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A hollow grind removes steel across the middle of the bevel and leaves a concave face, so the chisel only touches the sharpening stone at the edge and the heel. A flat grind keeps the entire bevel in contact with the stone. The hollow grind is faster to refresh and easier to hold at a consistent angle; the flat grind puts more steel directly behind the cutting edge and holds up better to chopping and mortising. The right answer depends on how you sharpen, what you cut, and how much time you want to spend at the bench.
What the two grinds actually are
Both profiles start with the same primary bevel angle — usually 25° for a bench chisel, sometimes 30° for a mortise chisel or a chisel you strike with a mallet. The difference is the shape of that bevel face.
On a hollow grind, the bevel is ground on the curved face of a grinding wheel. The wheel’s radius produces a concave arc, so the bevel is a shallow valley between the cutting edge and the heel. On a flat grind, the bevel is a plane — either ground on a flat platen or, more commonly in a home shop, worked flat on a diamond plate or water stone.
Most chisels arrive from the factory with a flat or very slightly hollow bevel. The hollow is something you introduce deliberately when you set up a grinder, not something you get by default.
Head-to-head comparison
The table below compares the two profiles on the things that actually affect your work. Numbers are typical for a 1-inch bench chisel with a 25° primary bevel.
| Factor | Hollow grind | Flat grind |
|---|---|---|
| Bevel shape | Concave arc, typically 6–8 in. radius on an 8-in. wheel | Straight plane from edge to heel |
| Steel behind the edge at 25° | Thin — the arc removes material just behind the edge | Full bevel thickness — more mass directly behind the edge |
| Time to re-hone after dulling | About 30–60 seconds on a fine stone; only the edge and heel contact | About 2–4 minutes; the whole bevel must be worked |
| Time to re-establish a damaged edge | Fast on a grinder — under a minute per chisel if the wheel is dressed | Slow by hand; needs coarse stone or grinder anyway |
| Honing angle control | Easier — the two contact points act as a built-in angle guide | Harder — the whole bevel must stay flat on the stone |
| Edge durability in chopping | Good for paring and light chopping; can chip if the bevel is thin | Better for mortising, heavy chopping and hardwoods |
| Typical setup cost | Requires a bench grinder ($80–$200) plus a white or CBN wheel ($40–$120) | Requires only stones you probably already own |
| Risk of overheating the edge | Real — a dry wheel can blue a thin edge in seconds | None on water stones; low on diamond plates |
Why the hollow grind is faster — and where it bites you
The hollow grind’s advantage is mechanical. Because the bevel is concave, the chisel contacts the stone at only two places: the cutting edge and the heel. That means less steel to remove when you hone, and the two contact points naturally stabilize the chisel at the correct angle. Most people find a hollow-ground chisel easier to keep flat on a water stone than a flat-ground one, because the bevel doesn’t rock.
The trade-off is steel behind the edge. A 25° hollow grind on an 8-inch wheel leaves a thinner cross-section right behind the edge than a 25° flat grind does. For paring — where the cut is controlled and the force is low — that’s an advantage, because a thinner edge slices more easily. For chopping, mortising, or working dense hardwoods like white oak or hickory, that thin section is where chips start.
The other cost is heat. A dry bench grinder can raise the temperature of a thin edge past the point where the temper is affected in a couple of seconds. The fix is a light touch, a freshly dressed wheel, and quenching in water every pass or two. If you see a straw or blue color on the bevel, you’ve gone too far and the steel needs to be ground back past the discoloration.
Why the flat grind is more durable — and where it bites you
A flat grind leaves the full bevel thickness directly behind the edge. On a 25° bevel that’s more steel supporting the cutting edge, which is why mortise chisels and heavy chopping chisels are usually flat-ground. The edge resists chipping and takes more mallet blows before it needs attention.
The cost is sharpening time. To re-hone a flat-ground bevel you have to work the entire face on the stone, and any rocking or tilting rounds the bevel. Keeping the whole bevel in contact takes practice, and a honing guide helps. If you sharpen freehand, a flat bevel will show a slightly convex or rounded profile after a few sessions unless you’re disciplined about keeping the chisel flat.
Flat grinding also has no grinder requirement. A 1000-grit diamond plate and a 6000-grit water stone will maintain a flat bevel indefinitely, and the setup cost is whatever stones you already own. For a small garage shop where floor space and budget are tight, that matters. If you’re still working out where the sharpening station goes, the layout advice in How to Lay Out a Workshop in Ten Feet is worth reading before you buy a grinder.
The most common mistake: grinding a hollow bevel on a chisel you plan to chop with
The single most common mistake in this comparison is hollow-grinding a chisel that will be struck with a mallet. A 25° hollow grind on a 1-inch bench chisel is fine for paring and light work. Put that same chisel into a mortise in white oak and the thin steel behind the edge will chip or fold, and you’ll spend more time at the grinder than you saved. The fix is straightforward: either raise the bevel angle to 30° on chopping chisels, or keep a flat grind on the chisels that see mallet work and reserve the hollow grind for paring chisels.
A related mistake is over-grinding. People see a hollow and keep grinding to make it deeper, thinning the edge further. A shallow hollow — a millimeter or two of concavity — is enough to get the honing benefit. You don’t need a deep scoop.
Finally, the hollow grind doesn’t fix a dull edge by itself. If the back of the chisel isn’t flat, no bevel geometry will give you a clean cut. Flattening the back is the first job on any new or flea-market chisel, and it’s the same discipline that makes a hand plane work — see How to Tune a Hand Plane Sole Flat for the same principle applied to a plane sole.
Choosing for your shop
If you already own a bench grinder and a white or CBN wheel, hollow grinding is the faster path for paring chisels and bench chisels used for light work. If you don’t own a grinder, or your chisels see mallet work in hardwoods, a flat grind on stones is the lower-risk choice and costs nothing beyond what you already have.
A practical middle ground many woodworkers use: hollow-grind the primary bevel at 25° on a grinder, then hone a small flat micro-bevel at 27–30° at the edge on a stone. The hollow keeps re-honing fast, and the micro-bevel adds durability where it matters. It’s a compromise, not a purity test — pick the one that keeps your chisels sharp and your work moving. If your joinery decisions are already shaped by a small shop, the same pragmatic thinking applies in How to Choose Joinery for a Small Garage Shop.
Decision checklist
- Will this chisel ever be struck with a mallet? If yes, lean flat grind or use a 30° bevel.
- Do you own a bench grinder and a white or CBN wheel? If no, flat grind on stones is the practical choice.
- Is the chisel for paring and light work? Hollow grind is faster to maintain and slices more freely.
- Are you working dense hardwoods like white oak or hickory? Favor more steel behind the edge.
- Can you keep a bevel flat on a stone freehand? If not, a hollow grind is more forgiving.
- Do you want the fastest re-hone between cuts? Hollow grind, with a small micro-bevel for durability.
Frequently asked questions
Does a hollow grind make a chisel sharper than a flat grind?
Not sharper in absolute terms — both can be taken to the same fine grit and both will shave. The hollow grind is easier to keep at a consistent angle, which in practice means it stays sharp longer between sessions. The flat grind has more steel behind the edge, which helps it hold up to chopping.
Can I hollow-grind a chisel on a slow-speed grinder?
Yes, and a slow-speed grinder (often around 1,750 rpm) is actually the safer choice because it heats the edge more slowly than a high-speed grinder. Use a white or CBN wheel, dress it regularly, and quench the chisel in water every pass or two to avoid softening the steel.
What angle should I use for a hollow grind on a bench chisel?
25° is the standard primary bevel for a bench chisel used for paring and light work. If the chisel will be struck with a mallet or used in hardwoods, go to 30°. A common compromise is a 25° hollow grind with a small 27–30° micro-bevel honed at the edge.
How do I know if I've overheated the edge while grinding?
Watch the color of the steel. Straw or blue discoloration means the temper has been affected and the edge will be soft there. Grind back past the discoloration until you see clean steel, then re-hone. Quenching in water every pass or two prevents most of this.
Is a flat grind better for mortise chisels?
Generally yes. Mortise chisels take repeated mallet blows in dense wood, and the extra steel behind a flat-ground bevel resists chipping better than a thin hollow-ground edge. If you do hollow-grind a mortise chisel, use a 30° bevel rather than 25°.