How to sharpen a knife on a bench grinder

You can sharpen a knife on a bench grinder, but the gray stones it came with are the wrong tool. They run at about 3,450 RPM at 36 and 60 grit, which is right for a mower blade and far too hot for a knife edge. Fit a paper sharpening wheel (or a fine wheel) and a polishing wheel, keep the wheel turning off the edge, use the lightest pressure that cuts, and cool the blade in water every pass or two. If that sounds like a lot of setup, a belt sharpener does the same job more safely.

Should you use a bench grinder at all?

For axes, machetes and old garden knives, yes. For a good kitchen knife, we'd use something else. The problem is speed and heat: a dry 6-inch wheel turning at 3,450 RPM, like the stock wheel on WEN's 4276, removes steel quickly and puts the heat into the thinnest part of the blade. Hunker's tool writer goes further and says neither a bench grinder nor an angle grinder is the right way to sharpen kitchen knives. Our advice: practice on cheap knives first, and keep thin, hard Japanese blades away from any dry wheel.

If you do want to use the grinder, the wheel you fit matters more than anything else on this page.

Which wheel to fit

Paper wheels are the classic bench-grinder knife setup. The Razor Sharp 8-inch Deluxe Kit has an abrasive wheel, a slotted polishing wheel, extra silicon carbide grit, rouge and conditioning wax, and its listing says the wheels work best above 3,000 RPM on a 5- or 6-inch grinder. The Keen Edge WKS600 kit is the 6-inch version: a sharpening wheel, a slotted honing wheel, 220-grit silicon carbide powder, white rouge and a lubricant, rated to 4,200 RPM. For a final strop, a 6.5-inch leather honing wheel fits 1/2, 5/8 and 3/4-inch arbors.

One serious catch. An 8-inch paper wheel won't fit inside a 6-inch grinder's guards, and Woodcraft's listing for the Razor Sharp kit says to remove them. That conflicts with the grinder maker's manual: WEN's says to always use the guards, spark deflectors and eye shields, and that accessories it doesn't list aren't recommended. We don't recommend running a grinder with its guards off. If a kit asks you to remove them, that choice and its risk are yours alone, so read your own grinder's manual before you decide. For most knives, the belt sharpener further down is the safer way to get the same edge.

Safety, from the grinder manual

These come from WEN's manual for its 4276 6-inch bench grinder, which is typical of the class. Read your own grinder's manual too.

• Wear safety goggles that meet ANSI Z87.1, and hearing protection for long sessions.
• No loose clothing, neckties or jewelry, and tie back long hair.
• Bolt the grinder down so it can't tip or walk.
• Keep the wheel guards and eye shields on. WEN's manual says to always use them.
• Inspect each wheel for cracks or missing pieces before use. Replacement wheels must be rated above the grinder's no-load speed (3,450 RPM on the 4276).
• Stand beside the grinder when you switch it on, not in front of it, and let it reach full speed. Never start it with the work touching the wheel.
• Keep the tool rest no more than 1/8 inch from the wheel, and reset it as the wheel wears.
• Grind only on the face of the wheel, never the side.
• Ease the work onto the wheel with light pressure, especially on a cold wheel.
• Keep water away from the grinder itself. WEN says water must never contact it, so the dunk bucket goes on the bench, not under the wheel.
• The wheels take about three minutes to coast to a stop. Don't touch them.

Which way the wheel should turn

Benchmark Abrasives' rule is the right one: the wheel should turn away from the edge. If it runs into the edge, it can catch the steel and pull the knife out of your hand. On a standard grinder the top of the wheel moves toward you, so a paper wheel is used on top, with the knife's edge facing you and the spine toward the motor.

On the front face of a stone wheel, the surface moves downward past the tool rest. Edge trailing there means the edge pointing down. Some jigs hold the knife edge up instead, which can work because the jig controls the angle. Freehand, stick to edge trailing.

Step by step with paper wheels

This is the method the paper-wheel kits describe. It assumes the wheels fit your grinder with its guards in place. If your kit only works with the guards removed, that conflicts with your grinder maker's manual, so don't use it that way; the belt sharpener below is the safer route to the same edge. Either way, keep your goggles on and follow every item on the safety list.

1. Mount the grit wheel and the slotted polishing wheel with the grinder's guards back in place. Charge the grit wheel with wax and silicon carbide, and the slotted wheel with rouge.
2. Color the edge with a marker (the Sharpie trick) so you can see where the wheel is cutting.
3. Set a container of water on the bench within reach.
4. Switch on, standing to the side, and let the grinder reach full speed.
5. Hold the knife at its sharpening angle, about 15 to 20 degrees per side for most Western knives. Our angle chart lists yours. Lay the heel on top of the grit wheel, edge toward you, and draw the knife across so the wheel touches heel to tip in one pass. WEN's manual describes the same direction: work from the heavy end of the blade toward the tip.
6. Raise the handle as the curve near the tip reaches the wheel. Lift off before the tip runs past, or it gets rounded.
7. Dip the blade in water. Do it every pass or two, before it feels warm.
8. Repeat until the marker is gone to the edge and you can feel a burr along the whole length on the other side. Then do the other side the same number of passes.
9. Move to the slotted rouge wheel and make light alternating passes, edge trailing, until the burr is gone.
10. Test on a sheet of paper. A finish on a hand strop takes off anything left.

Heat: the reason grinders ruin knives

A hardened blade keeps its hardness only as long as it stays below the temperature its maker tempered it at. The apex is the thinnest steel on the blade, so a few seconds on a fast dry wheel can push it past that point while the spine is still cool in your hand.

You can see it after the fact. Steel takes on a thin oxide color as it heats: light straw is usually charted at around 400°F, and Hunker's guide puts blue at above about 600°F. Both mean the steel at the edge has softened and will dull quickly. The exact numbers depend on the steel, so treat any color at all as too hot.

• Use the lightest pressure that cuts. More pressure adds heat faster than speed.
• Keep the blade moving. Never dwell on one spot.
• Dip on a schedule, every pass or two, not when it feels hot.
• Use a fine paper wheel rather than the stock stone. The coarse stone removes far more steel per second.
• If you see color, grind back past the discolored strip at the original angle before you finish. Hunker gives the same fix.

Water doesn't undo the damage. It only prevents it, which is why dipping late is the same as not dipping.

The Dremel version

A rotary tool with a small grinding stone can touch up a blade, and plenty of people try it on pocket knives and serrations. Dremel's page for its 932 aluminum oxide stone lists 20,000 to 30,000 RPM for metal, which is several times a bench grinder's speed on a much smaller stone. That makes heat and a wavy bevel very easy. If you use one, clamp the knife, run the tool at its lowest speed, make quick light passes, and dip constantly. For serrations, a tapered diamond rod does a better job for less money; see the serrated knife sharpener picks. A Dremel is a reasonable tool for lawn mower blades.

Knives that shouldn't go near a grinder

• Thin, hard Japanese kitchen knives. They overheat and chip easily. A whetstone is the right tool.
• Any knife you can't replace, until you've practiced on cheap ones.
• Serrated bread knives on a flat wheel. The wheel only grinds down the points.
• Scissors, freehand. WEN's manual says to take them apart and grind only the outside bevel, heavy end toward the tip, which is a job for a jig or a slow wheel.

When to stop and use something else

A powered belt sharpener is the bench grinder done right for knives. The Work Sharp MK2 has a two-speed motor, flexible belts that follow the blade, and an edge guide that supports the knife to the tip. The Work Sharp Ken Onion Mk2 adds a guide adjustable from 15 to 30 degrees and variable belt speed, so you can run it slowly for finishing. Our MK2 vs Ken Onion comparison covers which to buy, and is Work Sharp a good knife sharpener covers how they hold up.

If you already own a 1x30 belt sander, the method in knife sharpening on a belt sander is easier to control than a grinder. And if you like the idea of a wheel but not the heat, a slow wet grinder like the KFMK 10-inch wet sharpening system turns at 90 to 160 RPM in a water trough, with a leather strop wheel and an angle guide. It can't overheat an edge, and the trade is time.

Keep the bench grinder for what it's best at: axes and hatchets, mower blades and reshaping a broken tip before you sharpen by hand.

Sources: WEN, 4276 6-inch bench grinder manual; Benchmark Abrasives, How to Use a Grinding Wheel to Sharpen Knives; Hunker, Bench Grinder or Angle Grinder and Why Your Bench Grinder Turns Tool Edges Blue; Dremel, 932 Aluminum Oxide Grinding Stone; Woodcraft, Razor Sharp Edgemaking System listing. Product details from Amazon listings, checked October 15, 2026. How we research · Affiliate disclosure