How are sectional views used to reveal internal features on a drawing?
Producing and interpreting sectional views: full, half, part, revolved and removed sections, cutting planes, hatching conventions and parts not sectioned.
An SQA Advanced Higher Graphic Communication answer on sectional views, covering full, half, part, revolved and removed sections, cutting planes, hatching conventions, and the parts that are conventionally not sectioned.
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What this key area is asking
The SQA wants you to produce and interpret sectional views that reveal internal features: choose between full, half, part (local), revolved and removed sections, show the cutting plane correctly, apply hatching to British Standards, and know which parts are conventionally not sectioned. Sections are how a drawing shows what is hidden inside a part.
Types of section
Choosing the type is a judgement. A full section suits a part with internal detail throughout; a half section suits a symmetrical part where one view can serve double duty; a part section suits a localised internal feature where a full cut would be wasteful. Revolved and removed sections efficiently show the changing profile of long features without extra full views.
The cutting plane and hatching
Hatching distinguishes solid material that the plane has cut from voids and from surfaces beyond the plane. On an assembly, adjacent parts are hatched differently, by opposing the angle or changing the spacing, so the boundary between parts is clear. The cutting-plane line, arrows and matching section label are all required, because they tell the reader exactly where and which way the part has been cut.
Parts conventionally not sectioned
This is a frequently tested convention. A web shown solid and hatched could imply a thick block of material rather than a thin stiffening rib, so it is left unsectioned. Standard fasteners have no internal detail worth revealing, so cutting them clutters the view. Knowing these exceptions, and applying them, is exactly the kind of standards knowledge the question paper rewards.
Examples in context
A valve body is shown in full section to reveal its internal passages. A symmetrical pulley is shown in half section, inside on one half and rim profile on the other. A bracket with a stiffening web is sectioned, but the web is left un-hatched. A shaft with a keyway is shown with the shaft unsectioned and the keyway by a local break-out. Each choice reveals exactly what the reader needs without misleading them.
Try this
Q1. State what hatching on a sectional view represents. [1 mark]
- Cue. Solid material that the cutting plane has cut through.
Q2. Name two standard items that are conventionally not sectioned (not hatched). [1 mark]
- Cue. Any two of: bolts, nuts, shafts, keys, rivets, pins, ribs or webs (cut longitudinally).
Q3. State one advantage of a half section over a full section for a symmetrical part. [1 mark]
- Cue. It shows internal and external detail together on one view.
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 marksA drawing of a bolted assembly shows a full section through the centre. State two items that should not be cut by the section even though the cutting plane passes through them, and explain why.Show worked answer →
Standard parts such as bolts, nuts, shafts, rivets, keys and webs (ribs) are conventionally not sectioned (not hatched) even when the cutting plane passes through them along their length.
They are left unsectioned because hatching them would clutter the drawing and could be misleading: there is no useful internal detail to show, and showing a solid web hatched can wrongly imply a thick solid mass.
Markers reward naming at least two such items (for example a bolt and a web) and the reason that sectioning them adds no useful information and can mislead, so convention leaves them un-hatched.
SQA AH style3 marksExplain the difference between a full section and a half section, and state when a half section is preferred.Show worked answer →
A full section cuts the part right through along the cutting plane, so the whole view is sectioned and all the internal detail along that plane is exposed.
A half section cuts only half of a (usually symmetrical) part, showing internal detail on one half and the external view on the other, divided by a centreline.
A half section is preferred for a symmetrical part because it shows both the inside and the outside on one view, saving a separate external view.
Markers reward the contrast between cutting fully and cutting half, and the point that a half section conveys internal and external information together on a symmetrical part.
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