How to choose a flap disc: grit, abrasive and maximum speed

To choose a flap disc, look at three things: the grit, the abrasive and the maximum speed. Grit 40 is for roughing and removing welds and rust, 80-120 for finishing, and 220 for a fine finish. Zirconia and ceramic remove more material and last longer than aluminium oxide (corundum), which is enough for occasional use. The maximum speed marked on the disc must not be lower than that of your machine: in the collection it ranges from about 8,500 to 26,000 rpm.

The types

• Flap disc for angle grinders: the classic type with overlapping cloth flaps, in diameters from 115 to 180 mm with a 22 mm bore. There are models with angled flaps, such as the DeWalt DT3265-QZ, DT3266-QZ and DT3267-QZ, with the rim tilted relative to the plane of the disc.
• Mounted flap wheels: they fit in the collet of a straight grinder or a drill, for working inside cavities, corners and shaped surfaces. One example is the Fervi mounted aluminium oxide cloth flap wheel.
• Mounted combination wheels in cloth and abrasive felt: they combine cloth and felt to smooth and give a more even finish, like the Fervi RGM060/30F, the RGM060/30M and the RGM060/30VF.
• Micro wheels and mini discs: small-diameter (even 30 and 50 mm) for precision work, like the Fervi micro flap wheels. They run at much higher speeds.
• Soft and curved discs: shapes and backings designed to conform to irregular surfaces: read the product data sheet for the intended use.

How to choose by job

The features to look at

• Grit: in the collection it runs from 36 to 220. A low number means coarse grit and an aggressive cut; a high number means fine grit and a smoother finish. As a rule you start with a coarse grit and move on to a fine one.
• Abrasive material: zirconia and ceramic are the most durable, corundum is the most common and economical, silicon carbide is used on hard, brittle materials, and nylon (non-woven) is for cleaning and satin finishing.
• Diameter and bore: 115, 125, 165, 180 and 200 mm for angle grinder discs, 30 to 75 mm for the smaller wheels. The bore of the discs is 22 mm. It must match the flange.
• Maximum speed: every disc has its own limit. Values found include 13,300, 12,250 and 8,500 rpm for angle grinder discs (the larger the disc, the lower the limit) and 25,000-26,000 for small mounted wheels.
• Backing: fibreglass (stiffer, for roughing) or nylon (more flexible).
• Pack: 1, 10 or 25 pieces. For daily use it pays to keep a stock.

Common mistakes

• Not checking the maximum speed: the disc must be able to spin at least at the speed of the machine.
• Pressing too hard. A flap disc works with light pressure and a slight angle, and this way it neither overheats nor marks the workpiece.
• Starting with a grit that is too fine and wearing out the disc without removing material.
• Using the same disc on steel and on aluminium: aluminium clogs the abrasive.
• Carrying on using the disc when the cloth is worn down to the backing.

Frequently asked questions

What grit do I need to remove rust and paint?

A 40-60 grit removes material quickly; then you move on to 80-120 to even out the surface.

Zirconia, ceramic or corundum: which should I choose?

For daily work on steel, zirconia or ceramic are better, as they last longer. For occasional use corundum is enough.

Is a flap disc suitable for wood?

Yes, the collection is designed for metal and wood. Use medium or fine grit and light pressure, because coarse grit leaves marks.

Can I fit a mounted wheel on a drill?

Yes, if the shank fits in the chuck and you respect the maximum speed of the wheel. The smaller wheels need a very fast machine, such as a straight grinder.

You can find all the models in the flap discs for metal and wood collection: ask for a quote or advice from the AMES technicians, stating the material to be worked, the machine and the grit.