Cut-off wheels

Following the ISO 525 designation, the first letter is the abrasive (A for aluminium oxide, C for silicon carbide), the number is the grit, the next letter is the bond grade, and BF means fibre-reinforced resin bond. Thin cut-off wheels are almost always reinforced resin bond because they must withstand side loads. The label also shows the maximum speed and an expiry date.

Thin wheels of about 1.0 to 1.6 mm cut fast with less heat and burr, suiting sheet, tube and stainless. Thicker 2.0 to 3.0 mm wheels are stiffer and tolerate pressure and vibration, suiting solid bar and heavy sections. The thinner the wheel, the more sensitive it is to twisting in the cut.

Yes. Resin bonds absorb moisture and age, so many manufacturers print an expiry date on the metal ring at the bore, commonly about three years from manufacture. Store them dry, flat and away from heat, and use first in, first out. Expired or damp wheels should be discarded.

No. Type 41 and Type 42 cut-off wheels are designed for radial load through the edge; side grinding can crack and burst the wheel. For combined cutting and light grinding, use a product specifically marked as a combination cut and grind wheel. Always keep the guard fitted and wear eyewear with a face shield.

Type 41 is flat, while Type 42 has a depressed centre that keeps the flange and nut below the disc face, useful when cutting close to a surface. Both need the correct guard for the tool. Common bores for angle grinders are 16 mm and 22.23 mm and must match the tool's flange.

The wheel must fit the machine spindle exactly, commonly 22.23 mm on angle grinders and 25.4 mm or 32 mm on chop saws, with no improvised reducing rings. The wheel diameter must not exceed what the guard is designed for. Fitting a larger wheel usually means removing the guard, which leaves no protection if the wheel breaks.

Keep the wheel square to the workpiece, let it cut with moderate feed pressure and do not rock or twist it in the kerf. Clamp the workpiece so the kerf does not close and pinch the wheel. A pinched or twisted wheel is a common cause of wheel breakage.

Wheels for stainless steel are made with very low iron, sulphur and chlorine content, usually marked INOX or with an equivalent note. This avoids contaminating the stainless surface, which can lead to rust spots later. They can also cut mild steel, but wheels for mild steel should not be used on stainless.