Grinding Discs FAQs
Answers on how depressed-centre grinding discs and bench grinder wheels are built, chosen, fitted and used on steel, stainless steel and aluminium.
What is a depressed-centre grinding disc and what is it made for?
It is a reinforced, resin-bonded disc with a raised hub so the grinder's nut and flange sit below the face. It is used mainly on hand-held angle grinders to remove metal, for example taking down a weld, dressing a casting or bevelling an edge. The grinding face is used flat to the work at a modest angle.
It is not a cutting wheel. Wheels for cutting-off are thinner and are a different type. Always check the markings on the disc for its approved use, maximum speed and any restrictions, and the manufacturer's instructions before fitting.
Why do grinding discs have glass fibre layers inside?
Discs for heavy grinding are normally reinforced with resin-coated woven glass fibre mat. The reinforcement lets the disc withstand the high stresses of hand-held grinding and helps hold fragments together if a disc does break.
That is why only discs made for hand-held use, with the right bond and reinforcement, should go on an angle grinder. The reinforcement is not a reason to relax: the guard must always stay fitted, you must stay within the speed marked on the disc and the disc should be replaced if it is damaged. Do not try to use bench grinder wheels or other unsuitable wheels on a hand-held grinder.
Can I use a grinding disc on its edge to cut a slot or a bar?
No, not unless the disc is marked as suitable for both grinding and cutting. Grinding discs and cutting-off wheels are different types, made for different loads. A grinding disc is designed to work on its face, and loading it sideways in a cut risks cracking or breaking it.
If you need to cut, use a reinforced cutting-off wheel approved for hand-held machines. Look at the markings on the disc for restrictions, which can include not for face grinding or not for hand-held cutting, and obey them. If in doubt, read the maker's instructions.
What angle and pressure should I use for grinding?
Hold the disc at a modest angle to the work, as the disc maker's instructions describe, and use light, steady pressure so the disc does not grab or kick. Let the grinder reach full speed before it touches the metal, keep it moving and hold it with both hands.
Pushing hard does not speed things up much and risks overloading the disc, overheating the work and losing control. If a disc snags, switch off and let it stop fully before freeing it. Stay out of the line the grinder would travel if it kicked back.