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Z94.12.5 Metal Machining

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SAE STEELS. A system of classification of steels and steel alloys, by their chemistry. It was developed by the Society of Automotive Engineers (SAE). It was later adopted and expanded by the American Iron and Steel Institute (AISI). Both plain-carbon and low-alloy steels are identified by a four-digit number. The first number indicates the major alloying elements and the second, a subgrouping of the major alloy system. The last two digits indicate the approximate carbon content of the metal.

SAWING. A basic machining process in which chips are produced by a succession of small cutting edges or teeth arranged in a narrow line on a saw blade. Saw blades are made in three basic configurations: hacksaw, band saw, and circular saw.

SCLEROSCOPE. An instrument for determining the relative hardness of materials by a drop-and-rebound method.

SCREW MACHINES. Small automatic turret lathes designed for bar stock and usually equipped with an automatic rod-feeding mechanism. They are single or multiple spindle machines. The Brown and Sharpe or the Swiss Automatic are two common types.

SELECTIVE ASSEMBLY. An assembly procedure where the parts are segregated into groups in order to affect particular matings of these component parts.

SHANK. The part of the drill or cutter by which it is held and driven.

SHAPING. A basic machining process where the tool is reciprocated, cutting only during the forward stroke, and the feed is intermittent between strokes.

SHAVING, GEAR. The most commonly used method for gear finishing. The gear is run at high speed in contact with the shaving tool which is a hardened accurately ground gear that contains a number of peripheral gashes or grooves, thus forming a series of  sharp cutting edges on each tooth. The gear and shaving cutter are run in mesh. The cutter removes very fine chips from the gear producing very accurate tooth profile.

SHEAR, IN METAL CUTTING. Chips are formed by a localized shear process which takes place over a very narrow region. The shear plane is the area over which the chip is removed from the parent metal. The shear plane is at an angle defined as the (shear angle) from the newly formed surface.

SHOT BLASTING. A method of abrasive cleaning to remove foreign materials from the formed workpiece. It employs blasting some type of abrasive, usually sand or steel grit or shot, which is impelled under high pressure against the surface to be cleaned.

SILICON CARBIDE. An abrasive made in the electric furnace from coke and silica SiC.

SINGLE-POINT TOOL. A tool with one cutting edge, usually used in turning operations.

SLOTTING. The production of a straight-sided groove in the work piece using a radial cutting tool action.

SNAG GRINDING. The nonprecision removal of unwanted material, such as sprues and gates in foundry operations by means of a grinding operation.

SPADE DRILLS. Usually made of a separate two edged drilling bit held in a solid supporting shank.

SUPPORTING SHANK. Widely used for making large holes.

SPARK DISCHARGE MACHINING. (See ELECTRIC DISCHARGE MACHINING.)

SPOT FACING. a drilling operation which is done to provide a smooth bearing area on an otherwise rough surface at the opening of a hole and normal to its axis. Counterboring tools are usually used for spot facing.

STANDARD HOLE TOLERANCING PRACTICE. The method of allocating dimensions and tolerances in which the minimal hole size is the nominal diameter. Tolerances and allowances are then applied to the shaft as determined from the class of fit.

STANDARD SHAFT TOLERANCING PRACTICE. The method of allocating dimensions and tolerances in which the maximum shaft size is the nominal diameter. Classes of fit is determined by varying the hole diameter.

STEADY REST. A device used to support long and slender workpieces during turning or grinding to reduce their deflection due to the force exerted by the cutting action.

STRADDLE MILLING. The production of more than one flat surface on the workpiece while employing more than one milling cutter.

STRAIN HARDENING. Many metals possess a unique property in that after undergoing some deformation, the metal possesses greater resistance to further plastic flow. In essence, metals become stronger when plastically deformed, a phenomenon known as strain hardening or work hardening.

SUPER FINISHING. A variation of the honing process which employs very light, controlled pressure with rapid short strokes and copious amounts of lubricant coolant flooded over the work surface to produce very fine surface finishes.

SURFACE FEET PER MINUTE (SFPM). The linear speed of the rotating tool or workpiece. Derived by multiplying the circumference in feet by revolutions per minute.

SURFACE GRINDING. Grinding a plane surface.

SURFACE PROFILE. (See PROFILE, SURFACE.)

SURFACE ROUGHNESS. (See ROUGHNESS.)

SWISS AUTOMATIC. (See SCREW MACHINES.)

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