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G-code programming

Programs written to operate NC machines with control systems that comply with the ANSI/EIA RS-274-D-1980 Standard. A program consists of a series of data blocks, each of which is treated as a unit by the controller and contains enough information for a complete command to be carried out by the machine.


Measure of the grinding performance defined as the volume of metal removed divided by the volume of grinding wheel worn away in the operation.


Condition whereby excessive friction between high spots results in localized welding with subsequent spalling and further roughening of the rubbing surface(s) of one or both of two mating parts.

gamma iron

Face-centered cubic form of pure iron. Each of eight atoms of gamma iron are located in the corner of a cube, and each of six atoms are located in the center of the cube’s face. Gamma iron is stable from 1,670º F (910º C) to 2,550º F (1,400º C).

gang cutting (milling, slitting)

Machining with several cutters mounted on a single arbor, generally for simultaneous cutting.

gantry robot

Robot positioned by means of an overhead supporting structure such as a crane or bridge-type support.

gear cutter

Cutter, such as a mill, broach and hob, designed for machining gears.

gear shaper

Machine that, in contrast to mills and hobbing machines, reciprocates the tool to cut the gear. See hobbing machine.

graphitic corrosion

Deterioration of gray cast iron in which the metallic constituents are selectively leached or converted to corrosion products leaving the graphite intact. The term graphitization is commonly used to identify this form of corrosion but is not recommended because of its use in metallurgy for the decomposition of carbide to graphite.

gray cast irons

Alloys of iron, carbon and silicon in which more carbon is present than can be retained in austenite. The carbon in excess of austenite solubility in iron precipitates as graphite flakes. Approximate composition of gray irons is: 2.5 to 4.0 percent carbon, 0.5 to 1.0 percent manganese, 1.0 to 3.0 percent silicon, 0.05 to 0.15 percent sulfur and 0.05 to 0.8 percent phosphorus. Some Society of Automotive Engineer grades are G-1800, G-2500, G-3000, G-3500 and G-4000.


Machining operation in which material is removed from the workpiece by a powered abrasive wheel, stone, belt, paste, sheet, compound, slurry, etc. Takes various forms: surface grinding (creates flat and/or squared surfaces); cylindrical grinding (for external cylindrical and tapered shapes, fillets, undercuts, etc.); centerless grinding; chamfering; thread and form grinding; tool and cutter grinding; offhand grinding; lapping and polishing (grinding with extremely fine grits to create ultrasmooth surfaces); honing; and disc grinding.

grinding machine

Powers a grinding wheel or other abrasive tool for the purpose of removing metal and finishing workpieces to close tolerances. Provides smooth, square, parallel and accurate workpiece surfaces. When ultrasmooth surfaces and finishes on the order of microns are required, lapping and honing machines (precision grinders that run abrasives with extremely fine, uniform grits) are used. In its “finishing” role, the grinder is perhaps the most widely used machine tool. Various styles are available: bench and pedestal grinders for sharpening lathe bits and drills; surface grinders for producing square, parallel, smooth and accurate parts; cylindrical and centerless grinders; center-hole grinders; form grinders; facemill and endmill grinders; gear-cutting grinders; jig grinders; abrasive belt (backstand, swing-frame, belt-roll) grinders; tool and cutter grinders for sharpening and resharpening cutting tools; carbide grinders; hand-held die grinders; and abrasive cutoff saws.

grinding ratio

Ratio of work material removed to grinding-wheel material lost.

grinding wheel

Wheel formed from abrasive material mixed in a suitable matrix. Takes a variety of shapes but falls into two basic categories: one that cuts on its periphery, as in reciprocating grinding, and one that cuts on its side or face, as in tool and cutter grinding.

grit size

Specified size of the abrasive particles in grinding wheels and other abrasive tools. Determines metal-removal capability and quality of finish.


Machining grooves and shallow channels. Example: grooving ball-bearing raceways. Typically performed by tools that are capable of light cuts at high feed rates. Imparts high-quality finish.


In cast iron, a permanent increase in dimensions resulting from repeated or prolonged heating at temperatures above 480° C due either to graphitizing of carbides or to oxidation.


Self-guided drill for producing deep holes with good accuracy and fine surface finish. Has coolant passages that deliver coolant to the tool/workpiece interface at high pressure.


Drilling process using a self-guiding tool to produce deep, precise holes. High-pressure coolant is fed to the cutting area, usually through the gundrill’s shank.