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.
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.
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.
How do I avoid heat marks and blue discolouration when grinding stainless steel?
Stainless conducts heat poorly, so heat builds up in the surface and can leave a blue or straw tint that is hard to remove and can reduce corrosion resistance. Use as little contact pressure as you can, keep the disc moving rather than dwelling in one spot, and avoid slow, heavy grinding.
Use a disc made for stainless steel and replace a disc that has glazed or stopped cutting, as a blunt disc rubs and generates more heat. Where possible let the work cool between passes, or cool it. Check the markings and the maker's instructions for the metal you are working on.
Is a thicker grinding disc better than a thinner one?
Thickness is a trade-off. Thicker discs generally give longer life and suit heavy, aggressive work such as bevelling and weld removal. Thinner discs can be more manoeuvrable and suit lighter weld dressing, but they wear faster.
The disc must always suit the grinder: the diameter, bore and the maximum speed marked on the disc must match the guard and the speed on the grinder's data plate. Do not choose by thickness alone, and do not remove a guard to fit a bigger disc. Follow the manufacturer's recommendations for the metal and the task.