Engineering Drawing: Sections and Conventions — CSEC Technical Drawing
Sectional views reveal the internal features of an object that would otherwise be hidden. Conventions are agreed standard ways of showing features.
Sectional views
A section is an imaginary cut through an object to show its internal detail.
- The position of the cut is shown by a cutting plane line (a chain line, thick at its ends, with arrows showing the direction of viewing).
- The cut surfaces are shown by hatching (section lines), drawn evenly spaced, usually at 45°.
- Hidden detail lines are normally omitted in a section, because the internal features are now visible.
Types of section
- Full section — the cutting plane passes right through.
- Half section — shows the outside on one half and the inside on the other.
Hatching rules
- Within a single component, the hatching is even in spacing and the same direction.
- Adjacent parts are hatched in opposite directions (or different spacing) to show they are separate.
- By convention, shafts, bolts, nuts, rivets and webs/ribs are NOT hatched when the cutting plane passes lengthwise through them.
Conventions
Conventions are standard symbols and simplified ways of showing common features (threads, springs, knurling, repeated holes) so drawings are understood by everyone, save time and reduce clutter.
Exam tips
- A section reveals internal features; cut surfaces are hatched at 45°.
- The cutting plane line shows where the section is taken.
- Hatch a single part evenly in one direction; adjacent parts in opposite directions.
- Remember bolts/shafts/ribs are not hatched in longitudinal section.