Drawing conventions
In third angle projection the view from above goes above the front view and the view from the right goes on its right; first angle swaps them. Switch between the two and watch the views move, cut the front view as a section, and pick a line type to see where the drawing uses it.
Each view sits on the side of the front view it looks from.
- Projection
- Third angle
- View from above
- Above the front view
- View from the right
- Right of the front view
- Symbol
- End view left of the cone
- Standards
- Preferred by AS 1100
How it’s calculated
Third angle puts the view from above above the front view and the view from the right on its right; first angle swaps each pair. The images are the same; only their places change. The symbol is a cone, small end left, with its end view on the side the left-hand view goes. Lines come in two widths, wide twice narrow, and their dashes are multiples of the width d: a dash 12d, a long dash 24d, a gap 3d, a dot about d.
Line types
| Line | ISO 128 | AS 1100 | Used for |
|---|---|---|---|
| Continuous wide | 01.2 | A | Visible edges and outlines, thread crests, the limit of a full thread, section arrows |
| Continuous narrow | 01.1 | B | Dimension, extension, leader and projection lines, hatching, thread roots, short centre lines, imaginary intersections, bend lines |
| Continuous narrow, freehand | 01.1 | C | The edge of a partial or broken view, cut or section, drawn by hand |
| Continuous narrow, zigzag | 01.1 | D | The same, drawn by machine; one of the two per drawing |
| Dashed narrow | 02.1 | F | Hidden edges and outlines |
| Dashed wide | 02.2 | E | Areas where a surface treatment is allowedAS 1100 E: hidden outlines, on a drawing that uses the wide dashed weight |
| Long-dash dotted narrow | 04.1 | G | Centre lines, lines of symmetry, pitch circles of gears and holes |
| Cutting plane | 10.2 + 04.1 | H | Where a section is cut: wide at the ends and at each change of direction, narrow chain between; arrows show the way it is viewed |
| Long-dash dotted wide | 04.2 | J | Areas with a limited requirement, such as a surface treatment |
| Long-dash double-dotted narrow | 05.1 | K | Adjacent parts, extreme positions of moving parts, parts in front of a cutting plane, outlines before forming |
How do you tell first from third angle on a drawing?
Look for the projection symbol near the title block: a cone drawn side on, small end to the left, beside its end view, two circles. When the circles are on the left, the drawing is third angle; on the right, first angle. AS 1100 prefers third angle and lets a sheet say it in words instead, “3RD ANGLE PROJECTION”. Without a symbol, compare two views: in third angle each one shows the face nearest the view beside it.