Topic 05- Line Types and Dimensions in Engineering drawing

Introduction to lines

The article talks about Line Types and Dimensions in Engineering drawing. The most fundamental parameter to define any engineering design is a point. The set of these points is called a line. Just as the points can be arranged in a number of fashions. This gives rise to number of important line types. These will be discussed shortly.

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Important Line Types

Some of the important Line types are elaborated below

Object Line

Object lines are thick, solid lines that are used to represent the visible edges or surfaces of an object. They are drawn to show the outline of the object and its features in a particular view. Object lines are the most important lines in a drawing as they define the shape and form of the object.

Hidden Line

Hidden lines are thin, dashed lines that are used to represent edges or surfaces that are not visible in a particular view. They are drawn to show the features that are hidden behind the visible parts of the object. Hidden lines are important as they help to convey the shape and size of the object accurately.

Extension Line

Extension lines are thin lines that are used to indicate the extent of a feature to which a dimension is attached. They extend from the object line and terminate in a break or arrowhead, and are used to guide the dimension line.

Dimension Line

Dimension lines are thin lines with arrows at each end that are used to indicate the size or location of a feature on the drawing. They are drawn between two extension lines that extend from the object line and terminate in arrowheads. The dimension value is usually placed above the dimension line and is accompanied by a unit of measurement.

Leader Line

Leader lines are thin lines with an arrow or dot at one end that are used to indicate the location or size of a feature. They are used when a dimension cannot be placed adjacent to the feature and are drawn from the feature to the dimension line or note.

Centre-Line

Center lines are thin, alternating long-short-long dashed lines that are used to indicate the center of symmetry or axis of rotation of a part. They are used to define the center of cylindrical features, such as holes or bosses, and to indicate the location of a feature that is symmetrical about its center line.

Symmetry Lines

Symmetry lines are used in technical drawing to indicate the axis of symmetry of a part or feature. They are drawn as a centerline with two thick, perpendicular track marks at each end. Symmetry lines are useful in conveying information about the symmetry of a part, and they help the viewer understand the orientation and location of features that are symmetric about an axis. Symmetry lines are commonly used in drawings of mechanical parts, where symmetry is often an important design consideration.

Note

It’s important to note that some lines in an engineering drawing have higher precedence than others. For example, leader lines and dimension lines are typically more important than extension lines and other types of lines because they convey critical information about the size, shape, and location of features in the drawing. As such, it’s important to pay close attention to the placement, style, and spacing of these lines to ensure that the final drawing is accurate and easy to read. Some lines have higher precedence than others according to their importance in the final drawing.

Introduction to dimensions

The next important thing is the method of dimensioning. An object is made up of lines. We can easily draw lines of an object, but we need dimensions to compare them quantitatively. Hence there are some types of dimensioning and there are some rules that we have to keep in mind while writing about dimensions.

Dimension

Dimensions are an essential aspect of engineering drawing, used to communicate the size and location of different features on a technical drawing. Accurate dimensioning is crucial for ensuring that parts fit together correctly and that the design functions as intended. In this article, we’ll discuss the two main types of dimensioning used in engineering drawing: aligned and unidirectional.

Types of dimensioning

There are two main types of dimensioning. These are aligned and unidirectional.

Aligned system

Aligned dimensioning is the most common type of dimensioning used in engineering drawing. In this method, dimensions are written perpendicular to the dimension line so that they can be read from the bottom or right-hand side of the paper. The dimension lines are placed in the middle and on top of the dimension lines. Aligned dimensioning is useful for presenting multiple dimensions in a clear and organized way, especially in complex drawings.

Unidirectional system

Unidirectional dimensioning is an alternative method of dimensioning that is sometimes used in engineering drawing. In this method, dimensions are placed in such a way that they can be read from the bottom edge of the drawing sheet only. Unidirectional dimensioning is useful for drawings with limited space or for drawings that require a more compact layout. It is also used in industries such as architecture, where the standard practice is to use unidirectional dimensioning.

Dimensioning Rules

There are some basic rules that engineers should follow when dimensioning a technical drawing:

1. Place dimensions outside of the object whenever possible to avoid cluttering the drawing.
2. Avoid placing dimensions on hidden lines, as this can make them difficult to read.
3. Use a consistent style for all dimensions, including text size, arrowheads, and line thickness.
4. Use the same units of measurement throughout the drawing, and use appropriate tolerances for each dimension.

Conclusion

Dimensioning is a fundamental part of engineering drawing, used to communicate the size and location of different features on a technical drawing. Engineers should be familiar with the different types of dimensioning and the rules for dimensioning a drawing to ensure accuracy and clarity.

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