BGCSE Design & Technology cheat sheet

The design cycle order is: identify the need, write a design brief, research, generate specifications, produce ideas, develop and model, test and evaluate, manufacture, then evaluate against the brief.

A design brief states the problem and constraints in one or two sentences; a specification lists measurable criteria (size, cost, mass, safety, finish) that a solution must satisfy.

A design specification criterion must be testable: 'must hold at least 5 kg' is valid; 'must look nice' is not, because it cannot be measured.

Analysis of a problem separates the client's stated need from the underlying need; the designer records both before generating solutions.

Divergent thinking generates many options without judgement; convergent thinking then selects against the specification using a weighted decision matrix.

In a weighted decision matrix, score each option 1-5 per criterion, multiply by the criterion weight, and sum; the highest total is the justified choice.

Anthropometric data (reach, grip, eye height, seat height) is taken from population percentile tables, usually the 5th percentile female to 95th percentile male range.

Ergonomic design matches the product to human body dimensions, force capability, and sensory limits; poor ergonomics shows as fatigue, strain, or error rate.

Evaluation compares the finished outcome with the original specification criterion by criterion, recording evidence and stating justified improvements.

Hardness is resistance to surface indentation and abrasion; toughness is resistance to shock and impact without fracture; these are independent properties.

Ductility allows a material to be drawn into wire; malleability allows it to be shaped by hammering or rolling into sheet without cracking.

Elastic deformation is reversible and returns to original shape; plastic deformation is permanent and occurs once the elastic limit (yield point) is passed.

Stiffness is measured by Young's modulus (stress divided by strain in the elastic region); a stiffer material deflects less under the same load.

Thermoplastics (acrylic, HDPE, polystyrene) soften repeatedly on heating and can be recycled; thermosets (epoxy, polyester resin, melamine) cure once and char rather than melt.

Ferrous metals contain iron and are magnetic; low-carbon steel is ductile and weldable, high-carbon steel is harder and more brittle, cast iron is hard but brittle in tension.

Non-ferrous metals contain no iron: aluminium is light and corrosion-resistant, copper conducts electricity and heat, brass (copper-zinc) machines well.

Seasoning reduces moisture content in timber to limit shrinkage, warping, and splitting; kiln seasoning is faster than air seasoning but costs more energy.

Composite materials combine reinforcement and matrix: GRP (glass fibre in polyester resin) gives high strength-to-weight ratio; plywood crosses grain direction for balanced strength.

Personal protective equipment rules: safety glasses for all cutting and drilling, dust mask when sanding or machining timber, ear defenders above roughly 85 dB, no loose sleeves or jewellery near rotating tools.

A tenon saw has a stiffened back and fine teeth for accurate straight cuts and joinery; a rip saw has coarse teeth for cutting along the grain; a crosscut saw cuts across the grain.

A coping saw has a thin, easily replaced blade held under tension for curved cuts in thin material; a fretsaw is used for very fine internal curves.

A try square checks and marks 90-degree angles; a sliding bevel transfers or marks any angle; a marking gauge scribes a line parallel to a face side or face edge.

Drill speeds follow the rule: harder material and larger bit diameter require lower rotational speed; use cutting lubricant on metals and clear swarf with a brush, never by hand.

A centre punch marks hole positions in metal so the drill does not wander; a pilot hole is smaller than the finished hole and guides the final drill.

A bench vice holds work below elbow height; a machine vice or clamps must secure work on a drill table, and the chuck key must be removed before starting.

Sharp tools require less force and are safer than blunt tools because they cut rather than slip; a blunt chisel causes more hand injuries than a sharp one.

Electrical safety: check plugs and leads for damage, keep cables away from cutters, use residual current device protection, and isolate power before changing blades or bits.

One-off, batch, and mass production differ in tooling cost per unit: one-off has minimal tooling, mass production has high tooling cost but the lowest unit cost at high volume.

Injection moulding forces heated thermoplastic into a closed steel mould; it suits high volume, gives good surface finish, and requires draft angles for ejection.

Vacuum forming heats a thermoplastic sheet, draws it over a former, and removes air beneath; it suits shallow shapes without undercuts and is used for packaging trays.

Blow moulding inflates a heated thermoplastic parison inside a mould to make hollow items such as bottles; extrusion produces continuous constant-cross-section profiles.

Die casting forces molten non-ferrous metal into a steel die for accurate, thin-walled parts; sand casting uses a disposable sand mould and suits larger, simpler iron and aluminium parts.

Soldering joins metals with a filler alloy that melts below the parent metal; a flux removes oxide during heating, and the joint must be clean and mechanically held while cooling.

Welding fuses the parent metal, often with a filler rod; it is stronger than soldering or brazing but distorts the work and needs edge preparation.

Jigs hold the work and guide the tool; fixtures hold the work only. Both increase repeatability and reduce marking-out time in batch production.

Quality control uses go/no-go gauges and sampling to check dimensions against tolerance; tolerances state the permitted upper and lower limits of a dimension.

Third-angle projection places the plan above the front elevation and the end view to the left; first-angle projection places the plan below and the end view to the right.

A hidden detail is drawn as a broken line of short dashes; a centre line is a long-dash-short-dash chain used to locate holes and axes of symmetry.

Dimension lines are thin continuous lines with arrowheads at both ends; extension lines run from the feature to the dimension line, and dimensions are read from the bottom or right of the sheet.

British Standards drawing line widths: thick continuous lines (about 0.7 mm) for outlines, thin continuous lines (about 0.35 mm) for dimension, hatching, and projection lines.

Orthographic views show true shape and size but not depth; isometric projection shows three faces with vertical edges true and axes at 30 degrees to the horizontal.

Oblique projection draws the front face true shape with receding edges at 45 degrees; one-point perspective uses a single vanishing point for realistic depth.

Scale is drawing length divided by real length: a scale of 1:5 means 1 unit on the drawing represents 5 units in reality.

Section views use evenly spaced hatching at 45 degrees to show cut material; adjacent parts are hatched in opposite directions, and shafts and bolts are not sectioned lengthwise.

A flowchart uses standard symbols: rectangle for process, diamond for decision, parallelogram for input or output, and arrows to show sequence.

A structure is stable when the line of action of its centre of gravity falls within its base of support; widening the base or lowering the centre of gravity increases stability.

Static equilibrium requires the sum of forces and the sum of moments about any point to be zero; moment equals force multiplied by perpendicular distance (M = F x d).

Tension pulls a member apart, compression pushes it together, shear slides layers past each other, torsion twists, and bending combines tension and compression across a beam.

Triangulation gives rigidity because a triangle cannot change shape without one side changing length; a square frame needs a diagonal brace.

A beam's strength depends on cross-section shape: an I-beam places material far from the neutral axis, raising stiffness for the same mass.

Mechanical advantage (MA) equals load divided by effort; velocity ratio (VR) equals effort distance divided by load distance; efficiency equals MA divided by VR, expressed as a percentage.

A lever is a bar pivoting at a fulcrum: first class has the fulcrum between load and effort, second class has the load between them, third class has the effort between them.

A gear ratio equals driven teeth divided by driver teeth; it multiplies torque and reduces speed when the ratio is greater than one.

A cam converts rotary motion into reciprocating motion; a follower rises on the cam's rise, dwells on the base circle, and returns on the fall.

Power equals energy transferred divided by time (P = E/t), and electrical power equals voltage multiplied by current (P = V x I), measured in watts.

Ohm's law states V = I x R; resistors in series add (R total = R1 + R2), and in parallel the reciprocal sum applies (1/R total = 1/R1 + 1/R2).

Energy cost equals power in kilowatts multiplied by time in hours multiplied by the price per kilowatt-hour.

A fixed resistor uses the colour code: black 0, brown 1, red 2, orange 3, yellow 4, green 5, blue 6, violet 7, grey 8, white 9; the third band is the multiplier.

A light-emitting diode conducts in one direction only and needs a series resistor to limit current; the longer leg is the anode and connects toward the positive supply.

A potential divider gives output voltage V out = V in x R2 / (R1 + R2); it is used to feed a sensor signal to a transistor or comparator.

A transistor can be used as a switch: a small base current controls a larger collector current, allowing a sensor circuit to drive a motor or lamp.

Renewable energy sources (solar, wind, hydro, biomass) are replenished naturally; non-renewable sources (coal, oil, gas, nuclear fuel) are finite.

Energy efficiency equals useful energy output divided by total energy input, expressed as a percentage; losses usually appear as heat, sound, or friction.

The six Rs hierarchy in order: refuse, reduce, reuse, repair, recycle, recover; disposal is the last resort.

Life cycle assessment stages are: raw material extraction, manufacture, distribution, use, and end of life; each stage is scored for energy, water, emissions, and waste.

A product's carbon footprint is the total greenhouse gas emitted across its life cycle, expressed as carbon dioxide equivalent.

Design for disassembly uses reversible fasteners, standard fixings, and material labels so components can be separated and recycled at end of life.

Planned obsolescence shortens product life through fashion, function, or technical limitation; it raises resource use and is a recognised ethical concern.

Inclusive design considers age, ability, size, and culture so a product works for the widest practical range of users without adaptation.

Intellectual property protection includes patents for new technical function, registered designs for appearance, trademarks for brand identity, and copyright for drawings and text.

Health and safety legislation places duties on designers and manufacturers to identify hazards, reduce risk, and provide adequate warnings and instructions.

Fair trade and ethical sourcing consider labour conditions, child labour, and fair pricing in the supply chain, not only product cost and function.

The project folio follows the design cycle: problem analysis, brief, specification, research, ideas, development, planning, making, testing, and evaluation.

Each specification point must be traceable to a design decision and to later testing evidence; unaddressed criteria are a common cause of lost marks.

A cutting list records each component's material, dimensions, and quantity; a production plan sequences operations and identifies tools, jigs, and quality checks.

Working drawings for manufacture include overall sizes, joint details, component dimensions, tolerances, and a parts list.

A risk assessment records hazard, persons at risk, existing control, risk rating before and after control, and the responsible person.

Photographic evidence should show stages of making, not only the finished product, because it verifies process skills and quality control.

Testing must use the specification criteria: record the method, the measured result, and a pass or fail judgement for each criterion.

Evaluation distinguishes objective evidence (measured test data) from subjective opinion (user comments) and proposes specific, justified modifications.

Time planning tools include a Gantt chart for overlapping tasks and a flow chart for process sequence; both identify dependencies and deadlines.