Lines of different types and thicknesses are used for graphical representation of objects. The types of lines and their applications are shown in below table. Typical applications of different types of lines are shown below.
Thickness of Lines
Two thicknesses of lines are used in draughting practice. The ratio of the thick to thin line should not be less than 2:1. The thickness of lines should be chosen according to the size and type of the drawing from the following range:
0.18, 0.25, 0.35, 0.5, 0.7, 1, 1.4 and 2
It is recommended that the space between two parallel lines, including hatching, should never be less than 0.7 mm.
Order of Priority of Coinciding Lines
When two or more lines of different types coincide, the following order of priority should be observed:
- Visible outlines and edges (Continuous thick lines, type A),
- Hidden outlines and edges (Dashed line, type E or F),
- Cutting planes (Chain thin, thick at ends and changes of cutting planes, type H),
- Centre lines and lines of symmetry (Chain thin line, type G),
- Centroidal lines (Chain thin double dashed line, type K),
- Projection lines (Continuous thin line, type B).
The invisible line technique and aixs representation should be followed as per the recommendations given below.
Termination of Leader Lines
A leader is a line referring to a feature (dimension, object, outline, etc.).
Leader lines should terminate,
- with a dot, if they end within the outlines of an object,
- with an arrow head, if they end on the outline of an object,
- without dot or arrow head, if they end on a dimension line.
It is common practice to omit hidden lines in an assembled view, when their use tends to confuse an already complex drawing or when the feature is sufficiently clear in another view; but it is not advisable for a beginner to do the same and he will have to show the hidden lines in his drawing practice.