Offhand Grinding

Offhand grinding guides the work by hand

A bench grinder mounts on a bench; a pedestal grinder stands on a base. In offhand grinding, the operator guides the work against the wheel, usually supported by a tool rest. This suits shaping and sharpening; it does not provide the controlled workholding and feeds of Precision Grinding.

For a conventional straight bench wheel, the intended grinding surface is usually its outer circumference. Move the work across that surface to distribute wear. Use only the surfaces approved for that wheel and machine; a wheel designed for peripheral grinding is not automatically suitable for side grinding.

Before operating, use Equipment Operating Procedure. Injury hazards and protective measures belong in Machine Hazards and Housekeeping, Personal Protective Equipment and Metal Chips and Swarf. This page explains the process, not a machine-specific operating authorization.

Wheel wear changes both rest and tongue-guard clearances

The tool rest supports the work near the wheel. The tongue guard is the adjustable part of the surrounding guard above the working opening; it is not the transparent eye shield. As the wheel becomes smaller, both clearances need checking and adjustment to the applicable machine instructions and requirements.

Make these adjustments with the wheel stopped and the machine secured according to its operating procedure. Recheck after dressing or wheel replacement. Use the specified clearance limits, not the proportions in the drawing.

Where to check the clearance requirements

OSHA's abrasive-wheel machinery requirements address work rests and adjustable guards. Consult the applicable text and the machine manual for the dimensions and scope.

Inspection, ring testing and dressing do different jobs

Inspection checks condition and suitability before mounting. A ring test is an additional pre-mounting check for applicable vitrified wheels: a light nonmetallic tap produces a sound that a trained person evaluates for indications of cracking. Wheel size, shape and composition limit where the test applies. A clear ring does not replace the other checks.

Truing restores the required wheel shape and concentric running. Dressing renews the cutting surface by removing unwanted material and exposing useful abrasive. An appropriate dressing operation may do both. Use the dresser and method specified for the wheel.

Loading means work material fills the wheel's spaces. Glazing means dull abrasive remains at the surface and rubs instead of cutting effectively. Either condition calls for correction, not simply more pressure.

Why a wheel can glaze, and where ring testing applies

Glazing depends on the wheel grade and operating conditions as well as the work material. Hard material alone does not diagnose it. Norton's ring-test guidance explains the method's application and limitations; follow the full manufacturer procedure before mounting.

Shape an HSS tool bit without overheating its edge

Grinding a high-speed steel tool bit creates the faces that meet at the cutting edge. Clearance behind the edge lets it cut without the adjacent tool face rubbing; rake influences chip flow. The required angles come from the intended tool and work material, not one universal sharpening angle.

Use light, controlled contact and check the shape frequently. Periodic dipping of a warm HSS bit in water can control temperature when the tool's instructions permit it. This is cooling during sharpening, not heat-treatment quenching; do not heat the bit severely and then plunge it into water.

Do not transfer that dipping method to a hot cemented-carbide tip. Sudden cooling can crack carbide. Use the specified dry method or a compatible continuous wet-grinding process. Intermittently quenching hot carbide is not equivalent to supplying coolant throughout the cut.

Carbide needs consistent temperature control

General Carbide: The Designer's Guide to Tungsten Carbide, page 50, explains thermal shock and the effects of interrupted coolant during grinding. Follow the tool manufacturer's cooling guidance for HSS as well; permission to cool a warm bit is not permission to quench an overheated one.

Aluminum and other soft, ductile metals can smear into and load a standard wheel intended for steel. Use equipment and abrasives specifically approved for the material. Changing from aluminum oxide to silicon carbide by itself does not establish that the whole setup is suitable.

Compare RPM ratings directly; calculate rim speed separately

The machine's spindle speed must not exceed the wheel's printed maximum operating RPM. A wheel's grade or grit marking is not that rating. Passing the RPM comparison is only one compatibility check; it does not approve the wheel's mounting, dimensions or application.

Rim speed is distance traveled at the wheel's outside diameter. With diameter D in inches and spindle speed N in revolutions per minute:

SFPM = π × D × N / 12, in surface feet per minute. The 12 converts inches to feet. Use diameter, not radius.

For an illustrative 7 in wheel at 1,750 RPM, π × 7 × 1,750 / 12 = 3,207 SFPM, rounded to the nearest whole foot per minute. This calculation is not a recommended operating speed. A smaller worn wheel has a lower rim speed at the same RPM; that does not authorize exceeding its marked maximum RPM.

See Feeds and Speeds for the same surface-speed relationship. Practice wheel speed Practice the RPM comparison