Short answer: Fit a disc that matches your grinder in diameter, arbor and speed rating. Guard on, glasses on, both hands on the tool. Let the disc reach full speed before it touches anything, use light pressure, keep the disc square in the cut and cut away from your body. Unplug the tool or pull the battery before you change a disc. Do that every time and an angle grinder is one of the most useful tools you own.
What is an angle grinder used for?
Cutting metal, stone, concrete, tile and glass. Shaping wood. Grinding welds flat, removing rust and paint, sharpening mower blades and axes, cleaning up masonry. The tool is the same for all of that. What changes is the disc, and choosing the right one is most of the skill.
What are the parts I need to know?
- Spindle. The threaded shaft the disc sits on.
- Inner flange and lock nut. Clamp the disc to the spindle. The nut comes off with the two-pin wrench, or by hand with a quick-lock nut.
- Spindle lock. A button that stops the spindle turning while you loosen the nut.
- Guard. The steel shield over half the disc. It rotates so you can point it between the disc and your body. It stays on.
- Side handle. Screws into either side of the head. Fit it. A grinder is a two-handed tool.
- Switch. A paddle you hold or a slider that locks on. Paddle switches stop the tool the moment you let go, which is what you want as a beginner.
How do I fit or change a disc?
- Unplug the tool or remove the battery. Not just switched off. Unplugged.
- Check the disc. Read the label: diameter, arbor hole and maximum RPM. All three must suit your grinder, and the disc's RPM rating must be higher than the tool's speed. Ours are 4 inch (100 mm), 5/8 inch (16 mm) arbor, rated to 12,225 RPM. Will This Disc Fit My Grinder? shows where to find your tool's numbers.
- Inspect it. Chips at the rim, hairline cracks near the hole, or a hard drop in its past: retire it.
- Press the spindle lock and loosen the lock nut with the wrench.
- Seat the disc on the inner flange, label facing the way the manual shows, then tighten the nut firmly. Hand tight plus a snug turn with the wrench. Do not hammer it.
- Set the guard so it sits between the disc and you.
- Test run. Plug in, hold the tool away from you and anyone else, run it for thirty seconds. Vibration or wobble means stop, unplug and check the seating.
How do I hold it?
Two hands, always: one on the body behind the switch, one on the side handle. Feet apart, weight balanced, the tool in front of you rather than off to one side. Point the guard so sparks and debris go away from you and away from the cord. Keep the cord behind you where the disc cannot reach it.
Stand slightly to the side of the disc's plane rather than directly behind it. If a disc ever comes apart, the fragments travel in that plane.
How do I make my first cut?
- Mark the line with a marker or chalk.
- Clamp the work in a vise or to the bench, with both sides of the cut supported so the offcut cannot sag and pinch the disc.
- Gear on: safety glasses, ear protection, gloves, a respirator for stone or wood dust.
- Full speed first. Switch on with the disc clear of the work and let it reach full speed.
- Touch down lightly on the line, disc square to the surface, and let the speed do the cutting. Your job is to guide, not to press.
- Straight lines only. If you need a curve, make a series of straight relief cuts.
- Finish the cut rather than snapping the last bit off, then lift the tool out and let the disc stop completely before you set it down.
What causes kickback, and how do I avoid it?
Kickback is the disc binding in the cut and the tool jumping toward you. Three things cause it: the cut closing on the disc because the offcut sagged, twisting the disc sideways in the cut, and using a disc that is wrong for the material or damaged. Support both sides, keep the disc square, use the right disc. The full list of what breaks discs, and how to stop it, is in Why Do Cutting Discs Break?
Which disc for which job?
| Job | Disc |
|---|---|
| Cutting steel, rebar, pipe, aluminum | Metal cutting disc |
| Cutting concrete, brick, pavers, granite | Concrete and stone cutting disc |
| Cutting ceramic and porcelain tile | Tile cutting disc |
| Cutting glass and mirror | Glass cutting disc |
| Shaping and carving wood | Wood carving disc |
| Grinding welds, beveling steel | Grinding wheel (Type 27, depressed center) |
| Sanding, blending, rust removal | Flap disc or wire cup (never for cutting) |
Cutting discs are for cutting. Do not grind on the flat face of a thin cutting disc: that is side load, and it is how they break. Diamond Blade for an Angle Grinder explains the rim types if you want to go deeper.
What safety gear is non-negotiable?
- Guard fitted. Every time. It takes seconds with a quick-lock guard.
- Safety glasses, wraparound. Sparks and fragments come from every angle.
- Ear protection. A grinder on steel runs well past 100 dB.
- Gloves for grip and sharp edges. Leather or cut resistant, never loose knit that can catch.
- Respirator for stone, concrete and wood dust.
- No loose sleeves, no jewelry, hair tied back.
The seven rules that prevent real injuries are in Angle Grinder Safety: 7 Rules That Prevent Real Injuries.
The short version
Right disc, guard on, two hands, full speed before contact, light pressure, square in the cut, unplug to change discs. Learn that on scrap before the real job, and the grinder will do more for you than any other tool in the box.
Start with the right disc: Cutting Discs for Angle Grinders
