Orthogonal drawing and Australian Standards: HSC Industrial Technology Graphics Technologies

What this dot point is asking

Orthogonal drawing is the backbone of the Graphics Technologies focus area: it is how a three-dimensional object is described precisely and unambiguously in two dimensions. NESA expects you to produce and interpret multiview drawings using third-angle projection and the Australian Standards conventions for views, line types, dimensioning, sectioning and scale. These conventions let any reader anywhere build the object exactly as intended, so this content underpins both the written examination and the drawings in your Major Project folio.

What orthogonal drawing is

An orthogonal (or orthographic) drawing uses parallel lines of sight, looking straight at the object so each view shows true shape and size without perspective distortion. Because one view cannot fully describe a solid, several views are combined, up to six in all, though most objects need only three. Each view shows the object as if you were looking directly at one face, so dimensions can be read and measured accurately.

Third-angle projection

The views must be arranged in a standard order so a reader knows which is which. Australia uses third-angle projection, in which each view is placed on the side of the front view from which it is seen: the top view goes above the front, the right-side view goes to the right, and so on. A standard projection symbol on the drawing tells the reader which system is used. Arranging views correctly is essential, because a misplaced view makes the drawing impossible to interpret.

Line types and conventions

Australian Standards define a set of line types, each with a meaning:

• Continuous thick lines show visible outlines and edges.
• Dashed lines show hidden edges behind the surface.
• Thin chain lines show centrelines and axes of symmetry.
• Thin continuous lines show dimension and projection lines.

Using the correct line type for each feature is what lets a reader tell a visible edge from a hidden one or a centreline, so consistent line work is a basic mark of competence.

Dimensioning

Dimensions tell the reader the exact sizes. The standard rules keep them clear and unambiguous: dimension lines with arrowheads, extension lines projecting from the feature, figures placed to be read from the bottom or right, and each dimension given once only. Dimensions are taken from datum surfaces and follow the standard order so the part can be made to size. Over-dimensioning or missing dimensions both cause errors, so dimensioning is done carefully and completely.

Sectioning and scale

When internal features cannot be shown clearly with hidden lines, a sectional view cuts through the object and shades the cut surface with hatching, revealing the inside as if sliced open. Section planes and hatching follow standard conventions.

Drawings are produced to a stated scale because objects rarely fit the page at full size. A scale such as one to two means the drawing is half full size, and the scale is always stated so dimensions are never measured off the drawing but read from the figures. Following the standard for scale, title block and sheet layout completes a professional drawing.

Why standards matter

The whole point of Australian Standards conventions is communication. A drawing made to the standard can be read and built by anyone in industry, anywhere, without speaking to the designer. When you produce orthogonal drawings in your folio, follow the conventions exactly, because in this focus area the standard itself is part of what is assessed.