Four Types of Lines Used in Drawing
Certain features on a Engineering Drawing requires specific ways of indication. For example, holes require center lines to identify the center and show that it is round. Hidden detail are shown with a certain line type to avoid confusion with visible edges.
Most CAD Software packages will have these different line types predefined as layers. Depending on the layer chosen, the line will display it in a certain way. Often, most drafting companies will have their own custom layers with different colours, however the final product on paper will (or should) be as discussed below.
| Line | Description |
 | Continuous Thick Line |
 | Continuous Thin Line |
 | Continuous Thin Freehand Line |
 | Continuous Thin Zigzag Line |
 | Thick or Thin Dashed Line |
 | Thin Chain Line |
 | Thin Chain Line with Thick ends |
 | Thick Chain Line |
 | Thin Chain Double Dashed Line |
Continuous Thick Line
The continuous thick line is used to show visible outlines or edges of a component or assembly. This line may be made thin if the drawing is congested and allot of lines are so close to each other that the clarity of the drawing is negatively influenced.
Continuous Thin Line
The continuous thin line is the most frequently used line type on Engineering Drawings. These lines are solid and has no break in them. Here is the list of cases where the continuous thin line will be used:
- Imaginary lines of intersection
- Dimension line
- Projection lines
- Leader lines
- Hatching
- Outlines of revolved sections
- Short center lines (as opposed to the chain line)
- Bending lines
Continuous Thin Freehand Line
Freehand lines shows breaks or cuts in parts or assemblies. The edge of the partial or interrupted view is indicated with a freehand line.
Continuous Thin Zigzag Line
The Continuous Thin Zigzag Line shows a break line. If a part needs to be shortened with a break for ease of visibility, a break can be made using this line. *Remember, any dimensions spanning over the break needs to have a dimension break indicated on the dimension line also.
Thick or Thin Dashed Line
The Dashed Line is used to indicate hidden details like hidden outlines and hidden edges. The dashed line may be either thick or thin, but only one type (thick or thin) should be used on a single drawing or set of drawings.
Thin Chain Line
The Thin Chain Line is used to indicate center lines, the lines of symmetry and also trajectories. Often this line is used as a point of reference on engineering drawings.
Thin Chain Line with Thick ends
Sectional cutting planes are indicated with a Thin Chain Line with Thick ends. This helps to identify the plane in which the part or assembly is cut. If the cut line is on more than one plane, the change in direction should also be indicated with thicker ends.
Thick Chain Line
A Thick Chain Line is used to indicate special requirements on a surface. This line does not form part of the geometry of the part, but is rather used to identify the surface
Thin Chain Double Dashed Line
The Thin Chain Double Dashed Line is used to show adjacent components. This is especially useful when the component has a reference to the existing components.
It is also used to show alternative or extreme positions. On drawings where bends are indicated, these lines are used to show the initial outlines before forming or bending.
One can also use this line to indicate parts or components situated in front of the cutting plane, to give reference to the part shown.
In Closing …
In Engineering Drawings, a line is not just a line. The different lines have meaning to them. The above mentioned line types are according to the requirements of ISO standards (and many other national standards).
Four Types of Lines Used in Drawing
Source: https://engineeringdrawingbasics.com/different-line-types-used-on-engineering-drawings/