As a type of rotating tool used on a grinder, Flap Wheels are used for sanding and are made from strips (i.e., flaps) of abradant radiating from a center hub. A flap wheel’s outside diameter may range from 4″ to more than 24″.The basic components of a flap wheel are the center hub of the wheel and the abrasive used for the wheel.
The hub defines the arbor of the wheel at its center. The flaps are secured to the hub by various methods. The usual method is adhesive or glue that bonds the flaps together and to the hub. Types of hubs that can be used for Flap Wheels are the cardboard core hub, the metal-centered hub, and the heavy-duty mechanical hub.
Abrasive flaps, whether woven and nonwoven, are much more common as material for flap wheels than other materials like cardboard, buff cloth, felt, or neoprene, though all these other materials also have their own specific uses in a flap wheel. Flap wheel abrasives are crystals and are grouped into the natural or artificial categories. The natural abrasives include diamond and quartz, whereas the major forms of artificial or manufactured abrasives are silicon carbide (SiC or carborundum) and aluminum oxide.
Silicon carbide, which is 9.5 on the Mohs scale of hardness, is a fused crystalline abrasive with a tendency to fracture under pressure. This tendency enables it to present new sharp edges to a work piece, making SiC fast-cutting and well suited to ferrous metals. Like SiC, aluminum oxide is a fused, hard crystalline abrasive too (9.0 on the Mohs scale); however, it is difficult to fracture and inclined to slowly dull.
Choosing the correct flap wheel will depend on (1) the machine you use, (2) the rpm rating of the drive spindle, and (3) the arbor size. Flap wheels do not have the backup support that abrasive belts do, so the normal rules for selecting grain type and grit do not apply. On soft or hard materials, the aluminum oxide grain type is used, while SiC gives a mirror finish on aluminum and stainless.
Using flap wheels can produce a finish that is about two grades finer than that produced by an abrasive belt. For improved roughing, 80 grit or rougher may be recommended. Referring to a flap wheel parameter table can also be a good idea.
Mounted flap wheels are obtainable in diameters like 1″, 1 1/2″, 2″, 2 1/2″, and 3″. Such wheels are mounted on a 1/4″ spindle, to fit 1/4″ tools. The unmounted type is available in diameters such as 4″ and 6″.
