-Nielsen describes producing about 0.002–0.005 in of camber by varying finger pressure, and notes that others — shoulder planes and jointer planes among them — need a straight edge.
• Mortise chisels and other thick blades may need different jaws or settings on a guide; check the guide’s instructions.

Frequent touch-ups need only the finishing stone. Lie-Nielsen notes that to raise a new wire edge you go back to the honing stone, and that as the secondary bevel grows it takes more strokes to raise one — the signal to re-establish the primary bevel. When you do, it suggests leaving a trace of the old secondary bevel (about 1/64 in), which helps keep the edge square. A nicked or chipped edge also needs the coarse abrasive, to grind back past the damage.