What size disc do you need?
Start here, because disc size decides almost everything else about the tool. Grinders are named after the disc they take, and in Australia you’ll mostly see three. 100mm (4-inch) is the small old standard, fading out. 125mm (5-inch) is the one to buy — it’s the size on the shelf everywhere, so the discs that fit it are in every hardware aisle and you’re never hunting an odd fitting. 230mm (9-inch) is the big two-handed beast for heavy cutting and demolition, and it’s more grinder than a home project ever needs.
The thread the disc bolts onto matters too. On a 125mm grinder it’s an M14 spindle — the spindle is the threaded shaft the disc screws onto, and M14 is the common size, so any 125mm disc fits. For the jobs most of us have — cutting bolts and tek screws flush, grinding a weld back, cleaning up rust, slicing the odd paver — a 125mm grinder does the lot. Buy the big 9-inch only if you know you’ve got real demolition ahead, and even then most people are better served by a smaller grinder plus the right disc.
Corded or cordless?
This used to be simple — corded for grunt, cordless for getting to the back fence. It’s closer now. A good brushless cordless grinder gets through the jobs a home project throws up without trailing a lead through the sparks. A corded grinder still wins on sheer pace through thick steel and never goes flat, so if you’re doing heavy cutting near a power point, corded gives you more grinder for less money.
For most people the deciding factor isn’t the grinder at all — it’s the battery. If you already own a cordless platform, buy the grinder that runs on your packs and you’ve saved yourself the most expensive part. If you haven’t picked a platform yet, that’s the bigger decision, and it’s worth reading the platform comparison before you spend, because every cordless tool you buy after this one shares the same battery.
Brushless or brushed?
You’ll see “brushless” on the dearer grinders and it’s worth understanding before you decide. A brushed motor has little carbon blocks that rub on the spinning part and slowly wear down, bleeding off power and eventually needing replacement. A brushless motor does away with them. It runs cooler, gets more work out of each charge, and lasts years longer. On a tool that lives inside its own cloud of grinding dust, that sealed-up design earns its keep.
It costs more up front. The plain way to think about it: if the grinder’s going to get regular use, brushless pays for itself in life and runtime. If it’s coming out twice a year for a small job, a brushed grinder is fine and you can pocket the difference. I go into the full trade-off in the brushless motors guide if you want the longer version.
The safety features that matter
This is the part I’d weigh hardest, because a 125mm disc spinning at around 8,500 rpm — revolutions per minute, how fast the disc turns — has no interest in your day. The failure mode that hurts people is kickback: the disc snags in the cut and the whole tool jerks back hard towards you. Better grinders fight that on a few fronts, and these features are worth paying for:
- Kickback detection uses sensors to spot the sudden jam and cut the power before the tool can twist out of your hands.
- Soft start winds the disc up to speed over a moment instead of lurching the instant you hit the switch, so the grinder isn’t trying to leap out of your grip on startup.
- Anti-restart stops the grinder powering straight back up after the battery’s pulled or the tool’s stalled — you have to switch it off and on again on purpose.
- A brake stops the disc fast when you let go, instead of letting it coast for several seconds.
None of that replaces the basics. Keep the guard on, match the disc to the grinder, and wear wrap-around safety glasses rated to the Australian standard (AS/NZS 1337) — a grinding disc throws sparks and grit straight at your eyes. SafeWork’s alert on keeping the guard on and the disc size matched to the grinder is the rule that keeps fingers attached, and it’s worth two minutes before your first cut. The electronics are a real layer of protection on top, not a substitute for the guard and your glasses.
Slide switch or paddle switch?
Two grinders with the same specs can feel completely different in the hand, and it usually comes down to the switch. A slide switch sits on top of the body and you push it forward to lock it on, so you’re not pinning a trigger down for a long job — easier on your hand over time. The catch is the grinder keeps running if you drop it. A paddle switch runs along the body and you squeeze it the whole time; let go — or drop the tool — and it cuts out instantly. That’s the safer behaviour, at the cost of a hand that tires faster on a long cut.
There’s no wrong answer, but know which you’re buying. A first-timer is usually better off with a paddle switch for the dead-man cut-out; someone doing long grinding sessions often prefers the slide switch and leans on kickback detection and anti-restart to cover the trade-off. The grinder in the tile above is a slide-switch one, and I still steer a first-timer to it because the kickback detection guards the failure mode that hurts people — the disc snagging and the tool kicking back at you. The switch staying on if you drop it is the trade-off that rides along with it, so keep both hands on the grinder and the guard on.
Match the disc to the job
The grinder’s only half of it — the disc does the work, and the wrong one is dangerous. Cutting discs are thin, for slicing metal. Grinding discs are thick, for taking material off a weld or a surface. Flap discs blend cutting and sanding for smoothing and finishing. The hard rule: never grind with a cutting disc. It’s not built for side load and it can shatter. Buy a couple of discs for the jobs you’ve got rather than relying on whatever came in the box, and check the disc’s printed size matches your grinder before it goes on.
What I’d buy
For nearly every DIYer: a 125mm brushless grinder with the safety electronics — kickback detection, soft start and anti-restart — on whatever battery platform you’ve already committed to. That covers cutting, grinding, rust and paint stripping, and the odd paver, without paying for a 9-inch you’ll use once. Add a thin cutting disc and a flap disc to whatever came in the box, wind the side handle in, and put your glasses on before the disc starts turning.
The grinder in the tile above is the one I land on when someone’s on the Makita platform and wants a safe, sensible 125mm skin — it’s the full review if you want the specifics. It’s not the cheapest grinder going, and it’s worth knowing exactly what the extra money buys: the brushless motor and the kickback electronics, on the broadest battery range in the shed. If you’re on a different platform, the same checklist holds — buy the 125mm brushless grinder with the safety gear that runs on your packs, and you’ll have bought right.
