Presentation techniques: rendering, exploded views, assembly drawings

Presentation Techniques – Graphics (IGCSE Design & Technology 0445)

1. Why Graphics Matter – Link to the Design Cycle

• Design brief → Specification → Idea generation → Development → Evaluation
• Graphics provide the visual language that records each stage of the cycle:
  • Sketches & concept drawings (idea generation)
  • Technical drawings – orthographic, isometric, exploded & assembly (development)
  • Annotated drawings for evaluation (e.g., tolerances, material choices)
• All marks for Component 2 (the design project) are awarded for how well the graphics support the brief, meet the specification and demonstrate realistic realisation.

2. Syllabus Checklist – Common Content (must be addressed in the project)

Requirement	How it appears in the graphics
Design brief & specification	Title block, material notes, performance criteria
Research & analysis	Annotated diagrams, comparison tables, sustainability icons
Idea generation (sketches, mind maps)	Free‑hand sketches, concept boards – not examined in detail but should be shown in the portfolio
Health & safety, sustainability, ergonomics	Notes on material selection, recycling symbols, safety warnings on assembly drawings
Use of CAD/CAM	Indicate if a drawing was produced digitally (e.g., “CAD – AutoCAD, SolidWorks”) and include a brief note on manufacturing method
Evaluation & improvement	Annotated revisions, tolerance analysis, finish specifications

3. Note to Teachers – Specialist Options

If your class also studies a specialist option (e.g., Resistant Materials or Systems & Control), supplement these notes with:

• Material property tables for metals, polymers, composites (Resistant Materials).
• Basic circuit symbols, control logic diagrams, and simple BOM entries for electronic components (Systems & Control).
• Relevant CAD modules (e.g., 3‑D modelling of gear trains, PCB layout).

4. Drawing Standards & Conventions

4.1 British Standards (BS 8888 & BS 308)

• Line‑type conventions – see Table 1.
• Dimensioning – arrows, extension lines, units (mm), tolerances (±0.2 mm unless otherwise stated).
• Scales – 1:1, 1:2, 1:5, 1:10, 1:20, 1:50. State the scale on the title block.
• Lettering & font – uppercase, sans‑serif (Arial or similar); 2 mm height for notes, 3 mm for titles.
• Projection symbol – always include the correct first‑angle or third‑angle symbol in the title block.

Line type	Purpose	Weight / Pattern
Visible edge	Actual contour	Thick solid (0.5 mm)
Hidden edge	Edge not directly visible	Thin dashed (0.25 mm, 2 mm dash/2 mm gap)
Centre line	Symmetry or circular features	Thin alternating long/short dashes
Construction line	Guidelines, layout aids	Very thin long dashes (0.18 mm)
Phantom / Section line	Cutting plane or hidden feature	Thin dash‑dot pattern

4.2 Title Block (template)

Field	Typical Content
Title	Product name (e.g., “Portable Bluetooth Speaker”)
Drawing number	e.g., “A‑01” (assembly), “P‑03” (part)
Scale	1:5
Projection symbol	First‑angle (shaded quadrant lower left)
Material / Finish	Aluminium – brushed, ABS – matte
Designer / Date	Student name, DD/MM/YY
CAD/CAM	Hand‑drawn / AutoCAD

5. Orthographic Projection

5.1 First‑Angle vs. Third‑Angle (quick reference)

Aspect	First‑Angle (UK)	Third‑Angle (US/Canada)
Relative placement of views	Top view below front view; right view on left side.	Top view above front view; right view on right side.
Projection symbol	Shaded quadrant lower left.	Shaded quadrant upper right.

5.2 Worked Example – Full Sheet (Front, Top, Side)

• All dimensions are placed on the outer side of the view.
• Hidden lines are used for internal features (e.g., mounting holes).
• Scale 1:5 is stated in the title block.

6. Isometric, Planometric & Perspective Drawings

6.1 Isometric Drawing

• Axes at 30° to the horizontal; equal foreshortening on all three axes (scale 1:1).
• Circles become ellipses; use an isometric grid or draw ellipses with a compass set to the isometric scale.
• Ideal for showing overall shape, hidden features and material finishes.

6.2 Planometric (Dimetric) Drawing

• Two axes drawn at the same angle (usually 45°) and the third at a different angle, giving a more realistic depth.
• Common grids: 45° × 45° (planometric) or 30° × 60° (axonometric).

6.3 Perspective Drawing

• One‑point perspective – single vanishing point on the horizon line; used for objects facing the viewer.
• Two‑point perspective – two vanishing points; used for objects turned away from the viewer.
• Construction steps (one‑point) are shown in the “Construction Steps” box below.

7. Rendering – Adding Realism

7.1 Rendering Techniques (quick guide)

Technique	Effect	Typical material / finish
Smooth shading	Gradual tonal change, highlights	Polished metal, glossy plastic
Fine hatching	Parallel lines, subtle texture	Brushed aluminium, wood grain
Cross‑hatching	Denser tone, rough texture	Stone, concrete, rough steel
Stippling	Fine dots for soft gradients	Matte plastics, fabrics
Colour rendering	Realistic colour, highlights, shadows	All consumer products where colour is a key feature

7.2 Material‑to‑Rendering Matrix

Material / Finish	Recommended rendering technique
Polished stainless steel	Smooth shading + sharp highlights
Brushed aluminium	Fine parallel hatching (spacing 0.5 mm)
Injection‑moulded ABS (matte)	Stippling or light cross‑hatching
Wood (oak, natural grain)	Fine hatching following grain direction
Carbon‑fibre composite	Cross‑hatching with a 45° angle pattern

7.3 Rendering Process (step‑by‑step)

1. Identify the material and finish from the design brief.
2. Choose the technique from the matrix above.
3. Decide on a light source – examiners expect light from the top‑left unless otherwise stated.
4. Apply the technique consistently:
   • Maintain even line spacing for hatching.
   • Use a softer pencil (2B–4B) for darker areas.
5. Introduce highlights (white or very light pencil) where the light hits directly.
6. If colour is required, colour‑block first, then add shading on top.
7. Check that dimensions, labels and notes remain legible.

8. Exploded Views – Showing Assembly Order

8.1 When to Use an Exploded View

• Complex products with several sub‑assemblies.
• When the examiner asks for “order of assembly” or “disassembly steps”.
• To highlight moving parts (gears, hinges, springs).

8.2 Procedure (with integration to BOM)

1. Draw a clear orthographic view of the fully assembled product (usually the front view).
2. Identify each sub‑assembly and individual part.
3. Move each part away from the centre along a line that follows the actual direction of assembly. Keep movement parallel to the drawing plane.
4. Maintain equal spacing where possible to avoid overlapping lines.
5. Label every part with the reference number that appears in the Bill of Materials.
6. Optional: add thin construction lines (dashed) to show the path of movement.

9. Assembly Drawings – The Complete Package

9.1 Key Features Required by the Syllabus

• Overall dimensions of the finished product.
• Reference numbers that match each part drawing and the BOM.
• Joining methods (screws, adhesives, snap‑fits, welding, etc.).
• Fastener specifications (type, size, material).
• Bill of Materials (BOM) table.
• Tolerances (e.g., ±0.2 mm) and surface‑finish notes (e.g., “Ra ≤ 0.8 µm”).
• Title block with scale, projection symbol, CAD/CAM note, and sustainability icon if relevant.

9.2 Sample Bill of Materials (BOM)

Ref.	Part description	Material	Qty	Fastener / Joining
1	Base plate	Aluminium 6061‑T6	1	–
2	Gear (large)	Steel 45 C	2	Set screw M3
3	Cover	Polycarbonate (transparent)	1	Snap‑fit
4	Mounting screw	Stainless steel 304	4	M4 × 12 mm

9.3 Layout of a Typical Assembly Drawing (full‑sheet example)

1. Centre of the sheet: Assembled orthographic view (front) with dimensions.
2. Surrounding the centre: Detailed part drawings (each with its own reference number).
3. Bottom centre: Bill of Materials.
4. Top‑right corner: Exploded view (optional but often awarded marks).
5. Title block: Bottom‑left – includes scale, projection symbol, CAD/CAM note, sustainability symbol.

9.4 Worked Example – Full Assembly Sheet (description)

A full‑sheet example (see placeholder image) includes:

• Title block with first‑angle symbol, scale 1:5, “Hand‑drawn” CAD note.
• Front orthographic view – all dimensions on the outer side, hidden lines for internal ribs.
• Three part drawings (Base plate, Gear, Cover) each with a 1:2 scale, reference numbers 1‑3.
• Exploded view showing the sequence 1 → 2 → 3 with dashed motion lines.
• BOM table matching the reference numbers.
• Notes: “All aluminium surfaces brushed – fine hatching”, “Tolerance ±0.2 mm on mating holes”, “Recyclable materials – 80 % aluminium, 20 % polycarbonate”.

10. CAD/CAM & Digital Presentation

• Digital drawings are acceptable if clearly labelled “CAD – SolidWorks” (or similar) in the title block.
• When using CAD, ensure line‑weight settings match the BS 8888 conventions (visible = 0.5 mm, hidden = 0.25 mm, construction = 0.18 mm).
• Exported PDFs must retain scale and dimension integrity – the examiner should be able to measure directly on the printed sheet.
• Include a brief note on the manufacturing process (e.g., CNC milling, injection moulding) if the question asks for “realisation”.

11. Sustainability & Environmental Impact in Graphics

• Indicate material recyclability in the BOM (e.g., “Aluminium – 100 % recyclable”).
• Show energy‑efficient finishes (e.g., “Low‑VOC paint”) as a note beside the relevant part.
• If the design uses renewable materials (bamboo, bioplastics), render them with appropriate texture (fine hatching for wood grain, stippling for bioplastic).
• Include a small sustainability icon (leaf) in the title block when the brief emphasises environmental considerations.

12. Comparison of Presentation Techniques

Technique	Shows	Primary Purpose	Typical Marks (Paper 5)
Rendering	Material, colour, texture, light & shadow	Visualise the final appearance	2–4
Exploded view	Component relationships, assembly order, sub‑assemblies	Explain how parts fit together	3–5
Assembly drawing	Overall dimensions, fasteners, BOM, tolerances	Provide a complete construction package	4–6
Orthographic projection	Accurate 2‑D views (front, top, side)	Show exact shape & dimensions	2–4
Isometric / Planometric / Perspective	3‑D visualisation (shape, depth, realism)	Give a quick overall impression	1–3

13. Assessment Tips – Maximising Marks

• Read the question carefully – note required views, scale, CAD/CAM requirement and any sustainability or material notes.
• Plan the sheet first – sketch a light layout, keep a 10 mm margin, decide where the title block, BOM and exploded view will sit.
• Use correct line weights – visible 0.5 mm, hidden 0.25 mm, construction 0.18 mm.
• Label everything – reference numbers, dimensions, material notes, fastener types must match the BOM.
• Select the right rendering technique – refer to the material‑to‑rendering matrix.
• Show tolerances and surface‑finish notes where the brief asks for “implementation and realisation”.
• Include a CAD/CAM note if the drawing was produced digitally.
• Address sustainability – use icons or notes to indicate recyclable or low‑impact materials.
• Proofread – check spelling of material names, fastener sizes, and that no dimensions are missing.
• Keep the drawing tidy – erase stray construction lines, keep spacing even, avoid crossing labels.

14. Summary

Effective graphics are the bridge between a design idea and a real product. By mastering drawing standards (BS 8888, BS 308), orthographic projection, isometric/planometric/perspective views, rendering, exploded views and assembly drawings, you demonstrate:

• Technical accuracy – dimensions, tolerances, line conventions.
• Visual communication – material, colour, texture, and assembly sequence.
• Integration with the whole design cycle – the drawings support the brief, specification, sustainability goals and the final evaluation.

Use the worked examples, matrices and checklists in this note to plan, execute and review every graphic product you create for the IGCSE Design & Technology exam.