Chapter 4. Technical Drawing and Plan Reading

Drawings are the common language of technical work. They tell the maker what to build, how big, from what, and to what accuracy [9].

Types of drawings

Orthographic projection: separate views (front, top, side) of an object.

Isometric and pictorial drawings: a single view that shows depth.

Sectional views: show internal features by “cutting” the object.

Assembly drawings show how parts fit together; detail drawings give full dimensions of each part.

Schematics: diagrams for circuits, plumbing or hydraulic systems using standard symbols.

Building plans: floor plans, elevations, sections and site plans.

Line types. Thick continuous lines show visible outlines; thin lines show dimensions and projections; dashed lines show hidden features; chain lines show centrelines and cutting planes [9].

Scale. A scale such as 1:50 means 1 unit on the drawing represents 50 units on the real object. Always check the scale and units on a drawing before measuring.

Dimensions and tolerances. Dimension lines and numbers show sizes; notes give materials, finishes and tolerances. Never scale a measurement from a drawing unless told to; use the stated dimension.

Title block. Contains the drawing title, number, scale, date, author, material and revision. Always use the latest revision.

Computer-aided design (CAD). Software draws parts and assemblies in 2D and 3D, allowing quick changes and direct links to machines [9][14].

Review: On a 1:20 drawing, a wall measures 150 mm. What is its real length? (Answer: 150 × 20 = 3,000 mm, or 3 m.)