Abrasive flap wheels are often used for deburring, stress relief, and fine grinding to reach dimensional tolerances. They use grains of abrasive grit material adhered to a backing of paper, plastic or cloth, and formed upon a central core to form a starburst-shape that is used along the circumference of the wheel. The action of a flap wheel is much like a car wheel; the flap wheel rotates along the central axis, like the axle in a car, but acts on the circumference of the wheel, like an automobile wheel drives upon the pavement. Flap wheels are used with tools such as vertical shaft grinders and right-angle grinders.
When selecting a flap wheel, consider the grit material type. For example, aluminum oxide is the most common abrasive material, chosen because it is durable and compatible with many different materials. Each grit material has different attributes, like brittleness, toughness, and hardness. Tough grit materials like ceramic aluminum oxide last longer than grit material such as aluminum oxide. Ceramic aluminum oxide is often used for medium-to-high material removal on metals.
The next consideration is grit size. With a lower grit size like 40, there are fewer and larger grains in a given area, making it "coarse" and commonly chosen for removing excess material and shaping a workpiece. With a high grit size like 400, there are more and smaller grains in a given area, making it "fine" and creating a smooth surface finish.
Another important factor is how the wheel is constructed. Flap wheels are coated, meaning an adhesive is used to attach the abrasive grains to a backing.
Lastly, consider the fastening type, which indicates how the flap wheel attaches to the tool. There are various fastening types, such as metal hub quick-change, plastic snap quick-change, threaded, and adhesive-backed. A standard fastening type refers to a single hole, called an arbor hole, in the center of the wheel.