Safety and health newsletter for the Oregon construction industry

 

August 14, 2012

grinder wheel with measuring tape

Tool box talk: Abrasive wheel grinders

Abrasive wheel grinders come in many styles, sizes, and designs. Typical bench and pedestal grinders often have two abrasive wheels, or one abrasive wheel and one special-purpose wheel such as a wire brush, a buffing wheel, or a sandstone wheel.

These grinders come with a safety guard covering most of the wheel, including the spindle end, nut, and flange projection. The guards must be strong enough to withstand the effects of a shattered wheel. A work rest and transparent shields are often included.

High speed hazards

Grinders operate at very high speeds – the wheels often rotate at several thousand rpms. If a grinding wheel shatters while in use, the fragments can travel more than 300 mph, so there’s a risk for serious injury from flying fragments and the rotating wheel assemblies (including the flange, spindle end, and nut).

Staying safe

Abrasive wheels used on bench and pedestal grinders must be equipped with safety guards. The safety guard encloses most of the wheel — covering the flange, spindle end, and nut projection — while allowing maximum exposure of the wheel periphery. The exposed surface of the wheel should not exceed 90 degrees or one-fourth of the periphery.

Because the safety guard is designed to restrain the pieces of a shattered grinding wheel, the distance between the safety guard and the opening at the top of the wheel must not be more than 1⁄4-inch. If the distance is greater than 1⁄4-inch, then an adjustable “tongue guard” must be installed to protect workers from flying fragments if the wheel shatters. The tongue guard must be adjusted to maintain a maximum 1⁄4-inch distance between it and the wheel.

An adjustable work rest must also be installed and adjusted to maintain a maximum clearance of 1⁄8-inch between it and the wheel. This prevents the operator’s hands or the work from being jammed between the wheel and the rest.

All abrasive wheels must be inspected and “ring-tested” before they are mounted to ensure that they are free from cracks or other defects. Wheels should be tapped gently with a light, nonmetallic instrument. A stable and undamaged wheel will give a clear metallic tone or “ring.” It’s a good idea for the operator to stand to the side of the machine when powering it on in case a crack or defect was not detected when the wheel was inspected.

The spindle speed of the machine must also be checked before mounting the wheel to be certain that it does not exceed the maximum operating speed marked on the wheel.

Abrasive wheels used on bench and pedestal grinders must be equipped with safety guards. If the distance between the safety guard and the opening at the top of the wheel is greater than 1⁄4-inch, then an adjustable “tongue guard” to protect workers must be installed.

Adjustable work rests must also be installed and adjusted to maintain a maximum clearance of 1⁄8-inch between it and the wheel.

Tongue guard exceeds 1/4-inch from grinder wheel
Tongue guard exceeds 1/4-inch from grinder wheel.
Tongue guard is missing on this grinder
Tongue guard is missing on this grinder.
No tongue guard and the work rest exceeds 1/8-inch from grinder wheel
No tongue guard and the work rest exceeds 1/8-inch from grinder wheel.
 

Click images for full size pictures

 

Feel free to copy this newsletter | About This Newsletter | Contact Us