Engineering Drawing
Core concepts
Engineering drawing tests spatial reasoning and standard convention. You must know the first-angle and third-angle projection systems and their symbol, orthographic views (front, top, side), isometric and oblique projection, sectioning and hatching conventions, dimensioning rules, line types and their precedence, and standard abbreviations. Familiarity with limits, fits and tolerances, surface roughness symbols, and the conventional representation of threads, springs and welded joints is also expected.
Traps that recur
The most frequent error is mixing projection systems: in first angle the view from above is placed below the front view, which is the reverse of third angle. Candidates also draw hidden edges as continuous lines instead of dashed, dimension to the wrong reference edge, or omit the centre line for symmetrical features. In isometric drawing, true lengths are drawn along the isometric axes but not along non-isometric lines; foreshortening is often forgotten. Section lines must not cross dimension text, and hatching direction should be uniform across a single part.
Worked example
A hexagonal prism of 30 mm base side and 50 mm height rests on its base with one base edge parallel to the vertical plane. In the top view, draw the hexagon with the chosen edge horizontal; project the front view as a rectangle 50 mm tall and 60 mm wide (the distance across corners for a hexagon of side 30 mm is 60 mm). Rule of thumb: across corners equals twice the side, across flats equals √3 times the side.
Practice habit
Sketch the three views of any object you see daily, and always label the projection symbol before starting.