What you'll learn
When an object has internal features that cannot be seen from outside, engineers draw a sectional view — a view showing the object as if it had been cut open. For CSEC Technical Drawing you need to understand why sections are used, how to draw them with the correct hatching, the cutting plane, and the standard conventions for sectioning. This guide covers the purpose of sections, the cutting plane and hatching, the rules and conventions, and the parts that are not sectioned. By the end you should be able to draw a sectional view correctly and apply the standard conventions.
Key terms and definitions
Sectional view — A view showing an object as if cut through, to reveal internal features.
Cutting plane — The imaginary plane along which the object is cut, shown by a chain line on the drawing.
Hatching — Thin parallel lines drawn on the cut surfaces to show where material has been cut.
Convention — An agreed standard way of representing something on a drawing.
Hidden detail — Internal features normally shown by dashed lines, which sections reveal directly.
Cutting plane line — A chain line with arrows showing where the section is taken and the direction of viewing.
Web / rib — A thin supporting part of a component that is not hatched even when cut.
Assembly — A drawing showing several parts fitted together.
Core concepts
Why sections are used
A normal view shows only the outside of an object, and internal features have to be shown with dashed hidden-detail lines, which can become confusing on a complex part. A sectional view solves this by showing the object as if it had been cut open, so the internal features are revealed clearly as solid outlines. This makes the internal shape much easier to understand, which is why sections are widely used in engineering drawings.
The cutting plane
The position where the object is imagined to be cut is shown by the cutting plane line — a chain line (long-short-long) that is thickened or marked at its ends, with arrows showing the direction in which the cut face is viewed. The letters (such as A–A) label the section, and the sectional view is titled to match (for example "Section A–A"). This tells the reader exactly where the cut has been made and from which direction it is seen.
Hatching the cut surfaces
On a sectional view, the surfaces that have been cut are shown with hatching — thin, evenly spaced parallel lines, usually drawn at 45°. Hatching shows clearly which parts are solid material that the cut passes through. The rules for hatching include:
- Hatching lines are thin and evenly spaced.
- They are usually drawn at 45° to the main outlines.
- Different parts in an assembly are hatched in different directions (or spacings) so the separate parts can be told apart.
- Only the cut surfaces are hatched, not features behind the cutting plane.
Parts that are not sectioned
By convention, some features are not hatched even when the cutting plane passes through them, because hatching them would be misleading or unnecessary. These include ribs and webs (thin strengthening parts), shafts, bolts, nuts, rivets and similar solid items when cut lengthways. These are left unhatched so that the drawing is clearer and the parts are easily recognised. Knowing these exceptions is a common exam point.
Conventions in sectioning
Sectioning follows standard conventions so drawings are read the same way everywhere:
- Hidden detail is usually omitted in a sectional view, because the internal features are now shown as solid lines.
- Hatching does not cross the solid outlines of the part.
- The cutting plane is shown on the view where the section is taken, and the sectional view is labelled to match it.
Following these conventions keeps the drawing clear and unambiguous.
Types of section
There are several types of section used for different situations. A full section cuts straight through the whole object. A half section shows one half in section and the other half as an outside view, useful for symmetrical objects because it shows both the inside and the outside on one view. Knowing that different sections suit different objects helps you choose and interpret them correctly.
Other common drawing conventions
Sectioning is one of several conventions used to make engineering drawings clearer and quicker to produce. Other common conventions include abbreviated representations of repeated features — for example, a long shaft or a series of identical holes may be shown with a break line so the drawing does not have to show the whole length. Standard features such as screw threads are drawn using an agreed convention rather than showing every turn of the thread, which would be slow and cluttered. Knowing that conventions exist to save time and improve clarity, and being able to recognise the common ones, helps you both read and produce drawings efficiently.
Choosing where to take a section
Deciding where to take a section is an important skill. The cutting plane should be positioned so that it passes through the internal features you most need to show — for example, through the centre of a hole or a hollow part, so that the internal shape is revealed clearly. A poorly chosen cutting plane might miss the important features and fail to show what is needed. On symmetrical objects, the section is often taken along the line of symmetry. Being able to explain why a particular section position was chosen shows that you understand the purpose of sectioning, not just the mechanics of hatching.
Worked examples
Example 1: Why use a section
Why might an engineer draw a sectional view instead of using hidden detail lines? A complex internal shape shown with many dashed hidden-detail lines can be confusing. A sectional view shows the object cut open, revealing the internal features as clear solid outlines, which is much easier to understand.
Example 2: Reading a cutting plane
What does the cutting plane line with arrows labelled A–A show? It shows where the object has been cut to produce the section, and the arrows show the direction from which the cut face is viewed. The matching sectional view is titled "Section A–A".
Example 3: Hatching in an assembly
In an assembly of two parts shown in section, how are the parts distinguished? Each part is hatched in a different direction (or with different spacing). This makes it clear where one part ends and the next begins, so the separate components can be told apart.
Example 4: An unsectioned feature
A cutting plane passes lengthways through a bolt. Should the bolt be hatched? No. By convention, items such as bolts, nuts, rivets, shafts, ribs and webs are not hatched when cut lengthways, because hatching them would be misleading and make the drawing less clear.
Common mistakes and how to avoid them
A common error is hatching parts that should be left unhatched. Remember that ribs, webs, shafts, bolts, nuts and rivets are not sectioned (hatched) when cut lengthways.
Students often draw hatching too thick or unevenly spaced. Hatching must be thin, evenly spaced, and usually at 45°, and should not cross the solid outlines of the part.
Another mistake is showing hidden detail lines in a sectional view. Because the internal features are now shown as solid outlines, hidden detail is usually omitted in a section.
When drawing an assembly, do not hatch all parts the same way — use different directions so the separate parts can be distinguished.
Finally, always show and label the cutting plane on the relevant view and title the section to match (for example "Section A–A"), so the reader knows exactly where the cut is.
Exam technique for "Engineering Drawing: Sections and Conventions"
Be ready to explain why sections are used (to show internal features clearly instead of confusing hidden detail) and to draw hatching correctly — thin, even, at 45°, only on cut surfaces.
Know the conventions, especially which parts are not hatched (ribs, webs, bolts, nuts, rivets, shafts) and that hatching in an assembly runs in different directions for different parts. Be able to identify and use the cutting plane line with its arrows and section label.
Apply the conventions carefully in any drawing, and omit hidden detail in the section. Use precise terms — sectional view, cutting plane, hatching, convention — throughout, as accurate application of the conventions is exactly what the examiner rewards.
Quick revision summary
- A sectional view shows an object as if cut open, revealing internal features as clear solid outlines instead of confusing hidden-detail lines.
- The cutting plane line (a chain line with arrows, labelled e.g. A–A) shows where the cut is and the viewing direction; the section is titled to match.
- Hatching (thin parallel lines, usually at 45°) marks the cut surfaces; different parts in an assembly are hatched in different directions.
- Some parts are not hatched when cut lengthways: ribs, webs, shafts, bolts, nuts and rivets.
- Hidden detail is usually omitted in a section.
- Full sections cut through the whole object; half sections show inside and outside on a symmetrical part.