By the end of this topic, you should be able to...
construct and interpret 2D drawings and 3D models, including isometric, orthographic projection, assembly and exploded drawings.
Guiding Question
Why is it necessary for designers to prototype ideas as part of a design process?
💡 Did You Know? In 1999, NASA's $327 million Mars Climate Orbiter burned up in the Martian atmosphere because one engineering team used metric units while another used imperial—a catastrophe that precise technical drawings would have prevented.
Why Technical Drawing Exists
Before a single component is manufactured, before a mould is cut, before a supplier quotes a price — someone must unambiguously communicate the exact geometry, dimensions, tolerances and assembly relationships of a designed object. Technical drawing is that communication system.
Unlike a sketch, which communicates intent, a technical drawing communicates specification. It is a legally and contractually binding document in professional practice — a manufacturer who produces a component to drawing is not liable for design failures; one who deviates from drawing is.
The industrial designer Dieter Rams — whose design philosophy underpins much of modern product design thinking — noted that good design requires clarity of communication at every stage. Technical drawing is the formalisation of that clarity between the designer's mind and the manufacturer's machine.
The Role of Standards
Technical drawings derive their power from universal standardisation. A drawing produced in Finland can be manufactured in Malaysia because both parties read from the same standard — most commonly ISO (International Organisation for Standardisation) drawing standards.
Without standards, every drawing would require its own key, conventions would vary between companies, and manufacturing errors would multiply.
KEY STANDARDS IN TECHNICAL DRAWING
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ISO 128 → General principles of presentation
ISO 129 → Dimensioning principles
ISO 2768 → General tolerances
ISO 5456 → Projection methods
Drawing Sheet Conventions and Layout
Every technical drawing, regardless of type, follows standard sheet conventions that carry critical information.
Drawing Sheet Sizes
ISO PAPER SIZES FOR TECHNICAL DRAWINGS
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A0 → 841 × 1189 mm (large assembly drawings)
A1 → 594 × 841 mm (complex components)
A2 → 420 × 594 mm (standard components)
A3 → 297 × 420 mm (common for student work)
A4 → 210 × 297 mm (simple details, title blocks)
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The Title Block
Every professional technical drawing contains a title block — typically located in the bottom-right corner.
Line Types and Their Meanings
Line type is a formal vocabulary in technical drawing. Each line type carries a specific meaning that must be consistently applied.
Dimensioning
Dimensions are not decorative — they are manufacturing instructions.
DIMENSIONING RULES (ISO 129)
RULE 1 | Each dimension stated ONCE only. Never duplicate dimensions |
RULE 2 | Dimensions placed OUTSIDE the view where possible |
RULE 3 | Dimension lines do NOT cross extension lines or other dimension lines where avoidable |
RULE 4 | Units stated in title block, NOT repeated on every dimension (e.g. "All dimensions in mm") |
RULE 5 | Overall dimensions always included (height, width, depth) |
RULE 6 | Dimensions read from BOTTOM or RIGHT of the drawing sheet |
Orthographic Projection
Orthographic projection is the primary technical drawing system used to communicate the exact geometry of a 3D object using a set of related 2D views.
The Fundamental Principle
Imagine placing an object inside a transparent glass box. Looking at the object from six possible directions (front, top, bottom, left, right, back) produces six possible views. These views are then unfolded onto a flat plane — producing the orthographic drawing.
In practice, three views are typically sufficient to fully describe most objects:
The Three Standard Views
FRONT VIEW | Also called the Elevation. Shows the most descriptive face of the object |
PLAN VIEW | Also called Top View Shows the object from directly above |
END/SIDE VIEW | Also called Side Elevation Shows the object from left or right side |
Reading Orthographic Drawings
Reading an orthographic drawing requires cross-referencing all views simultaneously. No single view tells the complete story.
Interpretation Protocol
Step 1 | Identify the projection system (1st or 3rd angle) |
Step 2 | Identify the front/plan/end views |
Step 3 | Read overall dimensions: Height (front view), Width (front view), Depth (plan or side view) |
Step 4 | Identify hidden detail lines — these represent features not visible in that particular view (holes, recesses, slots) |
Step 5 | Cross-reference hidden lines across views to locate the ACTUAL position of hidden features in 3D space |
Step 6 | Read centre lines to identify axes of cylindrical features (shafts, holes, bosses) |
Step 7 | Read dimensions and tolerances for manufacturing specifications. |
Isometric Drawing
Isometric drawing is a pictorial drawing system — it produces a 3D-looking image of an object using a standardised projection method. Unlike orthographic projection, which separates views, isometric drawing combines all three principal directions into a single unified view.
When to Use Isometric vs Orthographic
USE ISOMETRIC WHEN:
• Communicating design concepts to clients
or non-technical audiences
• Producing design development sketches
with geometric accuracy
• Showing 3D spatial relationships clearly
• Producing exploded views (combined with
isometric convention)
USE ORTHOGRAPHIC WHEN:
• Producing manufacturing drawings
• Specifying exact dimensions and tolerances
• Communicating with manufacturers and
engineers
• Documenting complex hidden detail
• Required for formal design documentation
USE BOTH TOGETHER WHEN:
• Full design documentation package required
• Orthographic provides specification; isometric provides visual context
Assembly Drawings
An assembly drawing shows how components fit together to form a complete product or sub-assembly. It communicates spatial and functional relationships between parts — not the manufacturing detail of individual components.
Purpose and Function
COMMUNICATES TO:
Assembly workers on a production line
Quality control inspectors
Service and maintenance technicians
Product designers reviewing fit and function
ANSWERS THESE QUESTIONS:
How many parts are in this product?
In what sequence are parts assembled?
What is the spatial relationship between components?
Which fasteners or joining methods are used?
Which dimensions are critical to function (not manufacturing)?
Components of an Assembly Drawing
1. VIEWS OF THE ASSEMBLY
Typically orthographic views
Section views often included to show internal assembly relationships
Components shown in their ASSEMBLED position
2. PART NUMBERS (BALLOONS)
Circles with leader lines pointing to each component
Numbers refer to the parts list
3. PARTS LIST (BILL OF MATERIALS)
Table listing all components: Part Number | Part Name | Quantity | Material | Standard/Supplier
Typically located in top-right corner or adjacent to title block
4. ASSEMBLY DIMENSIONS
Only dimensions critical to the assembled product
NOT individual component dimensions (those belong on detail drawings)
Includes: overall dimensions, critical clearances, interface dimensions
5. NOTES
Assembly instructions
Torque specifications for fasteners
Adhesive or sealant requirements
Testing requirements
Exploded Drawings
An exploded drawing is a pictorial representation that shows the components of a product separated along their assembly axes, revealing the spatial relationship and assembly sequence of all parts simultaneously.
Purpose and Design Value
PRIMARY PURPOSE:
Communicate assembly sequence visually without requiring technical drawing literacy
AUDIENCES:
End users (IKEA furniture assembly manuals)
Service technicians (repair manuals)
Retail customers (product packaging)
Design teams (design review communication)
DESIGN VALUE:
Immediately communicates how many parts exist and their spatial relationships
Accessible to non-engineers
Identifies fasteners and their positions
Reveals the design logic of the product
Constructing an Exploded Drawing
Video coming soon....
3D Models
In contemporary design practice, 3D models are produced primarily through CAD (Computer Aided Design) software.
Wireframe Models
Description | Represent only the edges and vertices of a 3D form — like a cage of lines in 3D space |
Communicates | Basic 3D geometry and proportions |
Limitation | No surface information, visually confusing for complex objects |
Use context | Early design development, structural analysis setup |
Surface Models
Description | Define the outer skin/shell of a 3D form with no thickness or internal volume |
Communicates | Complex organic curves and aesthetic surfaces |
Limitation | No mass properties, cannot directly simulate structural behaviour |
Use context | Consumer product aesthetics, automotive body design, packaging design |
Solid Models (Parametric)
Description | Full volumetric representation with mass, material properties and feature history |
Communicates | Complete geometric, mass and material specification |
Limitation | Requires significant CAD skill to produce and modify |
Use context | Engineering components, manufacturing documentation, tolerance analysis |
Assessment Application
QUESTION 1 — CONSTRUCT
"Construct an orthographic drawing of the component shown in first-angle projection."
MARKING APPROACH:
Correct number of views: 1 mark
Correct projection method applied: 1 mark
Projection symbol shown: 1 mark
Correct line types (visible, hidden, centre lines): 1-2 marks
Dimensions correctly applied: 1-2 marks
Overall accuracy of geometry: 1-2 marks
STUDENT STRATEGY:
Always draw the crating box first
Work from the most descriptive view
Add centre lines before dimensions
State projection type explicitly
QUESTION 2 — INTERPRET
Using the orthographic drawing provided, state the overall dimensions and identify TWO features of the component."
MARKING APPROACH:
Correct dimensions extracted: 1 mark each
Features correctly identified with drawing evidence: 1-2 marks each
STUDENT STRATEGY:
Read ALL views before answering
Cross-reference hidden lines between views
Use dimensional evidence to support feature identification
Sources
Boundy, A.W. Engineering Drawing. 8th ed., McGraw-Hill, 2012.
Giesecke, Frederick E., et al. Technical Drawing with Engineering Graphics. 15th ed., Pearson, 2016.
International Organisation for Standardisation. ISO 128: Technical Drawings — General Principles of Presentation. ISO, 2020.
International Organisation for Standardisation. ISO 129-1: Technical Drawings — Indication of Dimensions and Tolerances. ISO, 2018.
International Baccalaureate Organisation. Design Technology Guide. IBO, 2023.
Simmons, C.H., and D.E. Maguire. Manual of Engineering Drawing. 4th ed., Butterworth-Heinemann, 2012.
Linking Questions
When creating physical prototypes, which ergonomic considerations should be taken into account? (A1.1)
To what extent are user-centred research strategies useful to gather feedback on models and prototypes of proposed design solutions? (A2.1)
How do designers use their knowledge of prototyping techniques to ensure effective modelling and prototyping? (A2.2)
Which aspects of material properties can be explored through modelling? (A3.1)
How can information about a proposed structural system, such as a product housing, be gathered using CAD modelling and contribute to the development of a design solution? (A3.2, B3.2)
How effectively can mechanical systems be mocked up and tested using modelling and prototyping? (A3.3, B3.3)
How can effective electronic systems be modelled virtually? (A3.4, B3.4)
How does the development of prototypes inform the choice of manufacturing techniques and production systems for a product? (A4.1, B4.1)
How can modelling and prototyping be used to inform the development of a product following a user-centred design (UCD) strategy? (B1.1)
To what extent is modelling and prototyping essential for inclusive design? (B2.2)
To what extent can the same materials used for modelling and prototyping be used in the material selection of a commercial product? (B3.1)