One of the most popular tools in any metalworking shop is the right-angle hand grinder. Its versatility covers the gamut from blending weld beads to mold and die repair.
Norton Company (Worcester, Massachusetts) has introduced a new abrasive disc and back-up pad that will extend the usefulness of right-angle grinders even farther. For the first time, says the company, an operator can actually see what the grinder is doing in the cut.
In a typical grind with a round disc, an operator must frequently pull the grinder away from the workpiece surface to inspect what's been done. Many operators use a right-angle grinder at a 45-degree angle (basically cutting on the outer edge of the wheel) to facilitate this grind-some, inspect-some cycle. Often the grind itself shows evidence of this stopping and starting.
Norton's system is called AVOS which means "allows view of the surface." AVOS products, which are an abrasive disc of various grit sizes and a back-up pad, are manufactured with a unique triangular-shaped silhouette.
Three holes in the disc and back-up pad (one on each lobe of the triangle) align so that when they rotate on a right- angle grinder, the operator can see through the disc and actually watch the grind in process.
Seeing the grind through the rotating holes encourages the operator to use the grinder at a more productive 10- to 15- degree angle of attack on the workpiece. At the shallower angle, more grinding disc surface is in the cut which increases metal removal rates.
While the holes allow the operator to see the grind, they serve another important role. As the disc rotates, the holes allow for a "rest time"a brief period when no cutting takes place on the workpiece surface.
During this period, an air flow caused by a scoop design molded into holes in the back-up pad pulls loose abrasive and swarf out of the grinding zone. Clearing the cut zone reduces heat and friction by 25 percent in tests conducted by Norton. The result is longer life for the grinding disc and a reduction of burn on the workpiece.
The triangle shape of the disc and back-up pad also function to clear the cut of swarf and grit. A wiping action takes place as each lobe enters the cut zone. Material is expelled by this action.
It may appear that a triangular shape like the AVOS would cause "bounce" or vibration in the cut. Actually there is none, says the company. The back-up disc is designed to flex in a way that off-sets any vibration caused by the shape. It cuts like a round disc.
At the 10- to 15-degree angle of attack recommended for this system, the lobes of the triangle flex as each enter the zone. As each lobe exits, it relaxes. This flexing action acts as a preload on the abrasive disc and actually creates a mechanical advantage which reduces the amount of pressure needed by the operator.
To reduce the possibility of snagging the holes in the grinding disc on sharp corners or other protrusions, the circumference of each hole is compressed slightly in the manufacturing process. The edge of the hole rides slightly below the disc surface and tends to over ride irregularities in a surface. In a demonstration of how this works in operation, an AVOS disc ground a nail flush with no apparent degeneration of the disc surface.
Currently the AVOS product is available in fiber discs, SG abrasive, zirconia alumina and aluminum oxide in grit sizes from 24 to 120. For rust removal and polishing applications Norton's Beartex material is available for AVOS.