Unit 4

Alphabet of Lines

Objectives

• After completing this unit, you will be able to identify and understand the meaning of the listed lines:– Object lines– Dashed lines (hidden and phantom)– Extension lines and dimension lines– Centerlines– Leaders– Cutting-plane lines

Introduction• Drawings are the language of the construction

industry – Basis of language is its alphabet– Construction drawings use an alphabet of lines

Figure 4–1. Alphabet of lines.

Object Lines

• Line weight or thickness is varied to show relative importance– Help distinguish basic shape from surface details

• Object lines are used to show object shape– All visible edges are represented by object lines

Object Lines (cont’d.)

Figure 4–2. Elevation outlined.

Dashed Lines

• Hidden lines show object edges that would not be visible– Drawn as a series of

evenly sized short dashes

– Only used for most important features

Figure 4-3. The dashed lines on this foundation plan indicate the footing.

Dashed Lines (cont’d.)

• Phantom lines show important overhead construction– Not in hidden view,

just not in view (e.g., beams on a ceiling)

Figure 4–4. The dashed lines on this floor plan indicate the edge of the roof overhang.

Dashed Lines (cont’d.)• Phantom lines may also show alternate positions• May be different weights and lengths

Figure 4–5. The dashed lines here are phantom lines to show alternate positions of the double-acting door and the door of the dishwasher.

Figure 4–6. Different types of dashed lines are used to show different features.

Extension Lines and Dimension Lines

• Extension lines:– Thin, solid lines that project from an object to

show extent or limits of a dimension• Do not quite touch the object they indicate

Extension Lines and Dimension Lines (cont’d.)

• Dimension lines:– Solid lines of the same weight as extension lines– Drawn from one extension line to the next– Dimension is lettered above the dimension line– Expressed in feet and inches– Chain dimensions are dimensions added together

to come up with one overall dimension

Extension Lines and Dimension Lines (cont’d.)

Figure 4-7. Dimension and extension lines.

Figure 4–8. Dimension line ends.

Centerlines• Made up of long and short dashes

– Show centers of round or cylindrical objects– Indicate object is symmetrical

Figure 4–9. This centerline indicates that the column isSymmetrical, or the same on both sides of the centerline.

Figure 4–10. When centerlines show the center of a round object, the short dashes of two centerlines cross.

Figure 4–11. Method of showing the radius of an arc.

Leaders

• Some construction details are too small for clear dimensioning– Dimension is shown in a

clear area of the drawing– Leader is the thin line

showing where the dimension belongs

Figure 4–12. Leaders used for dimensioning.

Cutting-Plane Lines

• Show where imaginary cut was made in section view– Usually a heavy line with long dashes and pairs

of short dashes– Typical sections are not shown

• They would be the same if drawn from an imaginary cut in most parts of the building

Cutting-Plane Lines (cont’d.)

Figure 4–14. Building section.