1. Scales and lines used in drawings

2. 1 Scales Scales use ratios that permit measurements on a drawing or model to relate to the real dimensions of the actual job.

3. 2 Scales Why are working drawings produced to a scale? It is impractical to draw buildings, plots of land and most parts of a building to their full size, as they simply will not fit on a sheet of paper. Instead they are normally drawn to a smaller size, which has a known scale or ratio to the real thing – these are then called scale drawings.

4. 3 Scales What are the main scales used in the construction industry? 1 : 1; 1 : 5; 1 : 10; 1 : 20; 1 : 50; 1 : 100; 1 : 200; 1 : 500; 1 : 1250; and 1 : 2500. The ratio shows how much smaller the plan or model is to the original. We say 1 : 10 is a ratio or scale of ‘1 to 10’ or sometimes ‘1 in 10’.

5. Scales This represents a 1 m length drawn to various scales. 4

6. 5 Scales In a 1 : 10 scale drawing, 5 mm would represent 50 mm. It is simply a matter of multiplying the scale measurement by the scale ratio. 5 mm × 10 = 50 mm

7. 6 Scales What would these represent? 1.50 mm at a scale of 1 : 20 1000 mm or 1 m 2.70 mm at a scale of 1 : 100 7000 mm or 7 m 3.25 mm at a scale of 1 : 1250 31 250 mm or 31.250 m

8. 7 Scale rules Scale rules are used to save calculating the actual size represented on drawings. These have a series of marks engraved on them so that dimensions can be taken directly from the rule.

9. 8 Scale rules Scale rules can be useful, but preference should always be given to written dimensions on drawings. Mistakes can be made due to the dimensional instability of paper at different moisture contents or a fold in the paper might make it impossible to get an accurate size.

10. 9 Lines used on drawings Different line types and thickness (weights) are used on drawings for specific purposes. Do you know what these are used for? Line typeUsed for Main outlines General details and outlines Construction and dimension lines Breaks in the continuity of a drawing Pipe lines, drains and services Centre lines Showing the position of a cut (the pointers indicate the direction of view) Showing details that are not visible Showing the distance between two points

11. 10 Lines used on drawings Can you identify these lines? A thick solid line to indicate vertical section. Broken lines to indicate hidden detail.

12. 11 Lines used on drawings Thin solid dimension lines. Break lines to indicate that the object has not been drawn to its full length. How about these?