Why sharp is safer
It can sound backward, but a sharp tool is generally safer than a dull one. A dull edge needs more force to cut, and force is what makes a tool skid, slip off a line or jump out of a cut and into a hand. A sharp edge slices with light pressure, which is easier to control.
Sharp edges are also unforgiving if you are careless. Keep both hands behind the cutting edge, clamp the work, never pull a chisel toward your body, and wear eye protection. Store sharpened tools so edges are covered or separated, and never test sharpness with your thumb across the edge; instead, test on a scrap of wood or a fingernail surface at a very light touch, or simply see how a shaving curls. If you are setting up a bench for this, a safe home workshop with good lighting and a stable surface matters.
What a sharp edge is
A chisel or plane blade is a strip of steel with a flat back on one side and an angled bevel on the other. The two surfaces meet at the cutting edge. Sharpening is the process of making those two surfaces meet cleanly, with no flaws, so the line where they meet is as thin as possible.
A dull edge is simply one where that line has become rounded, nicked or worn. Sharpening removes a little steel until the damaged part is gone and the two surfaces meet properly again.
The general approach
The details vary with the tools and abrasives you choose, but the idea is the same.
- Flatten the back. The flat side matters because it forms half of the edge. Rub it on a coarse abrasive until the area near the edge is flat and evenly scratched. It generally needs doing thoroughly once on a new tool and then only touching up.
- Grind or shape the bevel if needed. If the edge is chipped or the bevel is uneven, use a coarse abrasive to establish a consistent bevel. Do not overheat the steel on a power grinder; if the metal turns blue, the temper may be damaged. Slow, cool grinding and water cooling help.
- Hone on progressively finer abrasives. Work through coarse, medium and fine grits, each removing the scratches left by the last. Keep the angle steady.
- Raise and remove the burr. As you grind the bevel, a thin wire of metal called a burr forms along the back of the edge. Feeling it with a fingertip, moving away from the edge, tells you that you have reached the edge. Then lightly flatten the back on the finest abrasive to remove it.
- Strop. Many people finish by drawing the edge across leather or a similar surface, sometimes charged with fine polishing compound, to remove the last of the burr.
- Test. A chisel should pare thin end grain on a scrap of softwood without crushing it. A plane should produce a fine, continuous shaving.
Choosing abrasives
Several systems work: oil stones, water stones, ceramic stones, diamond plates and abrasive paper stuck to a flat surface. Each has its fans, and none is the only right choice. What matters:
- Flatness. The abrasive must be flat or the edge will not be.
- A range of grits. Coarse removes metal quickly, fine polishes.
- Cleanliness and lubrication. Follow the maker’s instructions on water or oil.
- Cost and maintenance. Some stones need regular flattening, and abrasive sheets need replacing.
For a beginner, a modest set of abrasives on a flat base is enough to produce good results.
Holding the angle
A bevel angle in the neighborhood of 25 degrees is common for bench chisels and plane blades, with steeper angles for tougher work and shallower ones for fine paring, but follow the tool’s design and your own experience. Consistency matters more than the exact number.
Ways to keep the angle steady include:
- A honing guide, a clamp that holds the blade at a set angle. This is a good way to start because it takes the guesswork out.
- Freehand sharpening, where you rock the bevel onto the stone by feel. It is faster once learned but takes practice.
- A secondary micro-bevel, a tiny second angle added at the very tip, which makes frequent touch-ups quicker because you only need to remove a tiny amount of steel.
Plane blades and chisels: small differences
- Chisels are mostly a matter of a flat back and a clean bevel. Check that the edge is square to the sides, as a crooked edge will wander in the cut.
- Plane blades should have an edge that is square or very slightly curved at the corners, so the corners do not leave ridges in the surface. Set the blade so it projects only a tiny amount from the sole, and adjust gradually.
Wear and tear differs, too. A plane blade working through knots or grit dulls faster than one used on clean, clear wood, so a sharpened blade may not stay sharp for long on abrasive material such as reclaimed wood, which may hide dirt, sand or nails; see checks for reclaimed materials.
How often to sharpen
The edge tells you. Signs include needing more force, a rougher surface or crushed fibers, shiny dull spots on the edge, and tear-out you did not have before. Touching up a slightly dull edge on the finest abrasive takes seconds, and doing it often keeps work enjoyable. Waiting until the edge is badly worn means more steel to remove and more time on a coarse abrasive.
Common problems
- Rounding the bevel, caused by rocking the blade while honing. A guide or consistent technique prevents it.
- Not flattening the back, which leaves a weak edge that dulls quickly.
- Skipping grits, which leaves coarse scratches that a fine abrasive cannot remove efficiently.
- Over-heating on a grinder, which can soften steel.
- Leaving the burr, which breaks off and leaves a dull edge.
Putting it to use
Sharpening is a skill best learned slowly, on an inexpensive chisel before a prized plane blade. Allow time, accept that your first edges will not be perfect, and judge by results in the wood. A clean, sharp edge makes the hand tools described in the beginner’s overview of hand tools a pleasure to use, helps you cut tidy wood joints, and tends to leave a surface that needs less sanding.