An angle grinder is a handheld power tool that uses a spinning disc to cut, grind, polish, or sand hard materials like metal, stone, and concrete. It’s one of the most versatile tools in any workshop, capable of doing the work of several single-purpose tools depending on which disc you attach. The name comes from its defining feature: a gear assembly inside the head that redirects the motor’s rotation 90 degrees, so the disc spins perpendicular to the body of the tool rather than in line with it.
How an Angle Grinder Works
The motor inside the grinder’s body spins a shaft that connects to a small gear assembly in the tool’s head. That gear assembly turns the motor’s output 90 degrees to an output spindle, where you mount a disc or wheel. This right-angle design is what gives the tool its compact shape and makes it easy to hold against a flat surface, press into a tight corner, or cut downward into material.
You control the tool with a rear grip (which usually houses the trigger or switch) and a side handle that bolts onto the gear head. The side handle can typically be repositioned for left-handed or right-handed use. A semicircular guard sits over one half of the disc to deflect sparks and debris away from you, and a spindle lock button lets you hold the shaft still while you swap discs by hand or with a wrench.
Common Sizes
Angle grinders are categorized by the diameter of disc they accept. In the United States, disc sizes range from 4 inches up to 12 inches, but the most popular sizes for general use are 4.5 and 5 inches. Outside North America, equivalent sizes are labeled as 115 mm and 125 mm. Larger grinders (7 and 9 inches) are heavier, more powerful tools used for deep cuts in concrete or large-scale metalwork. For most home and shop tasks, a 4.5-inch grinder is the standard starting point.
Disc size and motor power increase together. A small grinder might draw 6 or 7 amps, while a 9-inch model can pull 15 amps or more. No-load speeds (how fast the disc spins with nothing pressing against it) vary too, and this matters for safety: every disc is rated for a maximum RPM, and using a disc on a grinder that spins faster than the disc’s rating can cause it to shatter. A grinding disc rated for 6,650 RPM mounted on a grinder spinning at 8,500 RPM, for example, exceeds the disc’s limit by 22 percent. Always check that your disc’s RPM rating meets or exceeds the grinder’s speed.
Types of Discs and What They Do
The disc you mount determines what the grinder can do. Swapping discs takes under a minute, which is why a single angle grinder can replace so many other tools.
- Grinding wheels are the default. They have a thick, rigid profile and a ribbed edge designed to remove material quickly. Use them to smooth rough metal edges, clean up welds, or reshape steel.
- Cut-off wheels are thin discs (sometimes just 1 mm thick) made for slicing through metal, rebar, or bolts. They cut fast but wear down and should be replaced frequently.
- Flap discs are layered with overlapping strips of sandpaper. They work like aggressive sandpaper on metal, removing burrs, smoothing sharp corners, and blending scratches. They offer more control than a grinding wheel and leave a finer finish.
- Diamond discs have a coating of abrasive diamond particles on their edge. They’re built for cutting extremely hard materials like concrete, tile, brick, and dense stone. They cost more than other discs but handle jobs no standard abrasive wheel can.
- Wire cup brushes have steel bristles pointing forward from a cup-shaped base. They strip rust, old paint, and scale from metal surfaces. Wire wheels (where the bristles point outward) do similar work but reach different angles.
- Sanding and polishing pads attach with hook-and-loop or adhesive backing and let you use the grinder for finish work, from smoothing wood to buffing metal to a shine.
Power Sources: Corded, Cordless, and Pneumatic
Corded electric grinders are the most common type for home users and small shops. They deliver consistent power as long as you have an outlet, and they’re the least expensive option. The tradeoff is a cord that limits your range and can become a tripping hazard, and motors that can overheat under sustained heavy use.
Cordless (battery-powered) grinders have become increasingly capable as lithium-ion battery technology has improved. They’re ideal for jobs where you’re moving around a site or working somewhere without power. Run time depends on the battery and how hard you’re pushing the tool, but for intermittent cuts and grinding, a single charge handles most tasks. They tend to cost more upfront because of the battery and charger.
Pneumatic (air-powered) grinders run off a compressor and are the standard in heavy industrial settings. They’re roughly 30 percent lighter than electric equivalents, don’t overheat (the motor simply stalls if overloaded instead of burning out), and can be used safely in wet conditions or explosive environments where electric tools pose a risk. Their lifespan is longer too, often 7 to 15 years with regular oiling. The downside is you need a compressor, which makes them impractical for most home users.
What You Can Do With One
The most common use is metalwork: grinding down welds, cutting steel stock to length, cleaning rust off surfaces, and smoothing sharp edges on fabricated parts. If you’ve ever watched someone work on a car frame, a railing, or a gate, an angle grinder was almost certainly involved.
In construction, angle grinders fitted with diamond blades cut concrete, brick, and tile. They score pavers, trim stone, and open up slots in masonry walls for electrical conduit. With a sanding or polishing pad, the same tool can smooth a concrete countertop or polish a granite edge. With a wire brush, it strips old finishes from metal furniture, fences, or machinery before repainting. This range is what makes the angle grinder one of the most widely used power tools in both professional trades and home workshops.
Safety Hazards and How to Manage Them
Angle grinders spin at thousands of RPM and throw off hot sparks, metal fragments, and dust. OSHA identifies the primary hazards as high-speed flying particles, kickback, dust and fume inhalation, noise, cuts, and electrical shock. Kickback, where the spinning disc catches on the material and jerks the tool violently, is the most dangerous because it can send the grinder into your body or throw the workpiece.
Essential protective gear includes safety glasses or a full face shield, hearing protection, leather gloves, and natural-fiber clothing (synthetic fabrics can melt from sparks). A dust mask or respirator is important when cutting concrete, stone, or anything that produces fine particles. Always keep the guard in place and adjusted so it sits between you and the disc.
Modern grinders include several built-in safety features that are worth looking for when buying. Electronic clutch protection reduces kickback by sensing when a disc jams and cutting power to the motor. Brake technology can stop a thin cutting wheel in under one second and most other discs in under two seconds, which limits how long the disc keeps spinning after you release the trigger. Paddle switches shut the grinder off the moment you let go. Anti-restart protection prevents the motor from starting if a battery is inserted while the switch is locked in the on position. These features don’t replace careful technique, but they significantly reduce the consequences of something going wrong.