Tawjihi Vocational Engineering key terms

A drawing method that shows a three-dimensional object as separate flat views, usually front, top and side, with each view placed at right angles to the others.

A projection layout in which the object sits between the viewer and the drawing plane, so the view seen from the left is placed on the right of the front view.

A projection layout in which the drawing plane lies between the viewer and the object, so each view is placed on the same side as the direction from which it is seen.

A drawing that imagines part of the object cut away and hatched to reveal hidden internal features such as holes, bores and cavities, with cutting-plane lines marking where the cut is taken.

A thin line ending in arrowheads that carries a number stating the size or location of a feature, drawn parallel to the measured direction and kept clear of the object outline.

The total amount by which a stated dimension may vary while the part still functions, written as upper and lower limits or as a single plus-or-minus value.

The relationship between the sizes of a shaft and its mating hole, describing whether the assembly is free to move, turns with slight resistance, or is pressed together tightly.

Any metal whose main constituent is iron, such as mild steel, cast iron and high-carbon steel; these are magnetic and rust unless protected by paint, oil or coating.

A metal made by melting two or more elements together so the result has better properties than any single one, for example brass from copper and zinc.

A heat treatment that heats metal then cools it very slowly, softening it, removing internal stress and making it easier to cut, bend or machine.

A heat treatment that heats steel above its critical temperature and quenches it quickly in water or oil, producing a hard but brittle structure that is usually tempered afterwards.

Controlled heating and cooling of a metal to change its internal structure and therefore its hardness, strength, ductility or machinability, without altering the part's overall shape.

A sketch of one isolated body showing every external force acting on it, such as weight, normal reaction, friction and applied loads, with arrows giving direction and magnitude.

The state of a body at rest or moving at constant velocity, in which the sum of all forces and the sum of all moments acting on it are each zero.

The turning effect of a force about a point, calculated as the force multiplied by the perpendicular distance from that point to the line of action of the force.

The single force that would have the same effect as all the individual forces acting together on a body; it is found by vector addition, not by simple arithmetic addition.

The relationship stating that the current through a conductor is directly proportional to the voltage across it and inversely proportional to its resistance, written V equals I times R.

The opposition a component offers to current flow, measured in ohms; it depends on the material, length, cross-sectional area and temperature of the conductor.

A connection in which components form a single path, so the same current flows through each one and the supply voltage is shared among them in proportion to their resistances.

A connection in which components are joined across the same two points, so each receives the full supply voltage while the total current splits between the branches.

The rate at which the surface of a workpiece passes the cutting tool, usually expressed in metres per minute, chosen from the work material and tool material.

The distance the cutting tool advances relative to the workpiece per revolution or per stroke, controlling chip thickness and the surface finish produced.

A machining operation performed on a lathe in which the workpiece rotates against a stationary single-point tool to reduce diameter, face ends or cut threads.

The gradual loss of cutting-edge material through abrasion, heat and adhesion during machining, detected by flank wear, poor finish, noise or rising cutting force.

A measuring instrument with a main scale and a sliding jaw scale that allows readings to a fraction of a millimetre, used for outside, inside and depth measurements.

A precision measuring instrument using a calibrated screw and thimble to measure small thicknesses and diameters, typically reading to 0.01 millimetre with a friction or ratchet stop.

The smallest change in a measured quantity that an instrument can display or that an observer can reliably distinguish on its scale.

The process of comparing an instrument's readings against a known reference standard and recording any error, so that measurements can be trusted and corrected.

A gauge with go and no-go ends that checks whether a part's dimension lies within its permitted limits, without giving an actual measured value.

The order in which workplace hazards should be addressed: eliminate the hazard, substitute something safer, use engineering controls, then administrative controls, with personal protective equipment last.

Clothing and equipment worn by a worker, such as goggles, gloves, hearing protection and safety boots, to reduce exposure to hazards that cannot be removed by other means.

A structured review that identifies each hazard, estimates how likely and how severe the harm could be, and records the controls needed to reduce the risk to an acceptable level.

A safety procedure in which energy sources are isolated, locked and tagged before maintenance, preventing unexpected start-up or release of stored energy while work is in progress.

Scheduled inspection, lubrication, adjustment and replacement of parts carried out before a failure occurs, aimed at reducing breakdowns and extending equipment life.

Measuring equipment characteristics such as vibration, temperature, noise or oil contamination during normal running to detect developing faults before they cause a breakdown.

An itemised document listing materials, labour and work items with quantities, used to price a project and to compare tenders on the same basis.

The longest sequence of dependent activities through a project network, which sets the shortest possible project duration; any delay on it delays the whole project.

The output level at which total revenue equals total cost, so the business makes neither profit nor loss; above it each additional unit contributes to profit.