SQA Advanced Higher Graphic Communication Technical Graphics: a complete overview of 3D CAD modelling, assembly, production drawings, sections, dimensioning and British Standards
A deep-dive SQA Advanced Higher Graphic Communication guide to the Technical Graphics context. Covers 3D CAD modelling techniques and strategy, assembly modelling, orthographic production drawings, sectional views, dimensioning and tolerancing, British Standard conventions, and pictorial and rendered illustration.
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What Technical Graphics actually demands
Technical Graphics (TG) is the engineering and product-modelling side of Advanced Higher Graphic Communication. It runs from building solid 3D CAD models, through assembling them and documenting them as orthographic and sectioned production drawings, to dimensioning and finishing those drawings to British Standards, and finally to illustrating the form pictorially. The examiners reward efficient, well-planned models, the correct choice of views and sections, accurate reading and calculation of tolerances and fits, and strict conformance to drawing conventions. This guide walks through each key area, then sets out how the SQA examines them. Each key area has a matching dot-point page with worked questions; this overview ties them together.
3D CAD modelling techniques
Models are built from feature operations: extrude (constant section along a straight path), revolve (a profile about an axis, for bodies of rotation), sweep (a constant profile along a curved path), loft (a blend between differing profiles) and shell (hollowing to a constant wall thickness), refined with fillets, chamfers and patterns. The Advanced Higher skill is choosing the most efficient technique and justifying it.
Modelling strategy
A robust model is planned: a sensible base feature and datums, sketches fully constrained by geometric and dimensional constraints, and an ordered, named feature tree. Because the model is parametric, editing a driving dimension updates the geometry and any linked drawings automatically, which is what makes design iteration fast.
Assembly modelling
Components are combined with mating constraints, concentric, mate, distance and angle, that remove degrees of freedom while leaving the working motion free. Large products are split into sub-assemblies. The assembly yields an exploded view that shows assembly order and a parts list (BOM) that tabulates each item by number, description and quantity, keyed to balloons.
Production drawings
A 3D model is documented as orthographic working drawings in first or third angle, with the projection symbol declared. You draw the minimum views that define the part, choose a clear front view, and produce component (detail) drawings for manufacture and assembly drawings for fitting.
Sectional views
Sections reveal internal features: full, half, part (local), revolved and removed. The cutting plane is shown as a labelled chain line with arrows, cut material is hatched, adjacent parts hatched differently, and standard items (bolts, shafts, ribs) are not sectioned by convention.
Dimensioning and tolerancing
Drawings are dimensioned to British Standards from sensible datums, each feature once. Tolerances (bilateral or unilateral) state permitted variation; fits (clearance, interference, transition) set how a hole and shaft relate; and surface finish is specified where it matters. Reading limits and selecting the right fit for the function are core skills.
British Standard conventions
BS 8888 conventions make a drawing universally readable: fixed line types (visible, hidden, centre, cutting plane), projection and machining symbols, standard abbreviations (DIA, R, CRS, PCD, CSK, HEX), and conventional representations of features such as screw threads.
Pictorial and illustration drawings
Form is communicated pictorially by isometric and planometric (parallel, measurable), and perspective (converging, realistic), and by rendered CAD illustration that adds material, colour, light and shadow. The skill is matching the pictorial type to the audience and purpose.
How Technical Graphics is examined
A typical SQA profile for the TG side of the question paper:
- Modelling. Choosing and justifying modelling techniques and a modelling strategy from a given part, and reasoning about how a model would be edited.
- Drawings. Interpreting orthographic and sectioned drawings, identifying projection systems, line types and conventions, and reading sizes, tolerances and fits.
- Standards. Applying British Standard conventions and abbreviations, and recognising parts that are not sectioned.
- Illustration. Choosing and justifying pictorial types and the purposeful use of rendering.
Check your knowledge
A mix of recall and reasoning questions covering Technical Graphics. Attempt them, then check against the solutions.
- Name the modelling feature that creates a body of rotation. (1 mark)
- State what it means for a sketch to be fully constrained. (1 mark)
- Name the constraint that aligns the axes of a shaft and a bore in an assembly. (1 mark)
- State what the projection symbol on a drawing declares. (1 mark)
- State what hatching on a sectional view represents. (1 mark)
- State how the tolerance on a dimension is calculated from its limits. (1 mark)
- State what a thin chain line represents on a working drawing. (1 mark)