Angle grinder

How it works

An abrasive or cutting disc is mounted at a right angle to the motor and rotates rapidly, with an adjustable guard over part of the disc and a side handle for two-handed operation, according to an OSHA-supported toolbox talk. A right-angle gearbox turns the motor’s rotation through ninety degrees to the spindle. FLEX, the manufacturer that introduced the high-speed angle grinder, says its discs turn at up to 13,300 revolutions per minute for 115 mm discs and up to 12,200 for 125 mm discs.

The disc is held on the spindle between flanges. OSHA’s portable-tool rule requires that abrasive wheels be used only on machines with safety guards, that the guard cover the spindle end, nut and flange projections except on machines designed for certain wheel types, and that on right-angle or vertical portable grinders the guard have a maximum exposure angle of 180 degrees and sit between the operator and the wheel so that pieces of a broken wheel are deflected away. CCOHS describes the working posture of a right-angle grinder as holding the face of the wheel or disc at between 5 and 15 degrees to the surface.

Anatomy

Motor housing: Holds the electric motor; the OSHA toolbox talk notes that angle grinders may also be gas-powered or pneumatic, and FLEX makes corded and cordless models.
Angle head (gearbox): Turns the drive through a right angle to the spindle. FLEX says an angular gearbox replaced its flexible shaft at the end of the 1920s.
Spindle and flanges: The disc is mounted between flanges; 29 CFR 1910.215 requires wheels to be mounted between flanges not less than one-third the diameter of the wheel, with a smaller minimum for cutting-off wheels.
Guard: Covers part of the disc; 1910.243 limits the exposure of the wheel on right-angle portable grinders to 180 degrees.
Side handle: An auxiliary handle for two-handed operation; FLEX offers a vibration-reducing handle it calls SoftVib.
Switch: Includes, on some models, a paddle switch with dead-man function that FLEX lists among its cordless grinders.
Disc or wheel: A bonded abrasive grinding or cutting wheel; CCOHS also lists wire brushes, sanding pads and buffing pads as attachments.

Variants

By disc diameter: FLEX describes discs from 125 mm to 230 mm and 115 mm; 115 and 125 mm are the sizes for which it gives speed limits.
Constant-speed and variable-speed: FLEX makes both, and its history page lists a first cordless angle grinder with variable speed.
Corded and cordless: FLEX launched its first cordless angle grinder, 18 volt, in 2017, and its history page also lists a first 230-volt angle grinder with a brushless motor.
Long-neck (wall and ceiling) grinder: FLEX says it was the first power tool manufacturer in Europe to introduce a long-neck grinder for work on walls and ceilings, the FLEX Giraffe, in 1997.
Pneumatic and gas-powered: Listed by the OSHA toolbox talk as alternatives to electric power.
Horizontal and vertical grinders: CCOHS distinguishes the right-angle grinder from the horizontal grinder, whose wheel face lies fully on the work, and the vertical grinder, whose wheel face is in contact with the surface.

Specifications

Disc diameter · mm: 115–230Range given by FLEX, which also gives speed limits for 115 and 125 mm discs.
Maximum disc speed · rpm: FLEX: up to 13,300 for 115 mm discs and up to 12,200 for 125 mm discs. CCOHS says the maximum speed is marked on every grinder and any attachment must be rated at that speed or greater.
Working angle to the surface · degrees: 5–15CCOHS, for the right-angle grinder and for sanding pads.
Flange diameter · fraction of wheel diameter: at least 1/3 (1/4 for cutting-off wheels)29 CFR 1910.215.
Wheel shelf life · years: 3 (usual)CCOHS: an expiry date is stamped on the wheel, usually 3 years from manufacture.

Made to

ANSI B7.1
EN 60745-2-3
EN 12413
IEC 62841-2-3

Safety and care

Safety

OSHA 1910.243 requires guards on portable abrasive wheel machines, with a maximum exposure angle of 180 degrees on right-angle grinders and the guard placed between the operator and the wheel and adjusted so that pieces of a broken wheel are deflected away.
Before mounting, wheels must be inspected and sounded by the user by tapping with a light nonmetallic implement (the ring test of 29 CFR 1910.215(d)); a wheel that sounds cracked or dead is not used. CCOHS says ring tests do not apply to wheels 10 cm (4 in.) or smaller.
The spindle speed must not exceed the maximum operating speed marked on the wheel (29 CFR 1910.243(c)); CCOHS says not to use a wheel or attachment rated below the grinder’s speed.
OSHA’s toolbox talk lists the hazards of angle grinders as flying particles, dust and fumes, kickback, fire and explosion, electric shock, cuts, noise and musculoskeletal disorders, and says to use two hands, let the grinder reach full speed before use and stop before setting it down, and not to use liquid coolants.
CCOHS advises eye and face protection, tight-fitting gloves, protective footwear, hearing and respiratory protection as required, a firmly secured workpiece, no grinding near flammable materials without a hot work permit, and not clamping a portable grinder in a vise to grind hand-held work.

Care

CCOHS advises storing portable grinders on racks or hooks, inspecting the tool and attachments for damage before each use, servicing according to the manufacturer’s recommendations and recording maintenance.
CCOHS advises measuring the speed of electrically driven grinders monthly and after repairs, and measuring any new machine.
CCOHS advises storing cutting discs in a clean, dry area protected from moisture, temperature extremes and impact.

Tips

Hold the disc at 5 to 15 degrees
CCOHS gives 5 to 15 degrees between the face of the wheel or disc and the surface as the working angle of a right-angle grinder, and the same range for sanding pads, which it says gives even sanding and avoids gouging.1 2
Read the date stamped on the wheel
CCOHS says to verify whether an expiry date is stamped on the wheel; it is usually three years from the date of manufacture.1
Keep the mounting blotters
CCOHS says to use the mounting blotters supplied with a wheel, and to keep flange surfaces clean and flat, hand-tightening the mounting hardware so the disc is mounted flat without damaging the wheel.1
Seat a new wheel at speed first
CCOHS says to run a newly mounted wheel at operating speed for one minute before grinding and to stop and disconnect the grinder at once if it vibrates, wobbles or makes unusual noises.1
Let light pressure do the cutting
CCOHS says to apply light and steady pressure when cutting and not to force the disc, which may cause it to bind, overheat or shatter; it gives similar advice for wire brushes, letting the wire tips do the work.1
Use cutting discs for cutting and grinding discs for grinding
The OSHA-supported toolbox talk says a cutting disc should not be used for grinding. OSHA’s rule treats cutting-off wheels as a separate category, with their own flange sizes and, for some wheel types, an exposed spindle end.1 2 3
One tool, several attachments
CCOHS lists interchangeable cutting discs, grinding wheels, sanding pads, buffing pads and wire brushes. A sanding pad needs the correct backing plate, a wire brush the correct arbor size, and for a wire brush it advises operating at the correct angle for minimal wear.1

History

Earliest documented

1954 (high-speed angle grinder, per the manufacturer); 1922 (flexible-shaft hand-held grinder)

Stuttgart-Bad Cannstatt, Germany (Ackermann + Schmitt)

FLEX, the successor to Ackermann + Schmitt, says the history of the angle grinder begins in 1954, when Ackermann + Schmitt launched the first high-speed angle grinder, the DL 9. It also says that on 7 December 1922 Hermann Ackermann and Hermann Schmitt founded the company in Bad Cannstatt to make the MS 6 hand-held grinding machine with a flexible shaft, that at the end of the 1920s an angular gearbox replaced the flexible shaft to give the angle grinder, and that a low-speed angle grinder reached the market in 1935. These are the manufacturer’s own statements; no independent patent or museum record has been read.1 2 3

The angle grinder joins two older technologies, the bonded abrasive wheel and the portable motor. The wheel came first: the Norton Company’s history places the first vitrified emery wheel in Worcester in 1873 and its patent in 1877, and Acheson’s 1893 patent offered artificial carborundum as a substitute for diamonds and other abrasive material. The portable drive that FLEX describes came next, a hand-held motor turning a flexible shaft, which gave the company and then the tool its name. The company says it replaced the shaft with an angular gearbox at the end of the 1920s.

The tool’s defining step, in the manufacturer’s account, was speed. FLEX says Ackermann + Schmitt sold a low-speed angle grinder from 1935 and a high-speed model, the DL 9, from 1954, and that the DL 9 became the company’s main product. It says the brand name became the generic term for the tool, with the verb “flexing” replacing the cumbersome “cut-off grinding” in everyday speech, and that the name was added to the Duden dictionary in 2006. These are the company’s claims and are attributed to it; the claim to be first is not corroborated by an independent source read for this entry.

The tool is regulated through its wheel and its guard. OSHA’s portable-tool rule requires guards on abrasive wheel machines, limits the guard opening on right-angle grinders to 180 degrees and requires the guard to sit between the operator and the wheel. It requires every wheel to be inspected and sounded before mounting and the spindle speed to be checked against the wheel’s marked maximum, and it incorporates ANSI B7.1-1970 for guard design. CCOHS and an OSHA-supported toolbox talk add that the wheel’s rated speed must be at least the grinder’s, and the toolbox talk lists kickback among the hazards.

The tool changed in materials and power source more than in principle. FLEX says cast iron housings gave way to modern plastics, tools became lighter and handier, and motor power rose, and that the angle grinder principle is used in other machines. Its current line lists anti-kickback features, an electronic brake, brushless motors and a vibration-reducing side handle, and it launched a cordless model in 2017.

The angle grinder is used across trades. O*NET’s Tools Used table lists power grinders in 17 of the 24 occupations mapped to this archive’s trades, including welders, machinists, masons, plumbers and automotive technicians; the table’s commodity does not separate angle grinders from other power grinders. The disc fitted determines the work: CCOHS lists cutting discs, grinding wheels, wire brushes, sanding pads and buffing pads as attachments.

Timeline

1873
Swen Pulson fires a vitrified emery-and-clay wheel in the Norton pottery kiln in Worcester, Massachusetts; Frank Norton patents the process in 1877 and production begins in 1878.1
1893
Edward Acheson is granted US Patent 492,767 for artificial crystalline carbonaceous material, named carborundum, offered as a substitute for diamonds, bort and other abrasive material.1
1922
Ackermann + Schmitt is founded in Stuttgart-Bad Cannstatt on 7 December to make the MS 6 hand-held grinding machine with a flexible shaft.1 2
late 1920s
An angular gearbox replaces the flexible shaft in the company’s hand-held grinders, according to FLEX, giving the angle grinder.1
1935
A low-speed angle grinder is launched, according to FLEX.1
1954
Ackermann + Schmitt launches the DL 9, which FLEX describes as the first high-speed angle grinder on the market.1 2
1970
The 1970 edition of ANSI B7.1, Safety Code for the Use, Care, and Protection of Abrasive Wheels, is the edition OSHA incorporates by reference for abrasive wheel machinery guard design.1
1996
Ackermann + Schmitt becomes FLEX.1
1997
FLEX introduces the long-neck Giraffe grinder for walls and ceilings, which it says was the first of its kind from a power tool manufacturer in Europe.1
2006
The brand name “FLEX” is included in the Duden dictionary, according to FLEX.1
2017
FLEX launches its first cordless angle grinder, an 18-volt model.1

Where the sources disagree

When did the angle grinder begin?

The history of the angle grinder begins in 1954 with the DL 9, the first high-speed angle grinder.1
FLEX, on its “70 years angle grinder” page
An angular gearbox replaced the flexible shaft at the end of the 1920s, giving the angle grinder, and a low-speed angle grinder followed in 1935; the high-speed model came in 1954.1
FLEX, on its press page

Gaps in the record (7)

All dates for the first angle grinders come from the successor company, FLEX; no patent for the 1920s gearbox grinder, the 1935 low-speed grinder or the DL 9 has been read, and competing claims by other makers have not been examined.
Whether angle grinders displaced the cutting torch, the bench grinder or the abrasive saw for particular tasks is not sourced.
No Science Museum Group or other museum record of an early angle grinder was located.
The development of reinforced resin-bonded cutting and grinding discs, flap discs and wire wheels is not sourced.
Standard slugs are guesses; ANSI B7.1 is cited through OSHA’s incorporation by reference of the 1970 edition, and the current edition and the European and IEC standards for angle grinders and wheels have not been read.
No independent test of angle grinders is cited, so buying is null.
The corded-or-cordless argument has not been researched here beyond FLEX’s statement of its first cordless grinder in 2017.