How are orthographic component and assembly production drawings produced from a 3D model?
Producing orthographic working drawings: first and third angle projection, the views needed, component and assembly detail drawings to British Standards.
An SQA Advanced Higher Graphic Communication answer on production drawings, covering orthographic projection in first and third angle, selecting the views needed, and producing component and assembly working drawings to British Standards.
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What this key area is asking
The SQA wants you to produce orthographic working drawings from a 3D model: understand first and third angle projection, select the views that fully define a part, and lay out component and assembly detail drawings to British Standards. These are the drawings a part is actually made from, so clarity and convention matter as much as the geometry.
Orthographic projection: first and third angle
The two systems show the same views but arrange them oppositely, so the projection symbol (a truncated cone) is always drawn to declare which is used. Misreading the system swaps left for right and top for bottom, so the SQA tests it directly. Australia, the UK and Europe commonly use third angle in education, but you must be able to read and produce both and to identify them from view placement.
Selecting the views
View selection is a judgement the marker rewards. A flat symmetric part may need only two views; a complex bracket may need three plus a section. The aim is completeness without repetition: every feature must be defined somewhere, but drawing a redundant view that adds nothing is poor practice. The front view choice matters because a good choice minimises hidden detail and makes the drawing readable.
Component and assembly drawings
These serve different readers. The component drawing goes to whoever makes the part and must carry every size and finish. The assembly drawing goes to whoever fits the parts and must make the relationships and the part schedule clear. Advanced Higher questions often present one and ask you to read specific information from it, so knowing what each type carries is essential.
Examples in context
A machined bracket detail drawing carries three views, a section, full dimensions and a surface-finish note. A gearbox assembly drawing shows the housing, shafts and gears in position with a ballooned parts list and only the key fitting dimensions. A flat gasket may need a single view plus thickness note. In each case the projection symbol, view choice and line conventions decide whether the drawing can be read and made without query.
Try this
Q1. State what symbol must be included on an orthographic drawing to show which projection system is used. [1 mark]
- Cue. The projection symbol (the truncated-cone symbol for first or third angle).
Q2. State why a single orthographic view cannot fully describe most 3D parts. [1 mark]
- Cue. One view shows only two of the three dimensions, so depth and hidden features are missing.
Q3. State the main purpose of an assembly drawing as opposed to a component drawing. [1 mark]
- Cue. To show how the parts fit together in their working positions (often with a parts list), rather than to manufacture a single part.
Exam-style practice questions
Practice questions written in the style of SQA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
SQA AH style4 marksAn orthographic drawing of a bracket shows a front view, a view to its right and a view above. State whether this is first or third angle projection, and explain how the position of the views tells you.Show worked answer →
The arrangement described, with the right-hand view placed on the right of the front view and the top view placed above the front view, is third angle projection.
In third angle, each view is placed on the same side as the direction from which it is seen, so the view looking from the right is drawn on the right and the view from above is drawn above. In first angle, the views are placed on the opposite side (the right-hand view would be drawn to the left).
Markers reward identifying it as third angle and explaining the placement rule (view drawn on the side it is viewed from), rather than just stating the answer.
SQA AH style3 marksExplain why a component drawing usually shows more than one view, and state what determines the minimum number of views needed.Show worked answer →
A single orthographic view shows only two of the three dimensions, so one view cannot fully describe a 3D part; additional views are needed to convey depth and features hidden in the first view.
The minimum number of views is determined by the complexity of the part: enough views must be drawn to define every feature unambiguously, so a simple symmetric part may need only two, while a complex part needs three or more plus sections.
Markers reward the point that one view cannot show all three dimensions, and that the number of views is set by what is needed to define the part fully without redundancy.
Related dot points
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