Line styles and thicknesses are an important component of instrumental drawing. They can indicate the boundaries of a part, a part's hidden features, or the travel path of a machinist's drill, mill or lathe. It is important that the correct line style and thickness is used to ensure your instrumental drawing is not ambiguous to anyone involved in the manufacture or construction of a product or environment, the production of instructions or the use of the product or environment. The advantage of changes line thicknesses can be seen when a drawing requires lots of dimensions, the thicker outline stands out from thinner dimension lines.
Line Styles and Thicknesses
|Continuous - Thick||
To indicate visible outlines
|Continuous - Thin||
Fictitious internal lines
|Continuous - Dashed||Hidden Features|
|Chain line - Thin||Centrelines
Material for removal
|Chain line - Thick at ends and at change of direction||To indicate a cutting plane for sectioned views|
The thickness of lines are based on the size of the drawing sheet using used. The table below shows the appropriate line thicknesses applicable to the various sheet sizes.
|Sheet Size||Line Type and Thickness (mm)|
|A2, A3, A4||0.35||0.18||0.18||0.18||0.18||0.25||0.18||
Line Presentation in Technical Drawings
The presentation of lines in instrumental drawings is important as it maintains clear communication of intention and avoids ambiguity. It is therefore important that the following guidelines are used when drawing the applicable line styles;
The scale of line thickness and length of dashes and spaces should be uniform across a drawing.
The thickness of line(s) used should not become thinner than 0.18mm if the drawing sheet was reduced to A4
When indicating centre points, centreline dashes should intersect at the origin of the feature
Centrelines should extend a small distance past the feature of the drawing
Centrelines should cease at any other line of the drawing
Chain lines that indicate a cutting plane should begin and end with long dashes as best fits the drawing
Chain lines that form an angle should cross or meet at the corners
Dashed lines should start and end with dashes in contact with the visible or lines from which they originate
If a dashed line meets a curved line tangentially, then it should be with a solid portion of the line