Why designers draw
A design has to travel from the designer's head to the person who makes it. Words are slow and can be misread. A technical drawing uses fixed rules, so a drawing made in Pune can be made correctly in Berlin.
- Freehand sketches: quick pencil drawings to explore ideas. Use light construction lines, then darken the final lines. Add notes (annotation).
- Models: card, foam or 3D-printed mock-ups to test size and feel.
- Formal drawings: accurate views with dimensions for making.
- CAD (computer-aided design): software that builds a 3D model and produces the views automatically.
Technical drawing is used in mechanical engineering, architecture, electrical wiring diagrams, furniture and product design. Careful observation (looking closely at real objects) is the first skill.
Pictorial drawings: isometric, oblique and perspective
- Isometric: vertical edges stay vertical; width and depth edges go at 30° to the horizontal. All three sizes are drawn true length. Circles become ellipses. Draw on isometric grid paper.
- Oblique: the front face is drawn flat and true; depth lines go back at 45°, often at half length (cabinet oblique) so it does not look too deep.
- Perspective: lines meet at one or two vanishing points, like a road going into the distance. It looks most real but sizes shrink with distance.
- Exploded view: the parts are pulled apart along lines to show how they fit together.
Choose the view that shows the most useful faces. Rendering (shading, colour, texture) makes presentation drawings clearer.
Orthographic projection: front, top and side views
Orthographic projection shows the object as separate flat views, each seen straight on. Imagine the object inside a glass box and each face flattened onto the glass.
- Front view (elevation): the view that shows the most about the shape.
- Top view (plan): looking straight down.
- Side view (end elevation): looking from the left or right.
Views line up: the top view sits exactly above or below the front view, so widths match; the side view sits beside it, so heights match.
First-angle and third-angle
Two layouts are used around the world. In first-angle (common in India, Europe) the top view goes below the front view and the left side view goes on the right. In third-angle (common in the USA) the top view goes above and the left view on the left. A small symbol (a cone drawn two ways) on the drawing tells which one is used.
Drawing standards: lines, dimensions, scale and CAD
| Line | Use |
|---|---|
| Thick continuous | Visible outlines and edges |
| Thin dashed | Hidden edges |
| Thin chain (long–short dash) | Centre lines, lines of symmetry |
| Thin continuous with arrows | Dimension and projection lines |
Dimensions are written in millimetres (no unit after the number when the drawing says "all dimensions in mm"). Each size appears once, outside the view where possible. Ø means diameter, R means radius.
Scale compares drawing size to real size. 1:2 means the drawing is half size; 2:1 means twice real size; 1:1 is full size. A title block gives name, date, scale, projection symbol and units. International standards (ISO 128, ISO 129 and national versions) fix these rules. Electrical diagrams use standard symbols for switches, lamps and cells instead of pictures.
CAD lets you draw once, change a size and see every view update, share files and send them to a laser cutter or 3D printer (CAM).
Try it
Take a matchbox or eraser. Sketch its isometric view on dotted paper, then draw its front, top and side views and measure each size with a ruler in mm.
Key formulas and definitions
- Isometric: width and depth at 30°, heights vertical, true lengths
- Oblique: front true, depth at 45° (often half length)
- Scale = drawing size : real size (1:2 = half size)
- First angle: top view below front view; third angle: top view above
- Dimensions in mm; Ø = diameter, R = radius
- Lines: thick = visible, dashed = hidden, chain = centre
Worked examples
1. A table top is 1200 mm long. How long is it on a drawing at scale 1:10?
1200 ÷ 10 = 120 mm on paper.
2. A small screw 8 mm long is drawn at scale 5:1. How long is the drawing?
8 × 5 = 40 mm. Enlarging scales help show tiny parts clearly.
3. Which view shows the height and width of an object?
The front view. The top view shows width and depth; the side view shows height and depth.
4. An edge is behind the object and cannot be seen from the front. How is it drawn in the front view?
As a thin dashed (hidden) line.
5. In first-angle projection, where does the top view go?
Directly below the front view, lined up so the widths match.
6. In an oblique drawing a box is 40 mm deep. How long is the depth line in cabinet oblique?
Half the real depth: 20 mm, drawn at 45°.
Common mistakes
- Drawing isometric depth lines at 45°. Isometric uses 30°; 45° is for oblique.
- Not lining up views, so widths in the front and top views do not match.
- Showing hidden edges as solid lines instead of dashed lines.
- Repeating the same dimension on several views, or writing cm when the drawing is in mm.