Topic 3 of 5 · Form 3
Sections, dimensioning and assembly drawings
A section shows the inside of an object as if it were cut along a cutting plane.
Notes for this topic 1 file, in order
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Sectional views
A section shows the inside of an object as if it were cut along a cutting plane.
- The cutting plane is shown by a chain line with thick ends and arrows showing the viewing direction, labelled (e.g. A–A).
- Cut surfaces are hatched with thin lines at 45°, evenly spaced. Adjacent parts are hatched in opposite directions.
- Do not hatch shafts, bolts, nuts, ribs and webs cut lengthways.
Dimensioning
- Dimension lines are thin with arrowheads touching extension (projection) lines; leave a small gap between the object and the extension line.
- Write dimensions above the line, readable from the bottom or right of the sheet; units in millimetres.
- Use Ø for diameter and R for radius. Do not repeat dimensions or dimension hidden detail.
Assembly drawings
Show how parts fit together, with a parts list giving item numbers, names, materials and quantities. Standard parts include nuts, bolts, washers and screws.
Exam tip: Hatching lines must stop at outlines and never cross a thick line.
Check yourself
- At what angle is hatching usually drawn?
- Which parts are not hatched when cut lengthways?
- What do the symbols Ø and R mean?
Show answers
- 45°.
- Shafts, bolts, nuts, pins, ribs and webs.
- Diameter and radius.
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