Skip to content

AALL1001 Engineering drawings and its concepts

Core purpose

  • Engineering drawing is the standardized graphical language used to communicate shape, size, position, tolerance, and construction intent.
  • The exam usually asks standard sheet facts, projection distinctions, scale meaning, and sectional-view recognition.

Standard drawing sheets

ISO A-series paper sizes are based on halving the previous size while preserving aspect ratio \(1: \sqrt{2}\).

Sheet Size in mm Key fact
A0 841 x 1189 Area is 1 square meter
A1 594 x 841 Half of A0
A2 420 x 594 Half of A1
A3 297 x 420 Half of A2
A4 210 x 297 Common document size
  • These dimensions are standard high-yield recall facts.
  • A3 is twice A4 area.
  • A2 is four times A4 area.

Dimensions and scale

  • Dimensioning states actual size, not drawn size.
  • Extension lines show where the measured limits begin and end.
  • Dimension lines carry the numerical value.
  • Arrowheads terminate dimension lines.

Scale means ratio of drawing size to actual size.

Scale type Example Interpretation
Full scale 1:1 Drawn size equals actual size
Reducing scale 1:10 Drawing is one tenth actual size
Enlarging scale 5:1 Drawing is five times actual size
  • A scale changes only the represented size on paper, not the actual dimension values.

Line types and line diagrams

Line type Use
Continuous thick Visible outlines
Continuous thin Dimension, projection, hatching
Dashed thin Hidden detail
Chain thin Center line, axis
  • A line diagram emphasizes connections or arrangement rather than exact appearance.
  • In engineering communication, line diagrams are common for circuits, layouts, and simplified mechanism representation.

Projection concepts

View type Distinguishing cue
Orthographic projection Several principal views, true dimensions on selected planes
Isometric view Three axes equally inclined, pictorial but measurable only by isometric rules
Pictorial view Gives visual impression rather than strict multiview detail
Sectional drawing Interior features shown by cutting plane
  • Orthographic projection is used for accurate manufacturing or construction communication.
  • Isometric is a pictorial method showing three dimensions in one view.
  • Orthographic and isometric are not interchangeable answers.

Orthographic projection

  • Front, top, and side views are the standard multiview idea.
  • Hidden lines may show invisible edges.
  • True shape is seen when the surface is parallel to the projection plane.

Isometric and pictorial views

  • In isometric view, the three principal axes are 120 degrees apart in the pictorial representation.
  • Equal foreshortening applies along all three isometric axes.
  • Isometric is a type of axonometric pictorial projection.

Sectional drawing

  • A sectional view imagines the object cut by a plane.
  • Hatching indicates the cut material region.
  • Hidden detail may be omitted in section for clarity.
  • Full section, half section, and offset section are common broader-study terms.

Recognition cues for engineering economics

  • "True size on principal plane" points to orthographic projection.
  • "Single view showing three dimensions" points to isometric or another pictorial view.
  • "Interior details revealed by cut plane" points to sectional drawing.
  • "A0 area" points to 1 square meter.

Common traps in engineering economics

  • Do not confuse A4 with letter size.
  • A-series sizes are not random; each is half the previous sheet.
  • Isometric is not perspective.
  • A dimension on the drawing states actual value unless specifically noted otherwise.

One-step examples for engineering economics

  • A 1:50 scale means 1 unit on drawing represents 50 units in reality.
  • An object interior hole is most clearly shown in section rather than a hidden-line-heavy orthographic view.
  • A4 dimensions are 210 mm x 297 mm.

Engineering-economics revision box

Memorize A0 to A4 sizes, especially A0 and A4. Orthographic is for exact multiview communication. Isometric is pictorial. Sectional views expose interior detail. Scale changes drawing size, not the actual stated dimension.