Tamil Nadu HSE First Year Basic Mechanical Engineering key terms

The property of a metal that lets it be hammered or rolled into thin sheets without cracking. It is the reason metals such as copper and aluminium can be beaten flat in smithy work.

The ability of a metal to be drawn out into a long wire without breaking. It is measured by how much a specimen stretches before it fractures in a tensile test.

The capacity of a material to absorb energy and deform plastically before it fractures. A tough metal resists sudden shock loads better than a hard but brittle one.

The tendency of a material to fracture with little or no plastic deformation. Cast iron is a classic brittle material and fails suddenly without warning when overloaded.

The resistance of a surface to scratching, indentation or wear. It is commonly tested by pressing a hardened ball or diamond into the metal and measuring the impression.

A heat treatment in which metal is heated and then cooled slowly to soften it, remove internal stresses and refine grain structure. It makes cold-worked metal easier to cut and bend.

Reheating hardened steel to a moderate temperature and cooling it to reduce brittleness while keeping most of the hardness. The higher the tempering temperature, the tougher but softer the steel.

An iron-carbon alloy containing roughly two to four percent carbon, made by remelting pig iron in a cupola. It is cheap, fluid when molten and good for machine beds and covers.

A low-carbon steel with about 0.15 to 0.3 percent carbon, widely used in workshop practice. It is soft, weldable, cheap and suitable for bolts, brackets and general fabrication.

Steel containing roughly 0.6 to 1.5 percent carbon, which can be hardened by heat treatment. It is used for cutting tools such as chisels, files and drills.

A measuring instrument with a main scale and a sliding vernier scale that reads to about 0.02 mm. It measures outside, inside and depth dimensions with its jaws and depth rod.

The smallest measurement an instrument can read reliably. For a vernier caliper it equals one main scale division divided by the number of vernier divisions.

A precision instrument using a calibrated screw and thimble to measure small thicknesses and diameters, typically to 0.01 mm. The spindle advances one pitch per revolution of the thimble.

A checking tool with a hardened steel blade set at exactly ninety degrees in a stock. It is used to test squareness of corners and to mark lines across a workpiece.

A sharp-pointed hardened steel rod used to scratch layout lines on metal surfaces. It is held like a pencil and guided along a steel rule or try square.

A small hardened steel tool struck with a hammer to mark centres or dot positions for drilling. A centre punch has a sharp point; a dot punch has a blunter angle.

A clamping device fixed to the workbench, with two jaws opened by a screw, to hold work firmly during filing, sawing or chiselling. Soft jaw caps protect finished surfaces.

A bench operation in which a file is pushed across the workpiece to remove metal and produce a smooth surface or accurate size. The cut is made on the forward stroke only.

A hand saw with a thin, fine-toothed blade held under tension in a frame, used to cut metal bar and pipe. The blade cuts on the forward stroke and must have at least three teeth in contact.

A wedge-shaped hardened steel cutting tool struck by a hammer to shear off metal or wood. In fitting, the cold chisel removes rivet heads and chips welds.

A matched pair of threading tools: the tap cuts an internal thread in a drilled hole, while the die cuts an external thread on a rod. Tapping needs a suitable tapping drill size.

The operation of producing a round hole in a workpiece by rotating a cutting tool called a drill. The drill is fed axially while the work or the spindle rotates.

A machine tool that rotates the workpiece against a single-point cutting tool to produce cylindrical surfaces. Operations include turning, facing, drilling and thread cutting.

The rate at which the cutting edge of a tool moves relative to the work surface, usually expressed in metres per minute. It depends on the material of both tool and workpiece.

The distance the cutting tool advances into the work per revolution or per stroke. A coarse feed removes metal quickly but leaves a rougher surface finish.

A joining process in which a filler metal melting below about 450 degrees Celsius wets and bonds the workpieces without melting them. Common fillers are tin-lead alloys with a flux.

A joining process using a non-ferrous filler such as a copper-zinc alloy that melts above soldering range but below the melting point of the parent metal. It gives a stronger joint than soldering.

A joining process that fuses the edges of two parts, usually by heat, with or without a filler rod. It produces a continuous, strong joint and is common in fabrication work.

A fusion welding process in which an electric arc between an electrode and the work generates the heat. The electrode may be consumable and coated to shield the molten pool.

A vertical shaft furnace used in foundries to melt pig iron and scrap for producing cast iron. Alternate layers of coke, flux and metal charge are fed from the top.

A replica of the part to be cast, slightly larger than the finished casting to allow for shrinkage. It forms the cavity in the mould sand and may be made of wood or metal.

The process of pouring molten metal into a mould cavity and letting it solidify to take the cavity's shape. It allows complex shapes to be made in one piece.

A standard number indicating the thickness of sheet metal; a higher gauge number means thinner sheet. Standard wire gauge tables convert the number to millimetres.

A permanent fastening method in which a ductile metal pin passes through holes in two parts and its tail is hammered into a head. It is widely used in sheet metal and structural work.

A sheet metal forming operation that folds the metal along a straight line, usually over a stake or in a folding machine. Allowance must be made for the material stretched at the bend.

The methods of connecting timber pieces, such as lap, mortise-and-tenon, dovetail and dowel joints. The choice depends on the strength, appearance and direction of load required.

A strong carpentry joint in which a projecting tenon on one member fits into a rectangular mortise cut in the other. It resists both pulling apart and twisting of the frame.

The craft of shaping timber with saws, planes, chisels and boring tools to make joints and finished articles. Grain direction governs how each tool should be used.

The shaping of hot metal by hammering, pressing or upsetting so that the grain flows with the shape. It produces parts that are stronger than equivalent castings.

A heavy block of hardened steel on which hot metal is hammered in smithy work. Its face is used for flat work, the horn for bending curves and the hardy hole for cutting tools.

A forging operation in which the length of a bar is reduced and its cross-section increased by endwise hammering or pressing. It is used to form bolt heads and similar thick ends.

A toothed wheel that transmits rotary motion and force to another toothed member with a definite velocity ratio. Teeth prevent slip and allow exact timing of shafts.

A transmission in which an endless belt running on two pulleys carries power between shafts. It is simple and absorbs shock but can slip under overload.

The ratio of the distance moved by the effort to the distance moved by the load in a machine. For pulleys it depends on the number of rope parts supporting the load.

Crude iron obtained directly from a blast furnace, high in carbon and impurities. It is remelted in a cupola to make cast iron or refined further to make steel.

A heavy, accurately finished flat plate used as a reference plane for marking out and checking work. Components are placed on it while heights are set with a scribing block.

Safety gear worn by the worker, such as goggles, gloves, apron, safety shoes and helmet, to reduce injury risk. It is the last line of defence after guarding and safe procedures.

The rules and practices followed in a workshop to prevent accidents, including guarding machines, keeping aisles clear and switching off power before adjustments. Housekeeping is a core part of it.