What is a flap disc?
A flap disc is an abrasive disc for an angle grinder made of overlapping flaps of abrasive cloth glued in a fan pattern around a backing plate. As you work, the flaps wear away layer by layer and expose fresh grit. That lets one disc both remove material and leave a smooth finish.
Types
- Flat (Type 27). The flaps lie almost parallel to the backing. Use at a shallow angle of about 5-15 degrees for flat surfaces and an even finish.
- Conical (Type 29). The flaps are angled, with a working angle of about 15-25 degrees. More aggressive, good for welds and edges.
- Grit. Coarse (40) for heavy stock removal and weld beads, medium (60-80) for general work, fine (120) for finishing. A lower number means a coarser grit.
- Grain. Zirconia and ceramic grains suit steel and stainless steel; aluminium oxide is the cheaper all-rounder and also works on timber.
| Flat (Type 27) | Flaps almost parallel to the backing; use at a shallow angle of about 5-15 degrees for flat surfaces and an even finish. |
|---|---|
| Conical (Type 29) | Angled flaps with a working angle of about 15-25 degrees; more aggressive, good for welds and edges. |
Application
- Pick the right disc. On stainless steel, use a disc marked as suitable for stainless (inox, iron-free) and never one that has been used on mild steel. Iron particles left behind will rust on the stainless surface.
- Check the speed rating. The maximum speed is printed on the disc and must be at least the no-load speed of the grinder. A typical 125 mm (5 in) disc is rated to 80 m/s, which is 12,200 rpm.
- Always fit the guard. Never remove it to get a better view.
- Wear PPE. Safety glasses or a face shield, hearing protection, gloves and a dust mask when dust builds up.
- Let the disc do the work. Too much pressure glazes the flaps and discolours the metal. Keep the disc moving.
- Timber. It removes wood quickly but also leaves deep scratches and burn marks easily. Use a fine grit and light pressure.
Common mistake: running the disc down to the backing plate. Replace it before the flaps are gone.
Related terms
- Sander
- Welding
- Welding on
- Stainless steel
- Corten steel
- Welding hammer
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