Technical drawing: from sketch to working drawing

As a technical designer your drawing is a legal and technical document. The person building or producing from your drawing must be able to read exactly what you meant — without guessing. Therefore technical drawing follows a common language of projection methods symbols line types and dimensioning rules described in standards.

§The most important drawing types

A project rarely consists of one drawing. Different drawing types answer different questions and a technical designer must know when each type is used.

• 01Overview and situation plans: show relationships, placement and context on a large scale.
• 02Plan, section and facade drawings: the classic building drawings showing the building seen from above, cut through and from outside.
• 03Detail drawings: zoom in on an assembly or node where high precision is needed.
• 04Component and working drawings: show a single part with all dimensions so it can be manufactured.
• 05Assembly drawings: show how multiple parts are assembled into a whole.

§Projection and views

To show a three-dimensional object on flat paper rectangular projection is used where the object is seen from different sides. The views are placed according to a fixed method so the reader knows which side is shown where. In Europe first angle projection is typically used while third angle projection is more common elsewhere — the projection symbol in the drawing header tells which method applies.

§Objectives that cannot be misunderstood

Dimension notation is often where errors occur. A good rule is that each dimension should only appear once and that dimensions should be set from a logical reference edge or zero point so dimension accumulation is avoided. Dimensions should be placed outside the part itself when possible, and dimension arrows, reference lines and text should not cross each other unnecessarily.

• 01Use a continuous reference (baseline), not a chain of measurements, when precision is critical.
• 02Avoid redundant dimensions—the item must not be over-constrained.
• 03Specify tolerance specifications and surface requirements where they belong.
• 04Keep text size and arrowheads uniform throughout the drawing set.

§Line types and symbols

Line types have fixed meaning: a heavy solid line is visible edges, a dotted line is hidden edges, a thin dash-dot line is center lines, and a thin solid line is used for dimension and reference lines. When line types are used consistently, a professional can read the drawing without explanation.

“A drawing is not finished until there is nothing left to remove — not when there is nothing left to add.”

— Principle of drawing clarity