Section Views and Hatching Rules in Technical Drawing

A part with a bore, a pocket or an internal step quickly fills up with dashed lines. Put three or four internal features together and the view becomes unreadable. The answer is the section view: cut the part open on paper and draw what the cut reveals.

The cut is imaginary. Nothing is removed from the real part — only from the drawing, and only in the view marked as a section.

How a section is shown

Figure 5.1 — Showing the cutting plane and the resulting section A–A

Three things identify a section on a drawing:

The cutting plane trace — a chain line with thick ends, drawn on the view where the cut is taken.
The direction arrows at each end, showing which way you are looking.
The letters (A, B, C…) at the arrows, and the section itself labelled “SECTION A–A”.

In the section view, the material that the plane passed through is hatched. Where there was a hole, there is no material — so that area stays blank. This single distinction is what makes a section so much easier to read than a mass of dashed lines.

Types of section

Figure 5.2 — Full section, half section, local (broken-out) section and offset section

Full section. The plane passes right through the part. The standard case.
Half section. Used on symmetrical parts: one half is shown in section, the other half as an outside view. You get the inside and the outside in one view. Hidden lines are omitted from the view half.
Local (broken-out) section. Only a small area is opened up, bounded by a freehand break line. Ideal when a single hole or keyway needs explaining.
Offset section. The cutting plane steps sideways to pass through features that are not in line. The step itself is never drawn in the section view.

Hatching rules

Figure 5.3 — Hatch angle, the adjacent part rule and elements that are never hatched

Hatch lines are continuous thin, at 45°, evenly spaced.
All cut areas of the same part are hatched in the same direction and at the same spacing — in every view.
Two adjacent parts are hatched in opposite directions.
If a third part touches both, change the spacing or use 30° / 60° instead.
If the outline itself runs at 45°, hatch at 30° or 60° so the hatch does not disappear into the edge.
Sections thinner than about 2 mm (sheet, gaskets) are filled solid rather than hatched; adjacent thin parts get a small gap between them.
Dimension figures are never crossed by hatch lines — interrupt the hatching around them.

What is never hatched. When the cutting plane runs lengthwise through them, these are drawn as if uncut: bolts, nuts, washers, shafts, studs, keys, pins, rivets, bearing balls and rollers, gear teeth, and ribs or webs. Cutting them tells you nothing about their shape and only clutters the drawing. Cut across the same parts and they are hatched normally.

Reading a section

Find the cutting plane trace on the main view and note the arrow direction.
Match the letters to the section view.
Hatched = solid material. Blank inside an outline = a hole or cavity.
Count the hatch directions: each direction is a different part.
An unhatched element sitting inside the section is a shaft or a standard fastener.

Worked Example: Full Section of a Flanged Bushing

Let us see every sectioning rule on one part: a flanged bushing. On the left is the outside view — the bore can only be hinted at with dashed lines. When cutting plane A-A is passed through the axis and the full section is drawn on the right, the bore becomes a real edge, and every material surface the knife touches is hatched with 45° lines. The inside of the bore is empty space and is never hatched — and remember: solid standard parts such as shafts, bolts, rivets and keys are not hatched even when the cutting plane passes through them.

Test yourself

Why take a section at all?
To replace unreadable dashed lines with real, visible lines.
What does a blank area inside a sectioned outline mean?
There is no material there — it is a hole or cavity.
Why is a shaft not hatched in a longitudinal section?
It is solid; cutting it adds no information and confuses the view.
Two touching parts are hatched in the same direction. What is wrong?
Their boundary disappears and they read as one part. Adjacent parts must be hatched in opposite directions.
When would you use a half section?
On a symmetrical part, to show inside and outside in a single view.
Is the step of an offset section drawn in the section view?
No. The section is drawn as if the plane were flat.
A gasket 1 mm thick appears in a section. How is it shown?
Filled solid, not hatched.

Next lesson. The shape is now fully described. Lesson 6 puts numbers on it — the rules of dimensioning, the three dimensioning systems, and why chain dimensioning lets tolerances accumulate.