Glossary / Business

Machine Shop Glossary

Abrasive: (sandstone, emery, corundum, diamonds) or artificial (silicon carbide, aluminum oxide) material used
Abrasive Wheels: Wheels of a hard abrasive, such as Carborundum used for grinding.
Acetone: A colorless, flammable, volatile liquid used as a paint remover and as a solvent for oils and other
Acme Thread: A screw thread having a 29 degree included angle. Used largely for feed and adjusting screws on mach
Acute Angle: An angle that is less than 90 degrees.
Adapter: A tool holding device for fitting together various types or sizes of cutting tools to make them inte
Align: To adjust or set to a line or center.
Alloy: A substance with metallic properties, composed of two or more chemical elements of which at least on
Alloy Steel: A plain carbon steel to which another element, other than iron and carbon, has been added in a perce
Allthread: Steel or stainless steel rod threaded from end to end. It is available in a wide range of diameters
Aluminum: One of the chemical elements, a silvery, lightweight, easily worked metal that resists corrosion.
Angle Plate: A precision holding fixture made of cast iron, steel or granite. The two principal faces are at righ
Annealing: The controlled heating and cooling of a metal to remove stresses and to make it softer and easier to
Anvil: A heavy iron or steel block upon which metal is forged or hammered: also the fixed jaw on a micromet
Apron: That portion of a lathe carriage that contains the clutches, gears and levers for moving the carriag
Arbor: A shaft or spindle for holding cutting tools: most usually on a milling machine.
Arbor Press: A hand-operated machine tool designed for applying high pressure for the purpose of pressing togethe
Assembly: A unit of fitted parts that make up a mechanism or machine, such as the headstock assemble of a lath
Austenite: One of the basic steel microstructures wherein carbon is dissolved in iron.Austenite forms at elevat
Automatic Stop: A device which may be attached to any of several parts of a machine tool to stop the operation of th
Axis: The line, real or imaginary, passing through the center of an object about which it could rotate: a
Babbitt: An antifriction metal alloy used for bearing inserts: made of tin, antimony, lead and copper.
Back Gears: Gears fitted to a machine to increase the number of spindle speeds obtainable with a cone or step pu
Back Rake: The angular surface ground back from the cutting edge of cutting tools. On lathe cutting tools the r
Backlash: The lost motion or looseness (play) between the faces of meshing gears or threads.
Bandsaw: A power saw the blade of which is a continuous, narrow, steel band having teeth on one edge and pass
Bar Stock: Metal bars of various lengths, made in flat, hexagon, octagon, round and square shapes from which pa
Bastard: Threads, parts, tools and sizes that are not standard, such as bastard nuts, bastard plugs, bastard
Bearing: Rollers and balls placed between moving parts to reduce friction and wear.
Bed: One of the principal parts of a machine tool, having accurately machined ways or bearing surfaces fo
Bell Mouth: The flaring or tapering of a machined hole, usually made at the entrance end because of misalignment
Bench Grinder: A small grinding machine for shaping and sharpening the cutting edges of tools.
Bevel: Any surface that is not at right angles to another surface. Also, the name given a tool used for mea
Bit - Tool (Cutter): A hardened steel bar or plate that is shaped according to the operation to be performed and the mate
Blind Hole: A hole made in a workpiece that does not pass through it.
Body-Centered Cubic (BCC): One of the common types of unit cells described as a cube with an atom at each of the eight corners
Bore: To enlarge and finish the surface of a cylindrical hole by the action of a rotating boring bar (cutt
Boring Bar: A combination tool holder and shank.
Boring Tool: A cutting tool in which the tool bit the boring bar and, in some cases, the tool holder are incorpor
Boss: A projection or an enlarged section of a casting through which a hole may be machined.
Brass: A nonferrous alloy consisting essentially of copper and zinc.
Brazing: A group of welding processes that produces coalescence of materials by heating them to the brazing t
Brine: A saltwater solution for quenching or cooling when heat treating steel.
Brinell Hardness: A method of testing the hardness of a metal by controlled pressure of a hardened steel ball of a giv
Brinell Hardness Test: A common testing method using a ball penetrator. The diameter of the indentation is converted to uni
Broach: A long, tapered cutting tool with serration's which, when forced through a hole or across a surface,
Bronze: A nonferrous alloy consisting essentially of copper and tin.
Buff: To polish to a smooth finish of high luster with a cloth or fabric wheel to which a compound has bee
Burnishing: The process of finishing a metal surface by contact with another harder metal to improve it. To make
Burr: The sharp edge left on metal after cutting or punching: also, a rotary cutting tool designed to be a
Bushing: A sleeve or a lining for a bearing or a drill jig to guard against wear.
Caliper: A device used to measure inside or outside dimensions.
Cam: A device for converting regular rotary motion to irregular rotary or reciprocating motion. Sometimes
Capillary Action: The force by which liquid in contact with a solid is distributed between closely fitted faying surfa
Carbide Tool Bits: Lathe cutting tools to which carbide tip inserts have been brazed, to provide cutting action on hard
Carbon: A nonmetallic chemical element that occurs in many inorganic and all organic compounds. Carbon is fo
Carbon Steel: A broad term applied to tool steel other than high-speed or alloy steel.
Carriage: A principal part of a lathe that carries the cutting tool and consists of the saddle, compound rest
Case Hardening: A heat treating process, basically carbonizing that makes the surface layer or case of steel substan
Cast Iron: A family of alloys, containing more than 2% carbon and between 1 and 3% silicon. Cast irons are not
Casting: A part made by pouring molten metal into a mold.
Castle Nut: A nut with grooves cut entirely across the top face for the purpose of resisting loosening with vibr
Center: A point or axis around which anything revolves or rotates. In the lathe one of the parts upon which
Center Drill: A combination drill and countersink.
Center Drill: A combined countersink and drill used to prepare work for mounting centers.
Center Gage: A small, flat gage having 60º angles that is used for grinding and setting the thread cutting tools
Center Head: A part of a combination square set that is used to find the center of or to bisect a round or square
Center Punch: A pointed hand tool made of hardened steel and shaped somewhat like a pencil.
Center Punch: A solid punch with a point used to get a drill started in the proper location and often used after t
Chamfer: The bevel or angular surface cut on the edge or a corner of a machined part.
Chasing Threads: Cutting threads in a lathe or screw machine.
Chatter: The vibrations caused between the work and the cutting tool which leave distinctive tool marks on th
Chip Breaker: A small groove ground back of the cutting edge on the top of a cutting tool to keep the chips short.
Chipping: The process of cutting metal with a cold chisel and hammer.
Chisel: Any one of a variety of small hand cutting tools, generally wedge-shaped.
Chromium: A lustrous, hard, brittle, steel-gray metallic element used to harden steel alloys, in production of
Chuck: A device on a machine tool to hold the workpiece or a cutting tool.
Chuck (Independent Jaw): A chuck, each of whose jaws (usually four) is adjusted with a screw action independently of the othe
Chuck (Universal): A chuck whose jaws are so arranged that they are all moved together at the same rate by a special wr
Clearance: The distance or angle by which one objector surface clears another.
Clearance Angle: The angle between the rear surface of a cutting tool and the surface of the work at the point of con
Climb Milling: A method of milling in which the work table moves in the same direction as the direction of rotation
Climb Milling: See climb milling: see face milling.
Coefficient Of Thermal Expansion: The increase in length per unit length for each degree a metal is heated.
Cohesion: Cohesion is the result of a perfect fusion and penetration when the molecules of the parent material
Cold Work: Cold working refers to forming, bending, or hammering a metal well below the melting point. Cold wor
Cold-Rolled Steel: Steel that has been rolled to accurate size and smooth finish when made. In contrast, hot-rolled ste
Collet: A precision work-holding chuck which centers finished round stock automatically when tightened. Spec
Combination Square: A drafting and layout tool combining a square, a level, a protractor and a center head.
Compound (Rest): The part of a lathe set on the carriage that carries the tool post and holder. It is designed to swi
Concave: A curved depression in the surface of an object.
Concentric: Accurately centered or having a common center.
Contour: The outline of an object.
Convex: The curved surface of a cylinder, as a sphere when viewed from without.
Coolant: A common term given to the numerous cutting fluids or compounds used with cutting tools to increase
Corrosion: Oxidation (rusting) or similar chemical change in metals.
Counterbore: To enlarge the top part of a hole to a specific size, as for the head of a sockethead or cap-screw.
Countersink: To enlarge the top part of a hole at an angle for a flat-head screw. Also, the tool that is used.
Cross Feed: The feed that operates across the axis of the workpiece or at right angles to the main or principal
Cross Section: A view showing an internal structure as it would be revealed by cutting through the piece in any pla
Crucible Steel: A high-grade tool steel made by melting selected materials in a crucible.
Cutting Fluid: A liquid used to cool and lubricate the cutting to improve the work surface finish.
Cutting Speed: The surface speed of the workpiece in a lathe or a rotating cutter, commonly expressed in feet per m
Cutting Tool: A hardened piece of metal (tool steel) that is machined and ground so that it has the shape and cutt
Dead Center: A center that does not rotate: commonly found on the tailstock of a lathe. Also, an expression for t
Dead Center: See center, dead.
Dead Smooth: The term applied to the finest cut of a file.
Deburr: To remove sharp edges.
Depth Micrometer: A micrometer in which the spindle projects through a flat, accurately machined bar used to measure t
Die: A tool used to form or stamp out metal parts', also, a tool used to cut external threads.
Die Stock: The frame and two handles (bars) which hold the dies (chasers) used for cutting (chasing) external s
Dividing Head: A machine tool holding fixture which positions the work for accurately spacing holes slots flutes an
Dog: A clamping device (lathe dog) used to drive work being machined between centers. Also, a part projec
Dovetail: A two-part slide bearing assembly used in machine tool construction for the precise alignment and sm
Dowel: A pin fitted or keyed in two adjacent parts to accurately align the parts when assembling them.
Down Feed: A seldom used method of feeding work into milling cutters. The work is fed in the same direction as
Draw: See tempering.
Dressing: The act of removing the glaze and dulled abrasives from the face of a grinding wheel to make it clea
Drift: A tapered, flat steel used to remove drills and other tapered shank tools from spindles, sockets, or
Drill Bushing: A hardened steel guide inserted in jigs, fixtures or templates for the purpose of providing a guide
Drill Chuck: A device used to grip drills and attach them to a rotating spindle.
Drill Jig: A jig which holds parts or units of a structure and by means of bushings, guides the drill so that t
Drill Press: A drilling machine with a counterbalanced spindle which makes it possible for the operator to contro
Drill Rod: A term given to an annealed and polished high carbon tool steel rod usually round and centerless gro
Drill Sleeve: An adapter with an internal and external taper which fits tapered shank tools such as drills or ream
Drill Socket: An adapter similar to a sleeve except that it is made to adapt a larger taperedshank tool to a small
Drive Fit: One of several classes of fits in which parts are assembled by pressing or forcing one part into ano
Ductility: The property of a metal that permits it to be drawn, rolled, or hammered without fracturing or break
Eccentric: A circle not having a geometric center. Also, a device such as a crankshaft or a cam for converting
Elastic Limit: The greatest stress the material can withstand without permanent elongation when all load has been r
Element: Matter which cannot be broken up into simpler substances by chemical action, that is, whose molecule
Emery: A natural abrasive used for grinding or polishing. It is being largely replaced by artificial abrasi
Emulsion: A coolant formed by mixing soluble oils or compounds with water.
Face: To machine a flat surface, as in the end of a shaft in the lathe. The operation is known as facing.
Face Milling: Milling a large flat surface with a milling cutter that operates in a plane that is at right angles
Face-Centered Cubic (FCC): One of the common types of unit cells in which atoms are located on each corner and the center of ea
Faceplate: A large circular plate with slots and holes for mounting the workpiece to be machined. It is attache
Facing: The process of making a flat or smooth surface (usually the end) on a piece of stock
Fatigue: The effect on certain materials, especially metals, undergoing repeated stresses.
Fatigue Failure: The sudden and complete breakage of a part as a result of the repeated application of a load. Fatigu
Fatigue Strength: Ability of a material to withstand repeated loading.
Feed: The rate of travel of a cutting tool across or into the work, expressed in inches per minute, in inc
Feed Mechanism: The mechanism, often automatic, which controls the advancing movement (feed) of the cutting tools us
Feeler Gage: A gage consisting of a group of very thin blades, each of which is accurately ground to a specific t
Female Part: A concave piece of equipment which receives a mating male (convex) part.
Ferrous: A metal alloy in which iron is the major ingredient.
Filler Material: The material, metal, or alloy to be added in making a welded, brazed, or soldered joint.
Finish Machining: Machining a surface to give it the desired finish.
Fishtail: A common name for the center gage. It is used to set thread cutting tools and has scales on it for d
Fit: The relation between mating or matching parts, that is, the amount of, or lack of play between them.
Fixture: A production work-holding device used for machining duplicate workpieces. Although the term is used
Flange: A relatively thin rim around a part.
Flute: The groove in a cutting tool which provides a cutting edge and a space for the chips to escape and p
Flycutter: A single-point cutter mounted on a bar in a flycutter holder or a flycutter arborused for special ap
Follower Rest: A support for long, slender work turned in the lathe. It is mounted on the carriage, travels close t
Footstock: Part of an indexing, attachment which has a center and serves the same purpose as the tail stock of
Force Fit: A fitting which one part is forced of pressed into another to form a single unit. There are differen
Forge: To form or shape heated metal by hammering. Also, the name of the unit used for heating metal, as th
Formed Cutters: Milling cutters, which will produce shaped surfaces with a single cut are so designed that they may
Forming Tool: Tool ground to a desired shape to reproduce this shape on the workpiece.
Fpm: Feet per minute of workpiece.
Free Cutting Steel: Bar stock containing a high percentage of sulfur making it very easy to machine.
Free Fit: A class of fit intended for use where accuracy is not essential or where large temperature variation
Fuel Gas: A gas such as acetylene, natural gas, hydrogen, propane, stabilized methylacetylene propadiene and o
Fulcrum: The point or support on which a lever turns.
Fusion: The joining of base material, with or without filler material, by melting them together.
Gage: Any one of a large variety of devices for measuring or checking the dimensions of objects.
Gang Milling: A milling setup where a number of cutters are arranged on an arbor so that several surfaces can be m
Gib: A tapered strip of metal placed between the bearing surface of two machine parts to ensure a precisi
Gtaw: The Gas Tungsten Arc Welding process: non-standard terms are Heliarc™ and TIG (tungsten inert gas)
Hacksaw: A metal blade of hardened steel having small, close teeth on one edge. It is held under tension in a
Half Center: A dead center that has a portion of the 60 degree cone cut away.
Half-Nut: A lever-operated mechanism that resembles a split nut that can be closed on the leadscrew of a lathe
Handwheel: Any adjusting or feeding mechanism shaped like a wheel and operated by hand.
Hardening: A heat-treating process for steel which increases its hardness and tensile strength and reduces its
Hardness Tests: Tests to measure the hardness of metals.
Headstock: The fixed or stationary end of a lathe or similar machine tool.
Heat Treatment: The process of heating and cooling a solid metal or alloy to obtain certain desired properties or ch
Helical Gear: A gear with teeth cut at some angle other than at a right angle across the face of the gear, thus pe
Helix: A path formed as a point advances uniformly around a cylinder, as the thread on a screw or the flute
Helix Angle: The angle between the direction of the threads around a screw and a line running at a right angle to
Hex: A term used for anything shaped like a hexagon.
Hexagonal Close Packed (HCP): A unit cell in which two hexagons (six-sided shapes) form the top and bottom of the prism. An atom i
High-Speed Steel (HSS): An alloy steel commonly used for cutting tools because of its ability to remove metal at a much fast
Hob: A cylindrical cutting tool shaped like a worm thread and used in industry to cut gears.
Hobbing: The operation of cutting gears with a hob.
Hog: To remove in excess of what is considered normal, sometimes causing accidents or tool breakage: also
Hole Saw: A cutting tool used to cut a circular groove into solid material.
Honing: The process of finishing ground surfaces to a high degree of accuracy and smoothness with abrasive b
Hot-Rolled Steel: Steel which is rolled to finished size while hot. Identified by a dark oxide scale left on the surfa
Hydrogen: The lightest chemical element, colorless, odorless and tasteless. It is found in combination with ot
Idler: A gear or gears placed between two other gears to transfer motion from one gear to the other gear wi
Impact Strength: The ability of a material to resist shock, dependent on both strength and ductility of the material.
Independent Chuck: A chuck in which each jaw may be moved independently of the others.
Index Plate: A metal disk or plate punched with many holes arranged in a series of rings, one outside the other e
Indexing: The process of positioning a workpiece for machining it into equal spaces, dimensions or angles usin
Indexing Fixture: A complete indexing unit composed of a dividing head and rootstock. (See dividing head.).
Indicating Gage: A gage consisting of a dial, commonly graduated (marked) in thousandths of an inch, to which is fast
Indicator: A precision instrument which shows variations of thousandths of an inch or less when testing the tru
Inserted-Tooth Cutter: A milling cutter designed with replaceable cutting tooth inserts to save the expense of a new cutter
Iron Carbide: A binary compound of carbon and iron: it becomes the strengthening constituent in steel.
Iron-Carbon Phase Diagram: A graphical means of identifying different structures of steel and percentages of carbon occurring i
Jarno: A standard taper having 0.600-inch taper per foot used on some machine tools.
Jig: A device that holds the workpiece in place and guides the cutting tool during the cutting operation.
Johannson Blocks (Jo Blocks): Common term for the precision gage blocks used and accepted as dimensional standards by machinists,
Joint Clearance: The distance between the faying surfaces of a joint in brazing or soldering.
Kerf: The width of a cut produced during a cutting process.
Key: One of the several types of small metal objects designed to fit mating slots in a shaft and the hub
Keyseat: A recessed groove (slot) machined into a shaft or a part going on the shaft (usually a wheel or gear
Knee: That part of a column of a knee-type milling machine which carries the saddle and the table and prov
Knurl: A decorative gripping surface of straight-line or diagonal design made by uniformly serrated rolls c
Knurling: The process of finishing a part by scoring (pressing) patterns on the surface of the work.
Land: That surface on the periphery of a rotary cutting tool, such as a milling cutter, drill tap, or ream
Lap: A tool made of soft metal and charged with fine abrasives for precision finishing of metal surfaces.
Lard Oil: A cutting oil made from animal fats usually mixed with mineral oils to reduce its cost and improve i
Layout: To locate and scribe on blank stock the shape and size dimensions required to machine or form the pa
Lead: The distance a thread will advance along its axis in one complete revolution. Also, a heavy, soft, m
Leadscrew: The long, precision screw located in front of the lathe bed geared to the spindle and used for cutti
Leveling Jack: Small jacks (usually screw jacks) for leveling and holding work on planner beds and similar places.
Lh: Left hand.
Limits: The smallest and largest dimension which are tolerable (allowed).
Line Reaming: The process of reaming two or more holes to bring them into very accurate alignment.
Lip Of A Drill: The sharp cutting edge on the end of a twist drill.
Liquidus: The lowest temperature at which a metal or an alloy is completely liquid.
Live Center: See center, live.
Live Center: A center that revolves with the work. Generally this is the headstock center: however, the ball bear
Loading: A condition caused by grinding the wrong material with a grinding wheel or using too heavy a grindin
Machinability: The degree of difficulty with which a metal may be machined: may be found in appropriate handbooks.
Machine Tool: A power-driven machine designed to bore, cut, drill, or grind metal or other materials.
Machinist: A person who is skilled in the operation of machine tools. He must be able to plan his own procedure
Magnesium: A lightweight, ductile metal similar to but lighter than aluminum.
Magnetic Chuck: A flat smooth-surfaced work holding device which operates by magnetism to hold ferrous metal workpie
Malleable: Capable of being extended or shaped by hammering or rolling.
Mandrel: A precision-made tapered shaft to support work for machining between centers.
Manganese: A gray-white nonmagnetic metallic element resembling iron, except it is harder and more brittle. Man
Martensite: A very hard, brittle microstructure of steel produced when steel is rapidly quenched after being tra
Medium Steel: Refer to carbon steel.
Mesh: To engage, as the teeth between two gears.
Metal: A class of chemical elements that are good conductors of heat and electricity, usually malleable, du
Metallic Bond: The principal atomic bond that holds metals together.
Metallurgy: The science explaining the properties, behavior and internal structure of metals.
Methylacetylene Propadiene: A family of alternative fuel gases that are mixtures of two or more gases (propane, butane, butadien
Microstructure: A term use to describe the structure of metals. Visual examination of etched metal surfaces and frac
Mike: A term used for micrometer, or to measure with a micrometer.
Mild Steel: Refer to carbon steel.
Mill: A milling machine: also, the act of performing an operation on the milling machine.
Milling Cutter: A cutting tool, generally cylindrical in shape used on a milling machine and operated essentially li
Minor Diameter: The smallest diameter of a screw thread. Also known as the root diameter.
Modulus Of Elasticity: The ratio of stress to strain in material: also referred to as Young’s modulus.
Molybdenum: A hard, silver-white metal, a significant alloying element in producing engineering steels, corrosio
Monel: A high tensile strength Ni-Cu alloy that exhibits high fatigue resistance in salt water, corrosive a
Morse Taper: A self-holding standard taper largely used on small cutting tools such as drills, end mills and ream
Multiple-Thread Screw: A screw made of two or more threads to provide an increased lead with a specified pitch.
Music Wire: A high-quality steel wire used for making springs. Also called piano wire.
Necking: Machining a groove or undercut in a shaft to permit mating parts to be screwed tightly against a sho
Nickel: An alloying element which increases the strength, toughness and wear and corrosion resistance of ste
Nitrogen: A gaseous element that occurs freely in nature and constitutes about 78% of earth’s atmosphere. Co
Nominal Pipe Size (NPS): The size of pipe is identified by its nominal pipe size. For pipes between 1/8- and 12-inches nomina
Noncorrosive Flux: A soldering flux that in either its original or residual form does not chemically attack the base me
Nonferrous: Metal containing no iron, such as brass and aluminum.
Normalizing: The process of heating a metal above a critical temperature and allowing it to cool slowly under roo
Off Center: Not centered: offset, eccentric, or inaccurate.
Oil Hardening: The process of quenching in oil when heat treating alloy steel to bring out certain qualities.
Oilstones: Molded abrasives in various shapes used to hand-sharpen cutting tools.
Oxidizing Flame: An oxyfuel flame in which there is an excess of oxygen, resulting in an oxygen-rich zone extending a
Oxygen: A colorless, odorless, tasteless, gaseous chemical element, the most abundant of all elements. Oxyge
Pack Hardening: A heat-treating process in which the workpiece is packed into a metal box together with charcoal, ch
Parallels: Hardened steel bars accurately ground to size and ordinarily made in pairs in many different sizes t
Parting: The operation of cutting off a piece from a part held in the chuck of a lathe.
Pattern: Wood, metal, paper, or plastic sheet material that replicates the shape of a part. Patterns are used
Peen: To draw, bend or flatten, also, the formed side of a hammer opposite the face.
Phase Transition: Iron phase transitions are at room temperature to 1,670°F (910°C) iron is body-center cubic, 1670
Phase Transitions: When metals or metal alloys go from solid to liquid or the reverse, this is a
Phosphoric Acid: The acid, H3PO4, widely used in industrial metal cleaning.
Phosphorous: A highly reactive, toxic, nonmetallic element used in steel, glass and pyrotechnics. It is almost al
Pilot: A guide at the end of a counterbore which keeps it aligned with the hole.
Pilot Hole: A starting hole for large drills to serve as a guide, reduce the resistance and aid in maintaining t
Pin Fixture: A tool for bending wire, bar, or rod into a curve or series of curves.
Pinning: A term used to describe the condition of a file clogged with metal filings causing it to scratch the
Pitch: The distance from any point on a thread to the corresponding point on the adjacent thread, measured
Pitch Diameter: The diameter of a thread at an imaginary point where the width of the groove and the with of the thr
Pitch Line: An imaginary line which passes through threads at such points that the length of the part of the lin
Plain Cutter: A milling cutter with cutting teeth on the periphery (circumference) only.
Play: The looseness of fit (slack) between two pieces.
Plug Weld: A weld made in a circular hole in one member of a joint fusing that member to another member.
Powder Coating: A durable, weather-proof, polymer coating for metals applied in a spray and then cured in an oven.
Prick Punch: A solid punch with a sharp point, used to mark centers or other locations on metal.
Proportional Limit: The greatest stress a material can withstand without deviation from the straight-line proportionalit
Protective Atmosphere: A gas or vacuum envelope surrounding the workpieces, used to prevent or reduce the formation of oxid
Pyrometer: A device for measuring the high temperatures in a heat-treating furnace.
Quenching: The sudden cooling of heated metal by immersion in water, oil, or other liquid. The purpose of quenc
Quick Return: A mechanism on some machine tools that provides rapid movement of the ram or table on the return or
Rack: An array of gears spaced on a straight bar.
Radial: In a direction directly outward from the center of a circle or sphere or from the axis of a cylinder
Radius: The distance from the center of a circle to its circumference (outside).
Radius Gage: Any one of a number of small, flat, standard-shaped metal leafs or blades used for checking the accu
Rake: That surface of a cutting tool against which the chips bear while being severed. If this surface is
Ram: That part of a shaper which moves back and forth and carries the tool head assembly.
Rapid Traverse: A lever-controlled, power-operated feature of some machines that permits the rapid movement of the w
Recess: An internal groove. See undercut.
Relief: A term for clearance or clearance angle.
Residual Stress: Stress present in a joint member or material that is free of external forces or thermal gradients.
Rockwell Hardness Test: The most common hardness testing method. This procedure uses a minor load to prevent surface irregul
Rough Machining: Removing excess stock (material) with a machine tool thus shaping it in preparation for finish machi
Roughing: The fast removal of stock to reduce a workpiece to approximate dimensions, leaving only enough mater
Running Fit: A class of fit intended for use on machinery with moderate speeds, where accurate location and minim
Sae: The Society of Automotive Engineers.
Scale: The rough surface on hot finished steel and castings. Also, a shop term for steel rules.
Scraper: A hardened steel hand tool used to scrape surfaces very smooth by removing minute amounts of metal.
Screw Pitch Gage: A gage consisting of a group of thin blades used for checking the number of screw threads per unit o
Scribe: A steel rod 8 to 12-inches long and about 3/16 inches in diameter. It has a long, slender, hardened
Sector: A device that has two radial, beveled arms which can be set to include any number of holes on the in
Set: The bend or offset of a saw tooth to provide a clearance for the blade while cutting. Also, the perm
Set Screw: A plain screw used principally for locking adjustable parts in position.
Setup: The preparation of a machine tool to complete a specific operation. It includes mounting the workpie
Sf: Standard form.
Shank: That part of a tool or similar object which connects the principal operating part to the handle, soc
Shear Strength: The characteristic of a material to resist shear forces.
Shims: Very thin sheets of metal made in precise thickness and used between parts to obtain desired spacing
Shoulder: A term for the step made between two machined surfaces.
Shrink Fit: A class of fit made when the outer member is expanded by heating to fit over a shaft and then contra
Side Cutter: A milling cutter that has cutting teeth on the side as well as on the periphery or circumference.
Side Rake: That surface which slopes to the side of the cutting edge. It may be positive or negative and is com
Sine Bar: A precision instrument for laying out, setting, testing and otherwise dealing with angular work.
Slabbing Cutter: A wide, plain milling cutter having helical teeth. Used for producing large, flat surfaces.
Slitting Saw: A narrow milling cutter designed for cutoff operations or for cutting narrow slots.
Slotter: An attachment which operates with a reciprocating motion. Used for machining internal slots and surf
Soft Hammer: A hammer made of brass, copper, lead or plastic to a non-marring finished surfaces on machines or wo
Soft Jaws: Plastic, leather, lead, or aluminum covers on the jaws of a vise or pliers used to prevent marking a
Solder: The metal or alloy used as a filler metal in soldering, which has a liquidus not exceeding 840ºF (4
Solid Square: A very accurate try square in which a steel blade is set firmly into a solid, rectangular-shaped han
Spheroidizing: A stress relieving method of long-term heating of high-carbon steel at or near the lower transformat
Spindle: A rotating device widely used in machine tools such as lathes, milling machines, drill presses and s
Spindle Speed: The RPM at which a machine is set.
Spot Facing: Finishing a bearing surface around the top of a hole.
Spring Dividers: Dividers whose legs are held together at the hinged end by the pressure of a C-shaped spring.
Spur Gear: A gear with teeth parallel to the axis of the shaft on which it is mounted.
Square Surface: A surface at a right angle with another surface.
Square Threads: A thread having a depth, width and space between threads that are equal. It is used on heavy jack sc
Steady Rest: A support that is clamped to the bed of a lathe used when machining a long workpiece. Sometimes call
Steel: A material composed primarily of iron, less than 2% carbon and (in an alloy steel) small
Step Block: A fixture designed like a series step to provide support at various heights required for setups.
Stock: A term for the materials used to make parts in a machine tool. Also, the die stock used for threadin
Stop: A device attached to a machine tool to limit the travel of the worktable and sometimes the work head
Straddle Milling: A milling setup where two side milling cutters are spaced on an arbor to machine two parallel surfac
Surface Grinding: The process of grinding flat surfaces on a surface grinding machine. With special setups, angular an
Surface Plate: An accurately machined and scraped flat metal piece (usually of cast iron) used to check the flatnes
Swing: The dimension of a lathe determined by the maximum diameter of the work that can be rotated over the
T-Bolt: Term for the bolts inserted in the T-slots of a worktable to fasten the workpiece or work-holding de
T-Slot: The slots made in the tables of machine tools for the square-head bolts used to clamp the workpiece,
Tailstock: That part of a machine tool, such as a lathe or cylindrical grinder which supports the end of a work
Tang: The flat on the shank of a cutting tool, such as a drill, reamer or end mill, that fits a slot in th
Tap: A tool used to cut threads on the inside of a round hole.
Taper: A uniform increase or decrease in the size or diameter of a workpiece.
Tapping: The process of cutting screw threads in a round hole with a tap.
Telescoping Gage: A T-shaped gage used to measure the diameter or width of holes.
Tempering: A heat-treating process to relieve the stresses produced when hardening and to impart certain qualit
Template: A pattern or guide for laying out or machining to a specific shape or form.
Tensile Strength: The resistance to breaking exhibited by a material when subjected to a pulling stress. Measured in l
Thermal Expansion: The expansion of materials caused by heat input.
Thermal Stress Relieving: A process of relieving stresses by uniform heating of a structure or a portion of a structure, follo
Thread: A helical projection of uniform section on the internal or external surface of cylinder or cone. Als
Thread Axis: A line running lengthwise through the center of the screw.
Thread Crest: The top surface joining the two sides of a thread.
Thread Depth: The distance between the crest and the root of a thread.
Thread Micrometer: A micrometer in which the spindle is ground to a point having a conical angle of 60 degrees. The anv
Thread Pitch: The distance from a point on one screw thread to a corresponding point on the next thread.
Thread Pitch Diameter: The diameter of a screw thread measured from the thread pitch line on one side to the thread pitch l
Thread Root: The bottom surface joining the sides of two adjacent threads.
Tool Steel: A general classification for high-carbon steel that can be heat treated to a hardness required for m
Torsion: The stress produced in a body, such as a rod or wire, by turning or twisting one end while the other
Traverse: One movement across the surface of the work being machined.
Truing: The act of centering or aligning a workpiece or cutting tool so that an operation may be performed a
Tumbler Gears: A pair of small lever-mounted gears on a lathe used to engage or to change the direction of the lead
Twist Drill: A commonly used metal-cutting drill, usually made with two flutes running around the body.
Two-Lip End Mill: An end-milling cutter designed with teeth that cut to the center so that it may be used to feed into
Ultimate Tensile Strength (UTS): The maximum tensile stress a material placed in tension can bear without breaking.
Universal Milling Machine: A milling machine with a worktable that can be swiveled for milling helical work. It is always suppl
Universal Vise: A vise designed for holding work at a double or compound angle. Also called a toolmakers’ vise.
Volt: A unit of electrical force or potential.
Ways: The flat or V-shaped bearing surfaces on a machining tool that guide and align the parts which they
Wheel Dresser: A tool or device for dressing or truing a grinding wheel.
Work Hardening: Also called cold working: the process of forming, bending, or hammering a metal well below the melti
Yield Strength: The stress at the uppermost point on the straight-line portion of the stressstrain curve. Stress imp