Angle Grinder Cheat Sheet

Which disc, which grinder, and how to use it safely. Pick your material and job for the right disc, its RPM rating and the PPE, then print the one-page disc chart.

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Which disc do I need?

Material

Job

Grinder size

Use this disc

Cut-off wheel (Type 1 or 41)

4.5 in x 0.045 in (1 mm) thin cut-off wheel.

Thickness: 0.040 to 1/8 in (1 to 3 mm)
Disc rating: 13,300+ RPM
Grinder speed: About 11,000 RPM

Why: Thin wheels cut fast with less heat and less pinch. Support both sides of the cut so the kerf stays open.

PPE:

Full face shield over safety glasses
Hearing protection
Leather gloves
Long cotton or wool sleeves
N95 respirator for metal dust

Cut-off wheels break if you grind with the face. Change discs before grinding.

Save this disc setup to a project: the disc, a spare and the PPE on your shopping list, and the pre-start safety check on your phone.

Project plan · built from your numbers

Angle grinder: cut through mild steel

Cut through mild steel with a 4.5 in grinder and a cut-off wheel (type 1 or 41). Thin wheels cut fast with less heat and less pinch. Support both sides of the cut so the kerf stays open.

Materials: $40
Time: 1 to 2 hours
Level: Easy

5 steps 3 tools 6 materials

1
Pre-start safety check
Run this every time before the grinder touches the work.
- Disc rated 13,300 RPM or higher
- Disc not dropped, chipped or cracked
- Guard on and between you and the disc
2
Mount the disc
Unplug or pull the battery, lock the spindle, fit the flanges the right way round and snug the nut with the wrench.
3
Run it up
Stand to the side and run the grinder for 30 seconds at full speed before touching the work.

01 · Your numbers

Disc: Cut-off wheel
Grinder: 4.5 in (115 mm)
Disc rating: 13,300+ RPM
Thickness: 0.040 to 1/8 in

02 · The plan

5 steps · 3 tools · 6 materials

2 more steps, the full tool list and a shopping list you can check off as you go.

03 · Finished

Your plan is 60% built. Save it.

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Angle grinder: cut through mild steel

Finished in 1 to 2 hours · $40 DIY

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Angle grinder disc chart

Units:

Disc	Thickness	Use for	Never
Cut-off wheel (Type 1 or 41)	0.040 to 1/8 in	Cutting steel, rebar, bolts, pipe	Never grind with the face
Grinding wheel (Type 27)	1/4 in	Heavy stock removal, welds, burrs	Never cut with the edge
Flap disc (Type 27 or 29)	about 1/2 in	Blending welds, deburring, finishing	Never on masonry
Wire wheel or cup brush	n/a	Rust, paint, scale removal	Never without a face shield (wires fly)
Diamond blade, segmented rim	about 0.08 in rim	Concrete, brick, block, pavers	Never on steel
Diamond blade, continuous rim	about 0.06 in rim	Tile and porcelain, chip-free	Never on steel
Diamond blade, turbo rim	about 0.07 in rim	Stone and mixed masonry, fast and fairly clean	Never on steel
Diamond cup wheel	n/a	Grinding concrete high spots and edges	Never without a shroud and vacuum indoors

High-risk tool warning

Angle grinders are among the most dangerous power tools

Discs spin at 10,000+ RPM and can shatter
Cuts and grinding create hot metal sparks
High torque can throw the tool if disc catches
Serious injuries happen quickly - always use PPE

Read all safety information in this guide before operating an angle grinder.

Angle grinder sizes, speeds and disc ratings

Disc size	Grinder speed	Buy discs rated	Max cut depth
4.5 in	About 11,000 RPM	13,300+ RPM	1.1 in
5 in	About 11,000 RPM	12,250+ RPM	1.4 in
6 in	About 9,000 RPM	10,200+ RPM	1.8 in
7 in	About 8,500 RPM	8,600+ RPM	2.2 in
9 in	About 6,600 RPM	6,650+ RPM	3.2 in

4.5 in (115 mm) is the DIY standard. Always check the RPM printed on the disc is higher than the speed on the grinder's label.

Do all discs fit all angle grinders? Arbor and thread fit

Item	Fit	Note
Bonded wheels and diamond blades	7/8 in (22.23 mm) bore, held by the flange nut	Same bore on 4.5 to 9 in grinders; 9 in may use a 7/8 in bore too
Spindle thread, North America	5/8-11 UNC	Most US grinders (DeWalt, Milwaukee, Makita US)
Spindle thread, Europe, UK, Asia	M14 x 2.0	Metric; not interchangeable with 5/8-11
Wire cup brushes and threaded flap discs	Screw straight onto the spindle	Buy the thread that matches your grinder; remove the flanges first
Reducer bushings	7/8 in to 5/8 in or 20 mm	Only for wheels made for them; never on a grinder disc with a 7/8 bore

Flap disc grit ladder and grain

Fast stock removal, heavy welds

General grinding and weld blending

Blending and light deburring

120

Finishing before paint

Grain	Best on	Note
Aluminum oxide	Mild steel, wood, general use	Cheapest; wears fast on stainless
Zirconia	Steel and stainless, moderate pressure	Self-sharpening, best value for most DIY
Ceramic	Stainless and hard alloys, high pressure	Runs cooler and lasts longest; needs firm pressure

Stainless: keep a separate set of discs and wire brushes, marked INOX, for stainless only. A disc or brush that has touched carbon steel leaves iron in the surface that rusts within days.

Kickback and pinch: which way the disc pulls

The disc spins toward the guard side. If the kerf closes, it grabs and the grinder climbs back at you.
Support the work so the cut opens as you go: offcut free to drop, not clamped on both ends.
Stand to one side of the disc plane, never directly behind it.
Keep the side handle on and both hands on the tool.
Do not twist or lever a cut-off wheel in the kerf.

Disc Types & Applications

Grinding Discs (Thick - 1/4")

For metal removal, shaping, deburring
Use flat face for grinding, not edge
Work at 15-30° angle to surface
Never use for cutting

Cut-off Wheels (Thin - 1/16")

For cutting metal - pipe, rebar, sheet
Use perpendicular to material
Never grind with the flat face - will break
Let the wheel do the work - don't force

Flap Discs

Overlapping sandpaper flaps
Blending welds, removing paint, finishing
Available in various grits (40-120)
Longer lasting than grinding discs for smoothing

Wire Wheels & Cups

Rust removal, paint stripping
Cleaning welds, surface prep
Twisted wire for aggressive cleaning
Crimped wire for lighter work

Diamond Blades

Cutting concrete, brick, tile, stone
Continuous rim for smooth cuts in tile
Segmented rim for concrete/masonry
Turbo rim balances speed and smoothness

RPM Matching - Critical Safety

NEVER exceed the disc's rated RPM

A disc rated for 10,000 RPM on a 12,000 RPM grinder can shatter explosively.

How to Check

Disc RPM rating is printed on the disc
Grinder RPM is in the specifications
Disc rating must EXCEED grinder speed

Typical Speeds by Size

4-1/2": 10,000-12,000 RPM
5": 10,000-11,000 RPM
7": 8,000-8,500 RPM
9": 6,000-6,500 RPM

Safety Requirements

Required PPE

Face shield: Not just glasses - discs can shatter
Leather gloves: Sparks are hot metal particles
Long sleeves: Natural fibers, not synthetic (melts)
Hearing protection: Loud tool, especially cutting
Closed-toe shoes: Hot sparks fall down

Guard Position

Guard must always be between you and the disc
Adjust guard position as you work
NEVER remove the guard

Safe Operation

Inspect disc for damage before each use
Never use dropped disc (may have hairline cracks)
Let disc reach full speed before contacting work
Use two hands at all times
Don't lock the trigger in ON position
Let disc stop completely before setting down

Fire Prevention

Clear area of flammable materials before grinding
Sparks can travel 20+ feet and stay hot
Watch for sparks landing in hidden areas
Keep fire extinguisher accessible
Check area for smoldering after work

How to change an angle grinder disc

Step-by-Step

Unplug grinder (or remove battery)
Press spindle lock button
Use wrench to loosen flange nut
Remove old disc
Check new disc for damage and RPM rating
Install with correct flange orientation
Tighten firmly but don't overtighten

Important Notes

Some discs have directional arrows - follow them
Paper blotter/ring faces the flanges, not disc face
Never use without flanges properly installed

Common Operations

Cutting Metal

Use cut-off wheel (thin disc)
Support work so it doesn't pinch blade
Keep disc perpendicular to cut
Let disc cut - don't force or twist

Grinding Welds

Use grinding disc or flap disc
Work at 15-30° angle
Keep moving - don't dwell in one spot
Check temperature - don't overheat workpiece

Rust Removal

Use wire wheel or cup brush
Flap disc for smooth finish after
Keep tool moving to avoid gouging

Cutting Masonry/Tile

Use diamond blade
Score line with multiple passes for tile
Use water to reduce dust if possible
Wear respirator - silica dust is hazardous

Additional Information

About This Angle Grinder Guide

The angle grinder is an incredibly versatile tool that cuts, grinds, polishes, and cleans metal and masonry. It's essential for metalworking, welding, and many construction tasks. However, it's also one of the most dangerous power tools available to DIYers.

The high RPM and exposed disc create serious hazards. Discs can shatter if damaged, overloaded, or run above their rated speed. Hot sparks can start fires or cause burns. The high torque can throw the tool if the disc catches on material. These aren't theoretical risks - they happen regularly to experienced users who get complacent.

This guide emphasizes safety because proper technique and PPE are non-negotiable with angle grinders. Understanding disc types, RPM matching, and proper operation keeps you safe while you take advantage of this powerful tool.

Related guides

Cutting pipe in a tight spot where a grinder is the wrong tool? Use the reciprocating saw cheat sheet. For PPE across every tool see power tool safety, and for blades across every saw the blade matrix. Cutting tile or pavers? Estimate them with the tile calculator or the concrete calculator.

Frequently Asked Questions

Can I use a cut-off wheel for grinding?

No. Cut-off wheels are about 1 mm (0.045 in) thick and made only for cutting with the edge. Grind with the flat face and the wheel can shatter. Swap to a 1/4 in grinding wheel or a flap disc.

Why did my disc shatter?

Common causes: a disc rated below the grinder's RPM, a dropped or cracked disc, side-loading a cut-off wheel, the disc pinching in the cut, or loose or missing flanges.

Do I really need a face shield?

Yes. When a disc shatters, pieces fly in every direction, not just at your eyes. Wear a full face shield over safety glasses.

What's the difference between grinding and flap discs?

Grinding wheels remove metal fast and leave a rough surface. Flap discs remove metal more slowly, leave a smoother finish and are harder to gouge with. Grind heavy, then blend with a flap disc.

Can I cut concrete with an angle grinder?

Yes, with a segmented diamond blade. A 4.5 in grinder cuts about 1 in deep. The dust is crystalline silica, so cut wet or use a shroud and HEPA vacuum, and wear a P100 respirator.

What size angle grinder should I buy?

A 4.5 in or 5 in grinder covers almost all DIY work: cutting bolts, rebar and tile, grinding welds, and stripping rust. Buy a 7 or 9 in only for deep masonry cuts, and only if you can handle it two-handed.

Can an angle grinder cut tile?

Yes, with a continuous-rim diamond blade. Mark the cut, score a shallow first pass to stop chipping, then cut through. Cut wet or outdoors and wear a respirator.

How long does a cut-off wheel last?

A 4.5 in x 0.045 in wheel makes roughly 20 to 40 cuts through 1/2 in rebar, fewer on stainless. Replace it when it is worn to about 1 in from the flange, or sooner if it is chipped.

Can I use a 5 in disc on a 4.5 in grinder?

No. The guard will not cover it, and a bigger disc on a faster small grinder can be over its rated speed at the rim. Use the disc size the grinder and guard were made for.

Corded or cordless for cutting rebar?

Either works for a few cuts. A modern 18 or 20 V brushless grinder cuts a few dozen bars of 1/2 in rebar per 5 Ah battery. For a full day of cutting, a corded grinder never runs flat.

Do all discs fit all angle grinders?

Most bonded wheels and diamond blades have a 7/8 in (22.23 mm) bore and fit any 4.5 to 7 in grinder of the right size. Threaded accessories (wire cups, some flap discs) must match the spindle: 5/8-11 in North America, M14 in Europe and Asia.

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