What to Know About Using a Bench Grinder
Updated: Apr. 18, 2023
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 it 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.
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 bench 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.
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.
Make Tool Sharpening Guides
Here’s a better way to hold tools securely while you’re grinding them—and take the guesswork out of creating the right bevel angle. It’s a short piece of 2×4 with an angled end and a 1-1/4-in. hole for a clamp. I made one for sharpening chisels and plane blades, and a few more with different angles for wood-turning tools. Large labels with the tool’s name tell you which blocks are for which tools. For a Delta grinder with a 6-in.-diameter wheel, a 5-1/2-in.-long piece of 2×4 aligns the tool to the wheel just right. For other bench grinders, you may need to adjust this length. Note: The angle you cut on the block is not the same as the tool’s bevel angle. But let’s skip the math. To determine the block angle, turn off the grinder and hold the tool’s bevel flush against the wheel. The angle of the tool shaft to the workbench is the angle to cut on the 2×4. Our thanks to Ray Caputo for this sharp accessory.
Consider a Low-Speed Grinder for Sharpening
Unless they’re variable speed, most bench grinders run at about 3,450 rpm. If you’re careful and keep the wheel dressed (more on that in another tip), these high-speed grinders work fine. But for sharpening garden and other tools, a low-speed grinder running at 1,750 rpm is a better choice. The lower speed reduces the chance you’ll overheat the edge of your tool. Another advantage of a low-speed grinder ($100 to $150) is that this type typically includes friable white grinder wheels, which do a better job of sharpening than the gray grinder wheels usually included with high-speed grinders. See how to use an angle grinder.
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 bench 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.
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.
Make an Angle Gauge
Chisels and other cutting tools work best if their edges are ground at the correct angle. You can search online to find the optimal angle for whatever tool you’re sharpening. Most wood chisels should be ground to about a 25-degree angle with a secondary micro-bevel angle of 30 degrees on the tip of the blade. An angle gauge allows you to set the tool rest at the desired angle. You can make an angle gauge from a thin piece of cardboard using an inexpensive protractor. 1. MARK THE ANGLE ON CARDBOARD Align the center mark on the protractor with the top edge of the cardboard. Then turn the protractor until the desired angle is also aligned with the top edge. Draw a line along the protractor to mark the angle. Don’t forget to label the angle. Cut along the line to create the gauge. 2. ADJUST THE TOOL REST Set the cardboard on the tool rest and adjust the angle of the tool rest until the wheel contacts the center of the angled portion of the cardboard gauge.
Upgrade the Tool Rest
Inexpensive bench grinders have tool rests that are finicky and difficult to adjust. If you do a lot of tool sharpening or simply want a bench grinder tool rest that’s easier to adjust, consider adding a stand-alone tool rest. There are several variations, some made for specific tasks like sharpening lathe turning tools. This Veritas model has two adjustments for positioning and aligning the tool rest, and levers for easy tightening. You can also buy an attachment that holds chisels or plane irons.
Make Your Grinder Portable
Even the most nicely organized home 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.
Easy-to-Clamp Mobile Base
Shazam! Fasten your bench-top tools to your workbench in seconds. Bolt 3/4-in. plywood bases on the tools and then glue and screw a wood strip along the front edge to fit into a woodworking vise. Crank this strip into a vise to lock the tool into place. If you don’t have a vise, drill a couple of clearance holes along the face of the wood strip on the base and drive screws through the strip into the edge of your workbench. Then just unscrew to remove the tool.
Set Up a Polishing Station
A bench grinder fitted with a wire wheel on one side and a cotton buffing wheel 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.
Sharpen Your Lawn Mower Blade
Sharpening your lawn mower blade is easy with a bench grinder. Grind the tapered cutting edges with a grinder only if you see nicks in the blade. Follow the factory angle of the cutting edge. The grinder will remove nicks in the blade much faster than you can file them.
Grinder Safety
- Wear safety glasses with side shields, goggles or a face shield when grinding.
- Turn the grinder on and stand aside until the wheels come to full speed. If there’s a problem, you won’t be in the path of flying debris.
- Inspect grinder wheels for cracks or damage. Before you install a new wheel, suspend it by a screwdriver through the center hole. Tap the wheel lightly with the plastic handle of another screwdriver. The wheel should ring. If you hear a dull thud instead, the wheel is probably cracked and should not be used.
- When you install a wheel, don’t overtighten the nut. Just snug it up. Overtightening could crack the wheel.
- Keep the shrouds and spark shields in place. And maintain a 1/8-in. or less gap between the tool rest and the grinding wheel.
Not All Grinding Wheels are the Same
You can use two kinds of aluminum-oxide wheels to sharpen your chisels; one is blue-gray and the other white. We used the darker-color wheel, which is harder and will keep its shape longer. The drawback, however, is that it grinds hotter than the softer, white wheel. Too much heat will weaken the steel. The soft wheel will need more frequent shaping with a dressing tool, but you’ll be less likely to burn the edge of your chisel while grinding. For best results, use a 100-grit wheel to shape your chisel blades.
Know When to Replace a Wheel
Slide the wheel over your finger and tap the wheel in four places with a screwdriver handle. All taps should sound the same. If they don’t, scrap the wheel. It’s cracked.
