16.2 Lines
Cameron Kjeldgaard
Lines are the simplest element of any print, being able to distinguish between the different types of lines and identify their purpose is absolutely essential to interpreting any drawing. Some lines may have very niche uses in specific industries or to particular individuals within an industry, the most common will be described here.
Lines on prints don’t follow the standard mathematical definition of a line as a straight one-dimensional figure. Lines serve a variety of purposes, some represent the physical edges of what is being made, some act as a reference point for different views, some are used for dimensioning and measurement. With so many lines there must be a way to distinguish them, some lines are straight and solid, others may be drawn irregularly or broken into various series of dashes. The thickness of a line is also often significant, a line may be fine, medium, or thick; this is called the line weight. Depending on the quality of the print and the detailing work that went into making it, line weights may a be more or less reliable way to differentiate lines.
- An object line represents the physical edge of an object as it would be seen from that view in the drawing.
- A hidden line also represents the physical edge of an object, but one that would not be visible from that view in the drawing, because it is obscured from view by another part of the object being shown.
- A phantom line is used to represent the different possible positions of any moving parts of any assembly.
- Extension lines show the reference points on the object from which dimensions are given. Extension lines may be longer or shorter to make good use of the space available on the print.
- Dimension lines end in arrows which connect to extension, they show the extent of a given dimension.
- Centerlines aid in providing dimensional information about an object. They are used to show the center of symmetrical objects, as well as circles, arcs, and radii. A centerline showing the center of any circular object may appear as a “+” sign called a center mark.
- A leader line points to a specific part of the object being shown to dimension it or add a written direction or note. If referencing an edge the leader line will end in an arrow, but a solid dot is used when referencing a surface.
- Both short break lines and long break lines are used to conserve space on a drawing. If there is some stretch of an object being built that doesn’t require attention from the fabricator there isn’t any reason to show it on the print. The portion of the object omitted will be long or short depending on the style of the line.
- A cutting plane line is used as a reference point to interpret a section view. The arrows on the cutting plane line indicate the perspective of the related view. The letters at either end of the cutting plane line are the name of the related view. For example a cutting plane line with A at either end would reference you to a view labeled “A-A”.
Attributions
- Figure 16.1: Various Types of Lines Used in Welding Blueprints by Nicholas Malara, for WA Open ProfTech, © SBCTC, CC BY 4.0
- Figure 16.2: Symbol for Centerline by Nicholas Malara, for WA Open ProfTech, © SBCTC, CC BY 4.0
The thickness of a line; most line weights are fine, medium, or thick.