Technical Drawing, Diagrams and Schematics
What this domain tests
Technical Drawing, Diagrams and Schematics checks whether you can read and interpret engineering information: orthographic views, scale, dimensions, tolerances, line types, and electrical or mechanical symbols. You must extract the intended size, shape, or connection without seeing the real object.
Core rules
- Third-angle projection places the top view above the front view and the right-side view to the right; first-angle places the top view below and the right-side view to the left.
- Visible edges are continuous lines; hidden edges are dashed; centrelines are chain lines.
- A scale 1:20 means drawing length = actual ÷ 20. To find actual, multiply the drawing measurement by 20.
- Dimensions show true size regardless of drawing scale. Do not scale a dimensioned drawing with a ruler unless no dimension is given.
- In schematics, a dot at a crossing means a connection; no dot means the lines cross without joining.
- Tolerances give permitted variation; a fit is not interchangeable unless the limits overlap correctly.
Worked example
A drawing at scale 1:50 shows a dimensioned feature as 36 mm. What is the actual length? The scale ratio is drawing:actual = 1:50, so actual = 36 × 50 = 1800 mm = 1.8 m. If the same feature were measured on the paper as 36 mm but the drawing said 'do not scale', you would still use the printed dimension, not the ruler. Check the unit note: drawings may be in millimetres even when the object is metres long.
Traps
- Multiplying by the scale when the drawing is already larger, or dividing when it is smaller.
- Mixing first-angle and third-angle view positions.
- Treating a crossing without a dot as a junction.
- Ignoring 'typical' or tolerance notes and assuming an exact nominal size.