LGCSE Design & Technology (0189) common mistakes
LGCSE Design & Technology (0189) · Understand the traps and how to avoid them.
Writing the design brief as a single vague sentence (e.g. 'design a lamp') and then jumping straight to a final idea without stating a target market, constraints, or measurable success criteria.
Candidates treat the brief as a title rather than a design problem, so they have nothing to evaluate ideas against later and lose marks on analysis and evaluation. It happens because they have seen finished portfolios where the brief looks short, not realising the surrounding specification carries the weight.
What to do instead
Write the brief as one sentence naming user, context and purpose, then produce a numbered specification of at least six points, each testable (dimensions, cost ceiling, materials allowed, safety standard, power source). Label each point as a want or a need and revisit the list at every evaluation point so the iterative cycle is visible.
Describing a material only as 'strong' or 'light' without naming the property, the test, or the units, and without comparing it to an alternative.
Everyday language uses 'strong' for stiffness, hardness, toughness and tensile strength interchangeably. Candidates repeat the word from the brief without ever learning the distinction, and examiners cannot award property marks for an ambiguous adjective.
What to do instead
Build a comparison table for each project: material, density in kg/m3, tensile strength in MPa, stiffness (Young's modulus) in GPa, cost per kg, recyclability. Practise writing sentences such as 'aluminium 6061 has roughly one-third the density of mild steel at similar tensile strength, so it suits a handheld frame where mass matters more than cost'.
Drawing a third-angle orthographic projection with the plan above the front view, or the side view on the wrong side, and omitting hidden detail or centre lines.
Candidates copy the layout of a first-angle drawing seen in a textbook without learning which convention the exam uses, and they treat projection as 'three boxes' rather than a rule about where the observer stands relative to the object.
What to do instead
Memorise the third-angle rule as 'the view is placed on the side the observer looks from': front view centre, plan directly above, right side view to the right. Before drawing, sketch the glass box and unfold it. Then check line conventions deliberately: continuous thick for visible edges, dashed for hidden, chain for centrelines, thin for dimension and projection lines.
Calculating a gear train or pulley system by multiplying every ratio in sight, or ignoring the direction of rotation and the effect of an idler.
Candidates learn 'multiply the ratios' as a rule without tracking which gear is driver and which is driven, and they forget that an idler changes direction but not speed. Sign and direction errors then propagate through the whole answer.
What to do instead
Always label driver and driven on the sketch first, write the velocity ratio as driven teeth divided by driver teeth for each mesh, then multiply only the meshes in the power path. State direction explicitly ('output rotates opposite to input, reversed by the idler') and sanity-check: a small driver turning a large driven gear must slow the output and increase torque.
Treating a potential divider or transistor switching circuit as a black box: quoting 'the transistor amplifies' without calculating base current, or drawing an LED with no series resistor.
Candidates memorise circuit symbols and block diagrams but skip the arithmetic, often because they are unsure which values to substitute. Marks are then lost on the calculation and on the safety of the circuit.
What to do instead
For every circuit answer, show the governing equation, substitute values with units, and state the result. For an LED, calculate the series resistor from supply voltage minus LED forward voltage, divided by the chosen current. For a divider, compute output voltage as input times the lower resistor over the sum, and check that the transistor's base-emitter junction receives about 0.7 V before it conducts.
Describing a manufacturing process in one step ('injection mould the case') with no mention of tooling, draft angle, cycle, or why the process suits the batch size.
Candidates pick the process they have heard of rather than the one that fits quantity and geometry, and they have not seen the process, so they cannot describe its stages. Examiners want the sequence and the constraints, not the name.
What to do instead
For each candidate process, write a four-line card: tooling cost, typical batch size, one geometry constraint, one material constraint. Then answer in the pattern 'process, because batch size is X and tooling cost is justified, and the design must include Y (draft angle, uniform wall, gate position)'. Compare at least two processes before choosing.
Listing 'recyclable' or 'eco-friendly' as the whole sustainability argument, with no consideration of embodied energy, material separation, product life, or end-of-life route.
Sustainability is treated as a label to attach rather than a set of measurable trade-offs. Candidates do not know the difference between recyclability and recycled content, or between design for disassembly and design for landfill.
What to do instead
Structure every sustainability answer around four headings: material choice (recycled content, toxicity, scarcity), manufacture (energy, waste, water), use phase (efficiency, durability, repairability), end of life (disassembly, marking, take-back). Give at least one quantified comparison and one specific design change, such as using snap fits instead of adhesive so the casing can be separated.
Producing a risk assessment that lists hazards only ('saw is dangerous') without stating who is at risk, the likelihood and severity, or a control that changes the risk rather than just warning about it.
Candidates conflate hazard identification with risk assessment and default to 'wear goggles' for every row. They have not practised the hierarchy of control, so the controls they suggest are all personal protective equipment.
What to do instead
Use a five-column table: hazard, who is exposed, likelihood times severity, existing control, further action. Apply the hierarchy in order: eliminate, substitute, engineering control (guard, extraction, push stick), administrative (training, supervision, signage), then PPE last. For each row, name the specific machine or chemical and the specific control, and say what residual risk remains.
Presenting CAD work as screenshots of a finished render with no evidence of the modelling process, and treating CAM as automatic without checking toolpath, datum, or material behaviour.
Candidates believe a polished image demonstrates competence, so they hide the sketch constraints, the parametric history and the failed iterations. They also assume CAM output is always correct and never consider cutter diameter, feed rate, or workholding.
What to do instead
Show the modelling trail: initial sketch with constraints and dimensions, one feature tree view, one exploded or sectioned view, and one annotated render. For CAM, state the stock size, datum origin, tool diameter and type, stepover, feed and speed, and identify one likely failure (cutter deflection on a thin wall, poor clamping) with the mitigation.
Evaluating a final design only against the candidate's own opinion ('I think it looks good') rather than against the original specification, user feedback, and test data.
Candidates see evaluation as a concluding paragraph rather than a return to the brief, so the iterative cycle is never closed. They also avoid criticism because they think a negative comment loses marks, when the opposite is true.
What to do instead
Tabulate each specification point against evidence: measured dimension, user trial result, cost calculation, or test outcome, and mark met, partly met, or not met. Then state one specific modification with the reason and the predicted effect, and describe how it would be tested. This demonstrates the iterative cycle rather than merely claiming it.