Bench grinder

How it works

The motor turns the abrasive wheels at a fixed speed, and the operator holds the workpiece or tool against the wheel face, supported by an adjustable work rest. A guard encloses most of the wheel, leaving only a limited angle of the periphery exposed, and an adjustable tongue at the top of the guard is brought close to the wheel as it wears. The wheel removes metal by the cutting action of its abrasive grains, which are held in a bond.

In its earlier forms, the grinding wheel was turned by human or water power. The American Precision Museum describes the sequence in its collection: a treadle-powered grinding wheel patented by James L. Lord in 1854, pedal-powered machines from the 1870s and 1880s, and a water-powered grinder of the Jones and Lamson factory, driven from a water wheel in the basement through gears and belts. The museum says that grinders now typically run on electricity.

Anatomy

Motor and spindle: The wheel is mounted on the machine spindle. Federal regulation requires that the spindle be made to the nominal size plus zero, minus 0.002 inch, with the wheel hole made suitably oversize to allow for heat and pressure.
Abrasive wheel: Mounted between flanges; marked with the maximum operating speed.
Flanges: Federal regulation requires all abrasive wheels to be mounted between flanges not less than one-third the diameter of the wheel, dimensionally accurate and in good balance.
Safety guard: Covers the spindle end, nut and flange projections and encloses the wheel except for a limited exposure.
Adjustable tongue: The peripheral member at the top of the guard that is adjusted as the wheel diameter decreases.
Work rest: A rigid, adjustable support for the work in offhand grinding, kept close to the wheel.
Visor or eye shield: An accessory; the regulation says visors and similar equipment are not counted as part of the guard when measuring guard opening unless they have strength equal to the guard.

Variants

Bench stand: The bench and floor stand grinders are the machines to which the regulation’s 90-degree guard exposure applies.
Pedestal or floor stand grinder: The same machine on a floor stand; VintageMachinery.org lists bench and pedestal grinders among Stanley Electric Tools metalworking machines, some made for Stanley by Kingston-Conley Electric Co.
Treadle and pedal grinder: Human-powered grinders on a frame; the American Precision Museum holds an 1854 treadle machine and a probably homemade pedal machine.
Water-powered grinder: Driven from a water wheel through gears and belts; an example from the Jones and Lamson factory is in the American Precision Museum collection.
Motor-spindle polishing lathe: A 1924 patent application describes lathes in which the motor’s armature shaft serves as the spindle that mounts the grinder or buffing wheel.

Specifications

Work rest opening (maximum) · in: 1/829 CFR 1910.215(a)(4).
Tongue guard clearance (maximum) · in: 1/429 CFR 1910.215(b)(9): the distance between the wheel periphery and the adjustable tongue shall never exceed one-fourth inch.
Guard exposure, bench and floor stands · degrees: 90 degrees or one-fourth of the peripheryThe exposure begins at a point not more than 65 degrees above the horizontal plane of the spindle; where the work requires contact below that plane the exposure shall not exceed 125 degrees (29 CFR 1910.215(b)(3)).
Flange diameter (minimum) · fraction of wheel diameter: one-third29 CFR 1910.215(c)(1).
Wheel diameter and speed · in / rpm: The spindle speed must not exceed the maximum operating speed marked on the wheel; no typical value is sourced.

Made to

OSHA 29-CFR-1910-215
ANSI B7.1
EN 12413
ISO 525
IEC 62841-3-4

Safety and care

Safety

The regulation requires a safety guard covering the spindle end, nut and flange projections on grinding machines, with the exposure angles it specifies.
The regulation requires work rests on offhand grinders, kept adjusted to a maximum opening of one-eighth inch to prevent the work from being jammed between the wheel and the rest, which may cause wheel breakage.
The regulation requires the work rest to be securely clamped after each adjustment and prohibits making the adjustment with the wheel in motion.
The regulation requires the adjustable tongue at the top of the guard to be kept within one-fourth inch of the wheel as the wheel diameter decreases.
The regulation requires that the spindle speed be checked before mounting a wheel to be certain it does not exceed the maximum operating speed marked on the wheel.
The regulation provides that a wheel that sounds cracked or dead shall not be used.

Tips

Ring test every wheel before mounting
The regulation sets out the test: tap the wheel gently with a light nonmetallic implement, such as a screwdriver handle for light wheels or a wooden mallet for heavier wheels, at about 45 degrees on each side of the vertical centerline and 1 or 2 inches from the periphery, then rotate the wheel 45 degrees and repeat. A sound wheel gives a clear metallic tone; a cracked wheel gives a dead sound.1
Test dry wheels, and expect organic-bonded wheels to ring less
The regulation notes that wheels must be dry and free from sawdust when the ring test is applied, otherwise the sound will be deadened, and that organic bonded wheels do not emit the same clear metallic ring as vitrified and silicate wheels.1
Fit the wheel freely on the spindle
The regulation requires grinding wheels to fit freely on the spindle and remain free under all grinding conditions, so that a controlled clearance between the wheel hole and the spindle avoids excessive pressure from mounting and spindle expansion.1
Use blotters where the wheel needs a compressible facing
Where blotters or compressible flange facings are required, the regulation says they must cover the entire contact area of the flanges, and it lists wheels that do not need them, among them mounted wheels, abrasive discs and types 27 and 28 wheels. Contact surfaces of wheels, blotters and flanges must be flat and free of foreign matter.1
Inspect the guard and rest as part of every check
OSHA’s checklist for abrasive wheel grinders asks whether the work rest is kept within 1/8 inch of the wheel and whether the adjustable tongue guard on the top side is kept within 1/4 inch of it, and these gaps open as the wheel wears.1 2

History

Earliest documented

ninth century (earliest known illustration of a crank-operated grinding wheel)

Carolingian Europe (Utrecht Psalter)

The American Precision Museum states that the earliest known illustration of a grinding wheel, operated by a crank handle, appears in the Utrecht Psalter, a ninth-century illuminated manuscript, and that archeologists have found grinding stones used to process seeds and nuts dating back as far as 30,000 years ago in New South Wales. The museum shows a sword being ground in the twelfth-century Eadwine Psalter, which includes colored copies of images from the Utrecht Psalter.1

The abrasive wheel is far older than the electric grinder. The American Precision Museum notes that grinding stones for processing seeds and nuts date back some 30,000 years, and that the earliest known picture of a crank-operated grinding wheel is in a ninth-century manuscript. The wheel of that picture and the wheel of the bench grinder share the same use, which is to shape and sharpen metal by holding it against a spinning stone.

What changed over the centuries was the power source and the wheel itself. The museum traces human power through treadles and pedals to water power: treadles had the drawback that the foot must stop and lose momentum at each stroke, the pedal grinders of the 1870s and 1880s corrected that, and a water wheel in a factory basement turned grinders upstairs through gears and belts until reliability problems with early waterpower led manufacturers toward turbines and steam. Roe records the change in the wheel: F. B. Norton began experimenting on vitrified emery wheels about 1873 and sold them from 1879, and Roe credits F. B. Norton with founding the grinding wheel industry.

The bench grinder is the form that results when an electric motor’s shaft replaces the line shaft. R. C. Mitchell’s 1924 application states that the usual construction of lathes with built-in motors was to use the armature shaft as the spindle for the grinder or buffing wheel, and that the objection to it was a constant motor speed that is not always the most desirable. Stanley’s electric tool line of the 1930s and later included bench and pedestal grinders. The sources read do not show who first mounted two wheels on a motor shaft as a general-purpose bench tool or when.

Hazards define the modern form as much as the mechanism does. The federal regulation for abrasive wheel machinery prescribes the guard, its exposure angle, the tongue that follows the wheel as it wears, the flange size and the work rest, and it states the reason for the work rest rule: work jammed between the wheel and the rest may cause wheel breakage. The ring test, the speed-marking rule and the spindle tolerance in the same regulation show that the wheel is treated as a part that can fail in service and that must be checked before use.

Timeline

ninth century
The Utrecht Psalter shows a crank-operated grinding wheel, the earliest known illustration, according to the American Precision Museum.1
1854
James L. Lord patents a treadle-powered grinding wheel, an example of which is in the American Precision Museum collection.1
1870s–1880s
Pedal-powered grinders begin to appear, letting the operator work without stopping the foot at each stroke.1
c.1873
F. B. Norton begins experimenting with vitrified emery wheels in Worcester, Massachusetts; the wheels are put on the market in 1879.1
1885
F. B. Norton dies; the business is incorporated as the Norton Emery Wheel Company, now the Norton Company, according to Roe.1
1924
R. C. Mitchell of Springfield, Ohio, files the application for a grinding and polishing lathe; the specification (patent issued 1931) says that in lathes with a built-in driving motor the usual construction has been to use the motor’s armature shaft as the spindle for mounting the grinder or buffing wheel.1
after 1929
Stanley Electric Tools, formed in 1929, lists bench and pedestal grinders among its metalworking machines; some are made for Stanley by Kingston-Conley Electric Co.1

Gaps in the record (6)

The date and inventor of the electric bench grinder were not found in any primary source; the first appearance of the two-wheel motor-shaft grinder is not documented here.
The Utrecht Psalter dating and the medieval history of the grindstone are known through the American Precision Museum alone; the original manuscript and Lynn White’s Medieval Technology and Social Change were not read.
No manufacturer’s manual for a current bench grinder could be fetched, so manufacturer operating instructions (wheel dressing, wheel selection, rest height) are not used; care is empty.
Wheel specifications (grit, grade, bond, markings) and the ANSI B7.1 standard text were not sourced.
The regulation text is read from the Legal Information Institute copy of 29 CFR 1910.215; the date of its adoption was not established.
No independent test data on bench grinders were found, so there is no buying section.