Grinding and cutting safely

May 12, 2009
By: David Smith

Hand-held angle grinders, which now are being used more frequently in industries besides metal fabrication and welding, can cause injury if used improperly and without following all safety guidelines. This article covers the safety practices involved when using these grinders with resin-bonded wheels.

Hand Held Angle Grinders

Hand-held angle grinders have long been used extensively in the metal fabrication and welding industries; however, they also now are being used more frequently in the mechanical contracting, autobody, masonry, and stone-working industries for grinding, cutting, and polishing. This expanded usage speaks to the versatility of angle grinders, which can accommodate a range of accessories, such as resin-bonded grinding and cutting wheels; diamond wheels for cutting and surface grinding; abrasive disks; flap disks; wire brushes; nonwoven abrasives; and even diamond coring bits. Nonetheless, the most common applications involve grinding and cutting with resin-bonded wheels.

The old adage "accidents can happen" applies to grinding and cutting just as it does to most aspects of our daily activities, whether it be walking down a flight of stairs or driving our cars. Safety practices that must be followed to minimize accidents and maximize safety when using angle grinders and resin-bonded wheels apply to the wheels, the grinder, and the operator.

The Wheel

The most common resin-bonded wheels are Type 27 (depressed center) for grinding and cutting and Type 1 (flat) for cutting. Although these wheels are strong, they are not immune to breakage. Should a wheel break apart in use, pieces of the wheel could strike and injure you or a co-worker. To help minimize this risk:

  1. Never grind with a wheel that is designed exclusively for cutting. Such a wheel is not constructed to withstand the side pressure exerted when grinding.
  2. Always visually inspect the wheel for possible damage before mounting it on the grinder. If in doubt, don't use it.
  3. Don't use a wheel if it has nicks, cracks, or if it has been dropped.
  4. Allow newly mounted wheels to run at full no-load speed on the grinder (with guard in place) for at least one minute before beginning to grind or cut.
  5. Never exceed the maximum RPM rating indicated on the wheel. For example, a 4 -in. wheel rated at 9,000 RPM should not be used on a 4 -in. grinder with a no-load speed of 10,000 RPM (typical for a 4 -in. grinder). Many people remain under the impression that it is the loadoperating speed that cannot be exceeded. This is simply not the case. Expanding on this point, a 4 -in. grinder without speed stabilization electronics and a no-load speed of 10,000 RPM will have an operating speed of about 6,500 RPM when you put the wheel under pressure against the work. It is not the 6,500 RPM that applies; it is the 10,000 RPM no-load RPM that is critical.
  6. The wheel must be affixed to the grinder with the correct mounting flanges. Using improper flanges can impart damaging stress to the wheel. For the same reason, do not tighten the outer mounting flange/nut excessively.
  7. Never force a wheel onto the grinder or alter the size of its mounting hole.
  8. Do not grind on the side of the wheel.
  9. Never jam the wheel into the work.

The Grinder

To use the grinder safely:

  1. Always use the proper, correctly positioned wheel guard. Never use the grinder without a guard. The guard should be adjusted so that the least amount of wheel is exposed toward you. Many grinders have wheel guards that do not require tools for adjusting, which means adjustments generally can be made quickly and easily.
  2. Never use a grinder if its no-load speed (RPM) is unknown.
  3. Never use a wheel larger than that for which the grinder is designed, e.g., a 7-in.-diameter wheel on a 6-in. grinder.
  4. Don't use the grinder without a side handle. Use both hands. Neveroperate a grinder in a one-handed manner; should the wheel jam, it would be almost impossible to maintain control of the grinder, even if it were equipped with a slip clutch.
  5. Position the power cord clear of the spinning wheel.
  6. Never lay the grinder down until the wheel has come to a complete stop. (Grinders with electric or mechanical brakes minimize the waiting time.)
  7. Be sure the switch properly turns the grinder on and off. If not, do not use the tool until necessary repairs are made.
  8. Ensure that the grinder is unplugged before mounting or removing a wheel.
  9. Read the instruction manual supplied with the grinder before use. (Unfortunately, this basic step is very often ignored.)

The Operator

  1. Wear gloves and safety glasses or protective face shields. As appropriate, wear a dust mask, hearing protection, and a workshop apron capable of stopping small abrasive or workpiece particles.
  2. Do not wear loose-fitting clothing or jewelry, and keep hair away from moving parts.
  3. Do not overreach. Maintain proper footing and balance at all times.
  4. Position yourself to the side of the grinder opposite the wheel and wheel guard.
  5. Ensure bystanders are a safe distance away from your work area.
  6. Always maintain a firm grip on the tool, and position your body and arms to resist kickback forces should the wheel jam.
  7. Take care to work only with accessories designed for the grinder you are using.
  8. Never run the grinder while carrying it at your side.
  9. Do not expose the tool to rain or wet conditions. Water entering a power tool increases the risk of electric shock.
  10. Do not abuse the power cord. Never use the cord for carrying, pulling, or unplugging the power tool.

These guidelines cover some of the more important aspects of grinding and cutting safety using resin-bonded wheels, but this is not an exhaustive list. For further information, refer to the American National Standard titled "Safety Requirements for the Use, Care and Protection of Abrasive Wheels," ANSI B7.1-2000. Copies are available form the American National Standards Institute ( and the Unified Abrasives Manufacturers' Association (UAMA). Other useful publications on grinder and wheel safety are available from UAMA (

David Smith

Contributing Writer
Metabo Corp.
1231 Wilson Drive.
West Chester, PA 19380
Phone: 610-436-5900