All About Angle Grinders

An angle grinder is a metalworker's best friend. It not only can transform ugly welds into smooth, paintable surfaces but also can cut metal stock, remove rust and deburr pipe (as well as perform a bunch of home-improvement chores outside the realm of metalworking).

Of course, the key to making the best use of this tool is to understand it and the many attachments available to expand its versatility. Here's a brief primer to help you get started.

Angle grinder anatomy
An angle grinder is a fairly simple tool that includes a motor-driven spindle onto which a cutting wheel or some other task-specific implement is attached.

Angle grinders can be powered by compressed air or gasoline, but most are electric, powered by standard 110-volt household current.

Unlike drills, which typically spin at 700 to 1,200 rpm, angle grinders spin at a very high speed — often in excess of 10,000 rpm. To avoid injury, it's vital that you follow a few basic safety guidelines whenever you work with an angle grinder:

  • Wear a face shield, hearing protection, long sleeves and gloves.
  • Unplug the grinder when you're changing wheels.
  • Attach the auxiliary handle, and maintain a firm grip with both hands.
  • Allow the tool to reach full speed before touching it to the workpiece.
  • Work at a consistent speed. Do not force the cut, but do not work so slowly that the tool burns the workpiece.
  • Use the guard whenever possible.
  • Run a new wheel in a protected area for one minute to make sure it's not defective before using it on a workpiece.
  • Orient the work so debris is directed downward and so that the wheel spins away from, not into, any sharp edges. Sharp edges can catch on wheels (especially wire brushes) and cause the grinder to kick back.
  • Keep bystanders away. Everyone in the vicinity should wear safety glasses.
  • Keep sparks away from flammable materials.
  • Never use a dust-collection attachment when cutting metal.
  • Do not use lubricants with cutoff wheels. Use lubricants only with grinding wheels when specified by the manufacturer.

Wheels and attachments
To use an angle grinder to its full potential, you'll need to understand the various wheels and attachments that are available:

Cutoff and grinding wheels
When outfitted with a cutoff or grinding wheel, an angle grinder can make quick work of cutting metal and smoothing welds. Technically speaking, cutoff and grinding wheels are referred to as "bonded abrasives" because abrasive material is combined with a resin or vitreous binder and then heat-formed into a solid wheel or disc (as opposed to a coated abrasive such as sandpaper, which consists of abrasive material that's applied to a backing). The only difference between the two is thickness. At 3/32 to 1/8 in. thick, cutoff wheels are thinner than their grinding counterparts, which can range from 1/4 in. to 1 in. thick. Cutting and grinding wheels for angle grinders come in a variety of profiles (see drawing below).

Cutting wheels can easily be distinguished from grinding wheels by their thickness — cutting wheels are much thinner than those used for grinding.

The most common are a solid disc (Type 1) and a depressed-center disc (usually designated as Type 27, but also Type 28 or Type 29). The only real difference between Type 1 and Type 27 wheels is that the spindle nut that secures the wheel is recessed in the depressed area on a Type 27 or 28 wheel, allowing you to grind on flat surfaces. High-quality cutting and grinding wheels use a mixture of aluminum oxide and zirconia oxide along with reinforced layers of mesh that improve cutting life. But if you plan to use a cutting or grinding wheel on stainless steel or other high-nickel alloys, be sure the wheel is sulfur- and chloride-free to prevent contamination of the workpiece.

Wheel profiles

The most common profiles for bonded-abrasive cutting and grinding wheels are a flat wheel (Type 1) and a depressed-center wheel (Type 27, 28).

Wire wheels and brushes
When it comes to removing paint or rust, nothing beats a wire wheel. Wire cup brushes work best for stripping paint or rust from broad, flat areas, whereas flat wire wheels fit into crevices and corners more easily. When purchasing a wire wheel or brush, make sure to match its threads to the spindle threads on your grinder. Most angle grinders have 5/8-in. spindle threads, but there are a few oddballs.

Wire wheels and brushes such as the wire disc and the cup brush shown here are commonly used to remove paint and rust from metal surfaces.

Flap discs
For removing material (including weld grinding, blending and deburring), a flap disc may be your best choice, as it both grinds and finishes in one step. Aluminum-oxide flap discs are suitable for most general-purpose applications and are less expensive, but zirconiaoxide discs remove stock quicker and last longer. For the best performance, look for flap discs that are manufactured from ceramic grains, as they provide the most aggressive grinding yet operate cooler and faster than other materials. Ceramic is specifically recommended when working with high-alloy steels, titanium, nickel alloys and all extremely hard materials.

Specialty discs
A number of newer abrasive products specifically tailored for cleaning and finishing have been adapted for use on the grinder. Clean-and-strip discs strip metal without removing material and are a safer alternative to wire brushes when removing paint and adhesives, cleaning weld seams and removing welding scale and discoloration. Surface-conditioning discs are composed of open nylon webbing impregnated with abrasive grains. Because they are flexible, they allow for polishing contoured surfaces, removing gasket material, cleaning weld spatter and removing heat discoloration.

Typical wheel-changing procedure requires you to lock the spindle and then use a wrench (included with the grinder) to loosen the arbor nut.

Beyond metalworking
When you get tired of crafting metal pieces, you can find an entire realm of other uses for angle grinders. From cutting concrete, mortar, stucco, pavers, brick and tile to shaping stone and granite, an angle grinder outfitted with the right attachment can serve as more than a utilitarian implement; it can be an artistic tool. Browse the aisles of your local home-improvement or hardware store to see the many different cutting, polishing and abrading wheels that are available beyond those for metalworking, and you'll start to see just how far this tool can take you. Your imagination may be the only limit to what an angle grinder can help you accomplish.