How do I fix a chipped or badly rounded chisel edge?

How far back to grind, why the whole chip has to go rather than most of it, and the three ways to re-establish a bevel without a grinder.

Difficulty: intermediate
Time: 40 min
Read: 4 min
Safety: caution

Short answer

Grind or file the edge back square until the chip has completely gone — check by looking at the flat you have created under a light, and keep going until it is unbroken across the full width. Then re-establish the primary bevel, hone a secondary bevel, and remove the burr. Stopping while any of the chip remains means the tool goes blunt again immediately at that point.

A chipped edge cannot be honed out. Honing works on the last fraction of a millimetre of steel, and a chip is deeper than that. The only cure is to remove metal back beyond the deepest point of the damage across the full width of the blade, which is a grinding job rather than a sharpening one.

Safety

If you use a bench grinder, wear eye protection and use the tool rest — a chisel snatched out of your hand by a grinding wheel is a serious injury. Grinding also overheats the edge easily: steel that turns blue has been softened permanently and that section must be ground away. Dip in water frequently, or use a coarse diamond plate instead and avoid the risk entirely.

What you'll need

Coarse diamond plate, coarse stone or a bench grinder
Medium and fine stones
Honing guide (optional)
Water for cooling
Marker pen (optional)
Square

Step by step

Assess the damage.Look along the edge under a bright light. A blunt edge shows as a fine bright line; a chip shows as a notch. Note the depth of the deepest notch — that is how far back you have to go, plus a fraction.
Square the edge off first.Hold the chisel vertically against a coarse plate or the side of a grinding wheel and grind the very tip square, straight across, until every trace of the chip has gone. You will end up with a small flat along the edge. That flat is the target, and it must be continuous across the full width.
Check the edge is square to the sides.Use a small square against the side of the blade. An edge ground out of square is a nuisance for the rest of the tool's life, and this is the moment to correct it.
Re-establish the primary bevel.Grind or hone a fresh bevel at around 25 degrees, working back until the flat you created is almost, but not quite, gone. Leaving a hair of the flat means you have not yet reached the edge, which is exactly what you want before switching to the finer stones.
Control the heat if you are grinding.Light pressure, keep the tool moving across the wheel, and dip in water every few seconds. Any blue tint means that part of the steel has lost its hardness and must be ground away entirely. This is the one irreversible mistake in the process.
Consider skipping the grinder.A coarse diamond plate removes steel surprisingly quickly and cannot overheat the tool. It takes longer than a grinder and is entirely safe. For one damaged chisel it is the better choice for most people.
Hone the secondary bevel.Raise the angle slightly, to around 30 degrees, and hone on a medium then a fine stone until a burr forms along the entire width. The burr appearing across the full width is the proof the two surfaces have met everywhere.
Remove the burr.A few strokes with the back flat on the finest stone, then a light pass on the bevel, then a strop. Check for the burr with a thumbnail drawn lightly along the back — nothing should catch.
Test and work out what caused it.The edge should pare end grain cleanly. Then think about the cause: a hidden nail, levering with the chisel, dropping it, hitting a masonry surface, or a bevel angle too low for the work. Fixing the cause matters more than fixing the edge.

Tips

Scribble marker pen on the bevel before grinding. Where the ink is removed shows exactly where the stone or wheel is contacting, which is the fastest way to learn what your hands are doing.
A white aluminium oxide wheel, run slowly, is far kinder to tool steel than the grey wheel supplied with most bench grinders.
It is normal for the first proper regrind of a neglected chisel to take half an hour or more. After that, honing takes a minute.
If a chisel has chipped on a hidden nail, check the rest of the timber with a magnet before continuing.

If it doesn't work

The edge keeps chipping in the same timber

Cause: Bevel angle too low for the work — a paring angle used for chopping, or hardwood and knots — Fix: Hone a steeper secondary bevel, around 30–35 degrees. A steeper edge is less keen and far more durable.

The edge crumbles rather than chips

Cause: Poor steel, or heat damage from an earlier grinding — Fix: Grind back well past the affected section. If it recurs through a good depth of the blade, the chisel is not worth the time.

A rounded edge that will not take a burr

Cause: Repeated freehand honing has rocked the bevel into a convex curve, so the stone never touches the edge itself — Fix: Regrind the primary bevel flat, then use a honing guide until the muscle memory is there.

One corner is lower than the other

Cause: Uneven pressure during honing — Fix: Square the edge off and start again, then use a guide and concentrate pressure on the high side until it evens out.