What Are Grinding Wheels Used For and What Are They Made Of?

What a grinding wheel is

A grinding wheel is a wheel made of abrasive grains held together in a bond. People also call it an abrasive wheel, a grinder wheel, a grinding disc or a grinding stone. Which name you hear often depends on the tool. Discs for angle grinders are usually called grinding discs, while the thicker wheels on a bench grinder are called bench wheels.

Each grain acts like a tiny cutting edge. As the wheel spins, thousands of grains scrape away small bits of material. When a grain dulls, it should break away or wear down so fresh, sharp grain is exposed. That is why a wheel gradually wears smaller as you use it.

What grinding wheels are used for

Grinding wheels do far more than make sparks. The common jobs fall into a few groups, and the job tells you which wheel type to look for.

• Removing material fast, such as taking down welds or leveling a rough edge.
• Cleaning surfaces, such as removing rust, mill scale, paint, glue or epoxy coatings.
• Shaping metal, such as profiling edges or blending a joint.
• Sharpening tools, such as drill bits, chisels, knives and blades.
• Grinding concrete, stone and tile, such as smoothing a slab or removing thinset.

What grinding wheels are made of

Every wheel has three basic parts: abrasive grain, a bond that holds the grain together, and sometimes reinforcement. The grain does the cutting. The bond sets how fast the grain is released as it wears. Reinforcement helps a thin wheel hold together under stress.

Aluminum oxide is the usual abrasive for steel. Silicon carbide suits non-ferrous metals and tool sharpening. Diamond is used on concrete, stone and coatings, and it is not meant for general metal grinding. On our comparison, the HOMO FABER disc uses aluminum oxide with fiberglass reinforcement, while the POLIWELL bench wheel uses silicon carbide.

Common bonds include resinoid (resin), rubber and vitrified (a fired, glass-like bond). Resin-bonded discs are common for angle grinders. Many thin discs also have layers of fiberglass mesh inside. The DEWALT DW4523, for example, is listed as fiberglass reinforced.

Abrasive types compared

This table summarizes how the three common abrasives are typically used, along with examples from the products on our comparison page.

Shapes, grit and size

Wheel shape matters. A depressed center (Type 27) disc is built for angle grinders and has a raised center so the mounting nut sits clear of the work. Cup wheels are shaped like a bowl and are common for concrete and stone. Straight bench wheels mount on a bench grinder.

Grit is the coarseness of the grain. Lower numbers cut coarser and remove material faster. Higher numbers cut finer. On our comparison page, listed grits run from 36 to 400. A 46 grit disc suits weld and rust removal, while a 150 grit wheel suits tool sharpening.

Size must match your tool. A 4.5 in angle grinder needs a 4.5 in wheel, and the arbor hole must fit the spindle. Arbor sizes among the products we compare include 0.875 in, 0.625 in and 0.5 in. Never force a wheel that does not fit.

Safety basics

Grinding throws sparks and debris, and a damaged wheel can break apart at speed. Treat the wheel label as a firm limit.

• Check the maximum RPM on the wheel. Your grinder must not exceed it. Ratings among the models we list run from 3600 RPM on an 8 in bench wheel to 13300 RPM on a 4.5 in angle wheel.
• Never use a bench wheel on an angle grinder, or the reverse.
• Inspect each wheel before mounting. Do not use one that is cracked, chipped or has been dropped.
• Wear eye or face protection, hearing protection, gloves and a dust mask. Concrete and stone dust can harm your lungs.
• Keep the guard in place, and unplug a corded tool or remove the battery before changing a wheel.
• Use wet-rated diamond wheels wet only if the label says wet use is allowed, and keep water away from electrical connections.

How to choose the right wheel

Start with your tool, then your material, then the job. Match the diameter, arbor hole and speed rating first. Next pick the abrasive, and finally the grit and pack size.

If you want to see these numbers side by side, our best grinding wheels page lists diameter, arbor size, grit and RPM for several products. Check the abrasive before you trust a high ranking, because three of the ranked products are diamond wheels made for concrete and stone, not metal.

For general steel work with an angle grinder, a 46 grit aluminum oxide Type 27 disc is a sensible starting point. If you grind often, pack sizes in our data range from 1 to 50 pieces. You can also read more about grinding wheel options if you are deciding between bench and angle grinder wheels.

Frequently asked questions

Is a grinding wheel the same as a cutting wheel?

No. Grinding wheels are thicker and built to remove material with the face or edge. Cutting wheels are thin and built to slice through metal. Do not swap one for the other.

How do I know when to replace a grinding wheel?

Replace it if it is cracked, chipped, warped or worn down to the minimum size marked on the label. A wheel that stops cutting and only glazes or burns the work may also be worn out.

Can I use a diamond wheel on steel?

Diamond wheels are made for concrete, stone and coatings, not general metal grinding. For steel, choose an aluminum oxide wheel rated for your grinder.

Does a lower grit number mean a rougher cut?

Yes. A lower number means coarser grain and faster material removal. A higher number leaves a finer finish.