Maharashtra HSC Mechanical Technology (Vocational) key terms

A machine tool that rotates the workpiece against a single-point cutting tool to produce cylindrical surfaces, tapers, threads and faced ends. The work is held in a chuck or between centres.

The speed at which the workpiece surface passes the cutting tool, measured in metres per minute. It depends on workpiece and tool material and, with diameter, sets spindle rpm.

Milling in which the cutter teeth rotate in the same direction as the feed at the cutting point, so each tooth starts on a thick chip. Gives better finish but needs a backlash-free table.

A rotating end-cutting tool with helical flutes that cuts cylindrical holes. Common point angles are 118 degrees for general steel and 135 degrees for hard or thin materials.

A method of showing a solid object by separate views projected onto planes set at right angles, each view giving two dimensions only.

A projection layout in which the object lies between the observer and the plane, so the view from the front is placed below the top view. Standard practice in India.

A pictorial drawing in which the three axes are drawn 120 degrees apart and lengths are marked true along the axes without foreshortening, giving a quick three-dimensional view.

An iron-carbon alloy containing roughly 2 to 4 per cent carbon, produced in a cupola. It is strong in compression, damps vibration well, but is brittle and difficult to weld.

A heat treatment in which steel is heated to a chosen temperature, held there, then cooled very slowly, usually in the furnace. It softens the metal, relieves internal stress and improves machinability.

Rapid cooling of hot steel in water, oil or air to harden it by forming martensite. Quenched parts are brittle and are normally tempered immediately afterwards.

The smallest measurement an instrument can read. For a vernier it is the difference between one main-scale division and one vernier-scale division.

A measuring tool with a fixed main scale and a sliding vernier scale. It measures outside, inside, depth and step dimensions and usually reads to 0.02 mm.

A precision measuring instrument in which a calibrated screw and thimble convert rotation into small linear movement. It measures diameters and thicknesses, commonly to 0.01 mm.

A gauge with go and no-go ends that checks whether a feature lies inside its permitted maximum and minimum limits. It tells accept or reject but not the actual size.

The difference between the maximum and minimum permitted sizes of a dimension. It sets how much variation a manufacturing process may leave on a part.

A work-holding device bolted to a bench. Two jaws are closed by a screw to grip small parts for filing, sawing, drilling and chiselling.

A hand saw with a thin, fine-toothed blade held under tension in a frame. It is used for cutting metal bar, pipe and sheet, with tooth pitch chosen to match section thickness.

Thread-cutting tools. A tap is screwed into a drilled hole to cut an internal thread, while a die is turned over a rod to cut an external thread.

A foundry process in which molten metal is poured into a cavity shaped in a sand mould. The mould is broken after solidification to recover the casting.

A replica of the part to be cast, made slightly larger than the finished casting to allow for metal shrinkage. It is used to form the mould cavity.

Shaping a heated metal billet between two shaped dies that enclose it fully. The process gives accurate form, favourable grain flow and needs little machining.

An arc welding process in which a flux-coated consumable electrode melts into the joint. The coating burns to give shielding gas and forms a slag layer over the weld.

A sheet-metal press operation that cuts a closed shape out of sheet. The punched-out piece is the required product, in contrast with piercing where it is scrap.

A law stating that pressure applied to a confined fluid is transmitted equally in all directions. It is the basis of hydraulic presses, jacks and braking systems.

A valve that opens and releases fluid when system pressure rises above a set value. It protects pumps, cylinders and pipes from overpressure damage.

Planned inspection, cleaning, adjustment and replacement done on a schedule before failure occurs. It reduces breakdowns and keeps machines accurate and available.

Repair carried out only after a machine has failed. It avoids planning cost and effort but causes unplanned downtime, rushed work and lost production.

Placing oil, grease or a solid film between moving surfaces to cut friction and wear, carry away heat and protect the surfaces from corrosion.

Items such as helmet, safety glasses, gloves, ear plugs and safety shoes worn by a worker to reduce injury. It is the last line of defence after guarding and other controls.

A written authorisation for high-risk work such as hot work, confined-space entry or work on live systems, recording the precautions taken and the responsible signatures.

Deciding the sequence of operations, machines and work centres through which a product will pass. It is the first stage of production planning.

Fixing when each operation will start and finish on particular machines and workers, so that orders are completed by their promised dates.

Indirect costs such as rent, power, supervision, insurance and depreciation that cannot be traced to one product. They are recovered by adding a rate to direct cost.

The output or sales level at which total cost equals total revenue, so the business makes neither profit nor loss. Output above it gives profit.

A person who spots a business opportunity, gathers money, material and people, accepts the risk and sets up an enterprise.

A written document setting out the product, market, operations, money needed and expected returns of a proposed venture, used for planning and for seeking finance.

The money tied up in day-to-day running, such as raw material, wages, power and stock, that must be paid before customers settle their bills.