How To Use a Bench Grinder

Even if you don't use a bench grinder every day, you're going to want to know your way around the tool. Learn some great tips here.

sharpening the tip of a screw on a bench grinder
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Master Your Bench Grinder

A bench grinder is probably not a tool you’ll use every day. However, if it’s available and set up correctly, you’ll be surprised how often one comes in handy for everything from sharpening tools to rounding over thread ends on a cutoff bolt. We’ve assembled these tips to help you get the most out of your grinder.

a close up of the wheel of a bench grinder
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Match the Wheel to the Job

Most bench grinders come with one coarse- and one medium-grit aluminum oxide grinding wheel. These are fine for everyday grinding on steel. But there are better wheels for special tasks like sharpening tools or grinding aluminum, copper, brass or stone. Here are a few key points to remember when choosing wheels.

  • Grits go from coarse to fine, which are indicated by numbers like 80 grit or 220 grit, with larger numbers indicating finer grits.
  • Coarse grits cut fast but leave a more ragged edge.
  • Fine grits cut slower and leave a more polished surface.
  • For tool sharpening, look for“friable” aluminum oxide wheels. Friable means that the grit breaks off easily as you grind to constantly expose fresh grit. This keeps the metal cooler. Friable wheels are usually white.
  • For most sharpening tasks, a 60-grit and a 120-grit wheel are a good combination.
  • Don’t grind soft metal or stone on aluminum oxide wheels. To grind these materials, look for a silicon carbide wheel.

dipping a chisel into water to cool it after grinding
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Keep a Container of Water Handy

Most chisels and other cutting tools are made of tempered steel. If the steel gets too hot and turns bluish black, it’s overheated and won’t hold an edge very long. To avoid ruining the edge of a tool by overheating, keep water nearby to cool the tool. A good technique is to move the tool once across the grinder for no more than a few seconds. Then dip it in the water. If the steel edge does overheat and turns color, grind the edge back to good steel and start over.

grinding a small screw using a locking pair of pliers
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Grind Small Objects Safely

Hold small objects with locking pliers. This keeps your fingers a safe distance from the grinding wheel and protects them against burns from the hot metal. It also gives you better control over the grinding process.

dressing the wheel of a grinder
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Dress Wheels Frequently

Wheel dressing squares the face of the wheel, but more important, it exposes new grit for more efficient cutting. As a wheel is used, the spaces between the cutting grit can become clogged, and the grit itself dulled. A wheel in this condition can cause overheating and slows material removal. A wheel dresser like the one shown here ($15 to $30) has a bar with diamond grit impregnated in it. Holding the bar against the spinning wheel cuts away the surface to expose new grit, squares the face of the wheel and rounds the wheel.

To use a dressing tool like this, start the grinder and wait for it to reach full speed. Then press the diamond wheel dresser against the spinning wheel, holding it perpendicular to the face of the wheel. Be sure to wear a good-quality dust mask. The fine aluminum oxide dust is very bad for your lungs. Draw a pencil line on the wheel before you start to help you gauge when you’ve removed enough material from the wheel. Dress the wheel just until the pencil line disappears.

a chisel sparking against a spinning grinder wheel
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Watch For the Sparks to Come Over the Top

When you’re sharpening a chisel or other tool, you can tell when the edge is getting sharp by watching the sparks. When the edge is blunt, the sparks are deflected downward. But as the edge gets sharper, the sparks roll over the tool and cascade down the surface facing you. When you see this start to happen, be careful about grinding much more because a thin edge is very vulnerable to overheating.

a grinder that is a little bit portable
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Make Your Grinder Portable

Many workshops don’t have enough bench space to devote a section to a bench grinder. A good solution is to mount your grinder to a board or small stand so you can clamp it to the bench when you need it, and store on the shelf when you don’t. The compartment on this grinder stand is a good spot to keep your dressing tool and safety glasses so they’re handy when you need them. For a fancier version, build a little drawer to fit the space under the grinder.

The stand is built from two 12 x 16-in. pieces of 3/4-in. plywood separated by two 4 x 12-in. uprights. We used two 5/16-in. bolts with washers and nuts to attach the grinder, leaving enough space in front of the grinder to mount a stand-alone tool rest.

using a special polishing wheel on a bench grinder
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Set Up a Polishing Station

A bench grinder fitted with a wire wheel ($15) on one side and a cotton buffing wheel ($8) on the other side, or buffing wheels on both sides, makes a great cleaning and polishing tool. You’ll also need a set of polishing compound sticks ($14). Polishing compound sticks are color coded to indicate the grit, from coarse to very fine.

To use the polishing wheel, hold the stick against the buffing wheel as it spins to transfer some polishing compound to the wheel. Then hold the object lightly against the wheel and let the compound polish the surface.