Spinning your wheels?

Separate grinding wheel facts from myths

Practical Welding Today May/June 2003
May 29, 2003
By: Roger Cloutier

Grinding wheels used in welding and fabrication are strong, tough tools, but many in the industry have called them "rocks" or "stones," implying that they're unbreakable.

Grinding wheels

Grinding wheels, rocks, stones—what's the difference?

Grinding wheels used in welding and fabrication are strong, tough tools, but many in the industry have called them "rocks" or "stones," implying that they're unbreakable. This myth, or misconception, has led people to become complacent, ignoring manufacturer, industry, and government requirements for their safe use.

The first fact to know about grinding wheels is that if they're used improperly, they can break, causing serious injury or death.

Safe operation depends largely on how you treat your grinding wheel while you use it. It's your responsibility to follow all safety precautions in the storage, handling, and use of a grinding wheel to keep potentially dangerous occurrences to a minimum. The fact is, grinding wheels—when used improperly—can break, causing serious injury or death.

Let's review some common misconceptions and the facts about grinding wheels.

Wheel Storage and Handling

Myth No. 1:Grinding wheels are so tough that they can't sustain enough damage to cause them to break during transportation and handling.

Fact:While grinding wheels can be strong and well-packaged, they can be damaged during handling and transportation. This can cause a grinding wheel to break.

Inspect all incoming grinding wheel containers. If you see any damage to the container, don't accept the shipment. Never ship or accept a grinding wheel that isn't in a package.

Always use care when handling grinding wheels to prevent damage. Wheels never should be dropped or allowed to bump into an object.

Myth No. 2:Once the grinding wheel is mounted on a machine, improper storage no longer is a problem.

Fact:Workplace grinding wheel storage is important. Many wheel breakages and injuries can occur from unsafe machine and wheel storage.

Don't store grinding wheels on portable machines. During the work shift, store grinders and wheels on special racks or hooks designed to protect them from accidental damage caused by, for example, being pulled off a worktable onto the floor.

When a grinding wheel isn't on its machine, store and protect it properly. Store wheels in original packages or in other enclosures designed to protect the grinding wheels from accidental bumping.

Myth No. 3:Grinding wheels are so tough that they can be stored in any weather condition.

Fact:Store grinding wheels to avoid such hazards as:

  • Exposure to water.
  • Any temperature or humidity conditions that cause condensation on the wheel.
  • Freezing temperatures.

Myth No. 4:Grinding wheels can be stored forever.

Fact:You should use grinding wheels within two years of their manufacture date. Always rotate grinding wheel stock so that the oldest grinding wheel is used first.

Wheel Selection and Inspection

Myth No. 1:Grinding wheels that have been chipped, or notched, and damaged are safe and cut better than wheels without such damage.

Fact:The act of mounting and using a damaged grinding wheel is dangerous and can cause accidents.

Grinding wheels can become damaged during shipping, so it's important to inspect the wheel visually for cracks or other signs of damage before mounting the wheel.

Never use a wheel that is chipped, cracked, gouged, has any sign of damage, or that you suspect might be damaged.

Myth No. 2:Many portable grinding and sanding machines and grinding wheels are on the market, and they all are safe to use as long as you can get the grinding wheel on the machine.

Fact:Failure to select the proper grinding wheel for the machine you're using is a major cause of grinding wheel breakage and injury.

Never mount a grinding wheel on an air sander or any machine that isn't designed and guarded specifically for that grinding wheel. Personal injury and death can occur when a grinding wheel is mounted on the wrong machine.

Make sure the wheel is the correct type for the machine and your application. For example, thin type 27 wheels that are 1/8 inch thick are designed for notching, root pass grinding, and shallow cutoff operations in which the machine and wheel are held at a 90-degree angle to the workpiece.

Thicker type 27 wheels, which are 1/4 in. thick, are designed for side grinding when held at a shallow 30-degree angle to the workpiece and not flat to the material being ground.

Mounting the Wheel

Myth No. 1:An improperly mounted grinding wheel can't cause an accident.

Fact:Improperly mounting a grinding wheel can cause wheel failures and personal injury.

Mounting grinding wheels on table saws, radial arm saws, milling machines, sanders, electric motors, routers, or any other machine not specifically designed, guarded, and approved for grinding wheels can result in serious injury and even death. Some common reasons operators remove a grinding wheel guard on a portable machine are to:

  1. Reduce the machine's weight.
  2. Allow the machine inside tight areas.
  3. Increase visibility during grinding.
  4. Grind at a shallow or improper angle (that is, flat).
  5. Mount a large grinding wheel on a small machine.

All of these excuses are factors that can lead to potential disasters.

Myth No. 2:Portable grinders don't require maintenance, and they pose little danger if they aren't maintained properly.

Fact:Failure to maintain and inspect portable grinders properly can result in machine failures, such as grinding wheel overspeed, bent mounting spindles, distorted flanges, worn spindle bearings, and damaged guards. These maintenance problems can lead to wheel breakages, serious injuries, and death.

Portable air-driven grinders require air regulators that you must maintain and set for the manufacturer's recommended air pressure for the tool being used.

Don't be fooled: Machine maintenance is critical to your safety. Inspect all portable grinders, including speed measurements, in accordance with American National Standards Institute (ANSI), Occupational Safety and Health Administration (OSHA), and the machine manufacturer's instructions. Never inspect the speed of a grinder while a wheel is mounted.

You can prevent accidents with proper air control and machine maintenance.

Myth No. 3:All grinding wheels are speed-tested at 1.5 times the maximum operating speed marked on the grinding wheel, so it's OK to overspeed the grinding wheel as long as the wheel's speed doesn't exceed its rated speed by a factor of 1.5 times.

Fact:Testing requirements vary from product to product, manufacturer to manufacturer; therefore, not all grinding wheels are speed-tested.

More important, the speed test is designed to simulate the stresses applied to a grinding wheel during normal operation. Stresses during grinding don't occur singularly and aren't independent of each other. The combination of normal grinding stresses and excessive centrifugal force caused by overspeed can break even the strongest wheel.

Never overspeed a grinding wheel. Always compare the speed of the grinder with the speed marked on the wheel or package to make sure the machine's speed is at or below the rated speed of the grinding wheel. Overspeeding a grinding wheel is another major cause of wheel breakage and personal injury.

Myth No. 4:All portable grinding wheels are mounted the same way.

Fact:Flanges drive and support the grinding wheel and must have sufficient contact area. They must be the proper type and size for the grinding wheel being mounted on the machine.

Type 1 wheels used for applications such as cutting off and inline grinding require flanges that are matched, relieved with equal bearing surfaces, flat, and free of foreign particles. If flanges aren't uniform in diameter and contact area, they can create cross-bending stresses when tightened, which can cause the wheel to break. In addition to flanges that aren't uniform, worn and distorted or warped flanges can cause the grinding wheel to slip or break.

Grinding wheel flanges for straight wheels must be at least one-third of the grinding wheel's diameter, with the exception of cutoff wheels, which must be one-fourth the cutoff wheel's diameter.

Flanges used with portable cup wheels, such as types 6 and 11, must be flat and not relieved, because a relieved flange can pull the mount bushing out of the wheel. Flanges used to mount types 1, 6, and 11 wheels must be checked for flatness of the wheel's flanges with a straight edge. A straight edge placed on the bearing surface of a flange must not rock. You can check it with a feeler gauge for a more exact measurement.

Myth No. 5:Mounting a cup wheel against a large hex nut is safe and will make wheel removal easy.

Fact:The hex nut or the back of a spindle won't support a cup wheel. Grinding occurs on the wheel's rim, and without a proper flange, the wheel may break.

Depressed-center wheels—types 27, 28, and 29—that are larger than 5 in. in diameter require specially designed adapters—a large back flange and nut—because of their shape and use.


The adapter, or back flange, should extend beyond the central hub, or raised portion, and contact the wheel to counteract the side pressure on the wheel in use. The adapter nut, which is less than the minimum one-third diameter of the wheel, fits in the depressed side of the wheel to prevent interference in side grinding.

Starting and Using the Wheel

Myth No. 1:As long as you have a wheel guard on the machine, you are safe.

Fact:For a grinding wheel guard to be effective, it must be:

  • The correct type: cup guard for cup wheels, flat guard for flat wheels.
  • Properly adjusted between the operator and the grinding wheel.
  • Set at the correct height.
  • Unaltered: Never cut a wheel guard.

Myth No. 2:Because the grinding wheel has been inspected and mounted properly on a guarded machine, it's ready to grind.

Fact:To ensure that the grinding wheel hasn't been damaged during storage or transportation, run the wheel for one full minute with the guard in place and in an enclosed area, such as a steel drum or under a workbench.

Be sure that no one is standing in front of, or in line with, the wheel. If the wheel was damaged in handling or storage, it most likely will break within the first full minute of rotation at operating speed.

Myth No. 3:Personal protective equipment (PPE) is uncomfortable and isn't necessary.

Fact:PPE saves eyes, fingers, teeth, and limbs. Always wear appropriate PPE—such as eye and face protection, aprons, arm guards, and gloves—for your specific application.

Myth No. 4:Grinding wheels are unbreakable.

Fact:Grinding wheels break when they're snagged, jammed, or bumped into the workpiece. Discard the wheel if any of these situations occur.


Myth No. 1:All grinding wheel injuries involve a broken grinding machine or wheel. Dust will not harm you or cause you any ill effects.

Fact:Inhaling dust generated during grinding can impair your breathing.

Most of the dust generated during grinding is from the material being ground. Before grinding begins, review the Material Safety Data Sheet (MSDS) for the material being ground, the grinding wheel, and all other products used in the process.

Grinding may generate hazardous dust, fumes, or vapor. Exposure to airborne concentrations may result in eye, skin, and respiratory tract irritation.

Always use adequate ventilation, dust controls, PPE, and all other appropriate equipment and procedures for grinding. Owners and users share responsibility for determining the suitability of a product for a particular use. Check all applicable industry, federal, state, and local regulations, and read all warnings carefully before using grinding wheels.

Roger Cloutier

Senior Product Safety Engineer
Saint-Gobain Abrasives Inc.
One New Bond St.
P.O. Box 15008, M.S. 301-411
Worcester, MA 01615-0008
Phone: 508-795-5000

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Practical Welding Today was created to fill a void in the industry for hands-on information, real-world applications, and down-to-earth advice for welders. No other welding magazine fills the need for this kind of practical information.

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