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Orthographic Projections: First and Third Angle Guide.

EngineeringTry the interactive 3D model →

Orthographic projection is a method of drawing a 3D object as exact 2D views using parallel projectors that strike the drawing plane at right angles. The three standard views are the front view (elevation), top view (plan) and side view (end view) — together they describe an object's true shape and size with no perspective distortion.

It is the universal language of manufacturing: a machinist must cut metal from your drawing alone, and one misread view scraps the part. First-angle and third-angle are the two layout conventions — knowing which a drawing uses is a non-negotiable engineering skill.

Key Concepts

  • Projectors: parallel lines from object to plane, always perpendicular to it.
  • Principal planes: VP (vertical plane) catches the front view, HP (horizontal plane) the top view, PP (profile plane) the side view.
  • First-angle: object between observer and plane; each view projects onto the plane behind it. Symbol: truncated cone, circular face on the left.
  • Third-angle: plane between observer and object; each view projects onto the plane in front. Symbol: truncated cone, circular face on the right.
  • First-angle layout: top view BELOW front view; left side view on the RIGHT, right side view on the LEFT.
  • Third-angle layout: top view ABOVE front view; left side view on the LEFT — each view on its own side.
  • Convention: India/Europe (BIS/ISO) use first-angle; USA/Japan use third-angle — check the title-block symbol.

How It Works

Placing the three views of a block (first-angle), step by step:

  1. Draw the front view first — the most informative face — as the anchor of the sheet.
  2. Project down: draw the top view directly below, edge-aligned — first-angle puts it underneath.
  3. Project across: draw the left side view to the right of the front view, top-aligned.
  4. Add dashed hidden lines for invisible edges and centre lines for holes; dimension each feature once, where its shape is clearest.

Worked Example

Lay out the first-angle views of a 60 × 40 × 30 mm block, with 20 mm gaps:

  1. Front view: 60 × 40 rectangle — draw it with its lower-left corner at (0, 0), so it spans x: 0–60, y: 0–40.
  2. Top view: 60 × 30 rectangle (width × depth) — placed below with a 20 mm gap: y from −50 to −20, x still 0–60, vertically aligned.
  3. Left side view: 30 × 40 rectangle (depth × height) — placed to the right with a 20 mm gap: x from 80 to 110, y still 0–40, horizontally aligned.

Widths align vertically (60), heights horizontally (40) — that alignment is the self-check: edges must project straight across.

Common Misconceptions

  • "The two angles give different views." No — the views are identical; only their positions on the sheet swap.
  • "Side view always goes on the same side you looked from." True only in third-angle; in first-angle each side view sits on the opposite side — the single most misread rule in exams.
  • "Hidden lines are optional decoration." They are mandatory: without dashed hidden lines, interior features like blind holes simply do not exist on the drawing.

Real-World Applications

  • Manufacturing drawings: every machined part, from a bolt to an engine block, is made from orthographic views with dimensions and tolerances.
  • Architecture: plans, elevations and sections of buildings are orthographic projections.
  • PCB and sheet-metal design: flat-pattern and board layouts rely on true-shape views.

Orthographic projection flattens 3D objects into true-shape front, top and side views. First-angle nests the object between observer and plane (top view below, side views swapped); third-angle puts the plane between (views on their own sides). Read the cone symbol, align every edge, and the drawing becomes a buildable part.

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