How to Use a Cut-Off Wheel Safely on Metal and Steel

Check the wheel and grinder first

Most trouble with cut-off wheels starts before the grinder is switched on. Take a minute to check that the wheel and the tool belong together.

Start with size and arbor. The wheels on our comparison page are mostly 4-1/2 in discs with a 7/8 in arbor, which fits the common 4-1/2 in angle grinder. Then check speed. A wheel's max RPM must be at or above the grinder's no-load speed, and both numbers are printed on the tools. Some makers publish the rating, such as 13,300 RPM for the VOISEN 100-pack and 13280 RPM for the Diablo disc. Others do not list it. If you can't find the rating, check the wheel's label or the maker's documentation before using it.

Next, look at the wheel itself. Do not use one that is chipped, cracked, warped or damaged from a drop. Bonded wheels also age and soak up moisture, so store them flat and dry. When in doubt, throw it out. If you are still choosing wheels, our best cut off wheels page lists size, thickness, pack count and listed metals side by side.

• Wheel diameter fits the grinder and its guard
• Arbor size matches (7/8 in for the wheels discussed here)
• Wheel max RPM is equal to or higher than the grinder's speed
• No cracks, chips, bends or damp, crumbly edges
• Wheel type is made for cutting, not grinding

Set up your gear and workspace

A cut-off wheel throws sparks, metal dust and sometimes fragments. Good protection is not optional. One maker's listing reminds buyers to protect eyes, ears, face, hands and body, and that is sound advice.

Keep the guard on the grinder and set it between you and the wheel. Never remove it to reach a tight spot. Clear flammable items such as rags, solvents, sawdust and fuel containers from the area, because sparks travel farther than you expect. Keep a fire extinguisher nearby when working indoors.

Clamp the workpiece firmly. Holding a piece with one hand while cutting with the other is a common way to get hurt. Support both sides of the cut so the piece does not pinch the wheel as it separates.

• Safety glasses plus a full face shield
• Hearing protection, since grinding is loud
• Dust mask or respirator, especially for stainless steel and coated metal
• Leather gloves and long sleeves made of natural fiber
• Sturdy boots and no loose clothing, jewelry or dangling hair

How to make the cut, step by step

The same basic method works on mild steel, stainless, pipe and rebar. The goal is a straight, steady cut with the wheel doing the work.

Unplug a corded grinder, or remove the battery from a cordless one, whenever you change wheels or adjust the guard.

• Mark the cut line and clamp the work so the line is easy to reach.
• Fit the wheel on the 7/8 in arbor, tighten it with the proper flange and wrench, and confirm the wheel sits flat.
• Hold the grinder with both hands and stand to the side, out of the wheel's line of travel.
• Start the grinder away from the metal and let it reach full speed.
• Bring the wheel to the cut at a right angle (90 degrees) to the surface and let it bite lightly.
• Use light, steady pressure. If the grinder bogs down or the wheel glows, ease off.
• Keep the wheel in the same plane. Do not twist it, rock it or try to cut a curve.
• Finish the cut, lift the wheel out, and let it stop spinning before you set the grinder down.

Cutting steel and other metals

Thin wheels remove less metal, so they cut faster and cleaner. On our page, listed thicknesses run from 1 mm to 1.2 mm. For example, the DEWALT DW8062B5 is listed at 1.14 mm, and the Diablo disc at 1.02 mm. Compare thickness only where the maker lists it, since not every product does.

For steel, angle iron, pipe and rebar, a thin bonded wheel is a common pick. The DEWALT listing names carbon steel, stainless steel, nickel alloys, pipe and rebar. Stainless and nickel alloys can work harden and produce more heat, so use steady pressure and avoid dragging the wheel. Always check that the metal you are cutting is on the wheel's listed materials.

Round stock and pipe are easier if you make a shallow groove first, then deepen it as you rotate the piece. Thin sheet can grab and vibrate, so back it with solid support close to the cut.

Bonded wheels or diamond wheels

Both types cut metal, but they wear differently. Bonded abrasive wheels shrink as you use them and are sold in packs. Diamond wheels keep their diameter and use a solid steel body, which makers say lowers shatter risk. Their long cut life numbers are maker claims, not verified results, and they come in small packs, such as two or three per pack on our page.

The EZARC diamond wheel lists dry cutting of metal, rebar, iron, alloy steel, aluminum and pipe. The ONEGOTOOL diamond wheel also names tile and stone. The same safety rules apply to every type, including guard use and protective gear.

Common mistakes to avoid

Most cut-off wheel accidents come from a few habits. Pinching is the big one. If the wheel binds in the cut, the grinder can kick back toward you, so keep the cut open and supported.

Do not start the grinder with the wheel already touching the work, and do not force it. Pressing harder does not speed the cut. It overheats the wheel and raises the risk of breakage.

Do not use a cut-off wheel to grind. These wheels are thin and made to take pressure on the edge, not on the flat face. Side loading can crack or shatter them. If you need to smooth a cut edge or remove weld, switch to a grinding wheel or flap disc made for that job.

Finally, dispose of worn or damaged wheels properly and do not mix up wheels from different grinders or sizes.

Frequently asked questions

Are cut-off wheels directional?

Most flat bonded cut-off wheels are not tied to a spin direction. Some wheels, especially certain diamond blades, may show an arrow on the body. If you see one, mount the wheel so it matches the grinder's rotation, and follow the maker's instructions.

Can you use a cut-off wheel to grind?

No. Cut-off wheels are thin and built for cutting with the edge. Grinding on the flat face puts side load on them and can crack the wheel. Use a grinding wheel or flap disc for smoothing and shaping.

How do I know when to replace a bonded wheel?

Replace it if it is cracked, chipped, warped or has worn down so far that it no longer clears the guard properly. Also replace any wheel that has been dropped or stored damp.

Can I use a smaller wheel on a bigger grinder?

Do not mix sizes. Use the wheel diameter the grinder and guard were made for. Check the grinder's rated speed against the wheel's max RPM, and confirm the arbor fits.