Engineering drawing relies heavily on precise lines to convey accurate information about the dimensions, shape, and features of mechanical components, structures, and systems. Different types of lines are used in engineering drawings to represent various elements and details clearly and consistently. This standardization ensures that the drawings can be universally understood by engineers, architects, and construction professionals. Here is an in-depth exploration of the different types of lines used in engineering drawings, their purposes, and conventions.
1. Visible or Object Lines
Visible lines, also known as object lines, are used to outline the visible edges of objects. These lines are solid and thick, typically around 0.6 mm in thickness, and they form the main shape of the object being drawn. They represent all the edges that are visible from the viewing angle and are crucial for understanding the overall form of the object.
2. Hidden Lines
Hidden lines represent edges and boundaries that are not visible from the current viewing angle. These lines are typically drawn as short dashes, with a standard dash length of about 2-3 mm and a gap length of around 1 mm. The thickness of hidden lines is usually thinner than visible lines, often around 0.35 mm. They help in visualizing the internal features of an object that are obscured by the external surfaces.
3. Center Lines
Center lines are used to denote the centers of circles, arcs, and symmetrical parts. These lines are drawn as alternating long and short dashes, with the long dashes being about 10-20 mm and the short dashes about 2-3 mm. The thickness is generally around 0.35 mm. Center lines are crucial for aligning and placing components accurately, as well as for marking the axes of symmetrical objects.
4. Dimension Lines
Dimension lines are used to indicate the measurements of an object. They consist of a solid line with arrowheads at both ends, pointing to the exact locations being measured. The actual measurement is written above the dimension line. These lines are usually thin, around 0.25 mm in thickness, to avoid cluttering the drawing while still being easily readable.
5. Extension Lines
Extension lines extend from the edges of an object to the dimension lines, showing the exact points between which the dimensions apply. They do not touch the object but start a short distance away from it. Extension lines are also thin, around 0.25 mm, and ensure clarity by indicating precisely where measurements are taken from.
6. Leader Lines
Leader lines are used to connect a note, dimension, or symbol to a particular feature on the drawing. These lines are usually thin, around 0.25 mm, and are drawn at an angle to avoid confusion with other types of lines. Leader lines end with an arrowhead or dot pointing to the feature they are describing.
7. Section Lines
Section lines, or crosshatch lines, are used in sectional views to indicate the surfaces that have been cut through. These lines are typically drawn at a 45-degree angle and are evenly spaced. The spacing and thickness can vary depending on the material being represented and the scale of the drawing, but they are generally thin, around 0.25 mm.
8. Break Lines
Break lines are used to indicate that a portion of the object is not shown in the drawing, either to save space or because the section is repetitive and does not require full illustration. There are two types of break lines: long break lines, which are freehand zigzag lines, and short break lines, which are solid, usually wavy lines. Both types are drawn thin, around 0.25 mm.
9. Phantom Lines
Phantom lines, also known as datum or reference lines, represent features that are not part of the object but are related to it, such as paths of movement or positions of interchangeable parts. These lines are drawn as long dashes alternating with two short dashes. They are typically thin, around 0.25 mm.
10. Cutting Plane Lines
Cutting plane lines are used to show where an object has been cut to create a sectional view. These lines are thick, around 0.6 mm, and are drawn with alternating long and short dashes. Arrowheads on the ends of the cutting plane line indicate the direction of sight for the sectional view.
11. Chain Lines
Chain lines are used to indicate the positions of repeated details, such as gear teeth or bolt holes. They consist of a series of long and short dashes, similar to phantom lines but usually slightly thicker, around 0.35 mm.
12. Guide Lines
Guide lines, also known as construction lines, are very light and thin lines used to help construct and align other features of the drawing. They are usually drawn freehand and are not intended to be part of the final drawing. These lines are extremely thin, around 0.18 mm, and are often erased after the final lines are drawn.
13. Border Lines
Border lines define the boundaries of the drawing sheet. They are usually the thickest lines on the drawing, around 0.8 mm, and help to frame the entire drawing area.
Standards and Conventions
The use of these lines follows specific standards and conventions to ensure consistency and readability. The most widely adopted standards are set by organizations such as the International Organization for Standardization (ISO) and the American National Standards Institute (ANSI). These standards specify the types of lines, their thicknesses, and the styles to be used in engineering drawings.
Applications and Importance
Different types of lines are fundamental to creating accurate and informative engineering drawings. They help convey complex information about the shape, size, and features of objects clearly and concisely. Each type of line has a specific purpose, ensuring that the drawing can be interpreted correctly by anyone familiar with the standards. This precision is crucial in fields such as mechanical engineering, civil engineering, architecture, and manufacturing, where accurate drawings are essential for constructing parts and structures.
In summary, the types of lines used in engineering drawing serve as a universal language that allows engineers, architects, and construction professionals to communicate detailed information effectively. By adhering to standardized line types and conventions, drawings can convey the necessary information to fabricate, construct, and inspect components and structures accurately. Understanding and applying these different types of lines is a fundamental skill for anyone involved in technical drawing and design.