1. Dimensioning Through an Object
Dimensioning Guidelines
Virtual Academy
Dimensioning Through an Object
Whenever possible, avoid sending an extension line through an object view.
Incorrect
If it can be avoided, place dimensions to the side of an object view that will not require extension lines to run through that view.
However, it should be realized that this is not always avoidable; especially with objects that have relatively complex geometries.
Whenever two guidelines appear to conflict, the dimensioning method that most clearly identifies the size information should be used.
Project Lead The Way, Inc.
Copyright 2007

2. Crossing Extension Lines
Dimensioning Guidelines
Virtual Academy
Crossing Extension Lines
Whenever possible, avoid crossing extension lines.
Incorrect
Though it is not always avoidable, crossing extension lines can make a drawing confusing to interpret.
Whenever possible, place the dimensions on multiple views to eliminate this problem.
However, do not adopt a solution that violates the contour rule, or has the dimension placed in such a way that the extension lines are made to run through the object.
Project Lead The Way, Inc.
Copyright 2007

3. Crossing Dimension Lines
Dimensioning Guidelines
Virtual Academy
Crossing Dimension Lines
Never cross a dimension line with another dimension line or an extension line.
Incorrect
There is no situation for which crossing dimension lines constitutes an appropriate dimensioning technique.
Recognize that the smallest dimensions occur closest to the object, with each successively larger dimension occurring outward. This helps to avoid the problem of crossing dimension lines.
Project Lead The Way, Inc.
Copyright 2007

4. Dimensioning Guidelines
Virtual Academy
Leader Line Conventions
Leader Line Definition
Leader Line Angles
Diameter versus Radius
Hole and Cylinder Dimensions
The next section of this lesson will explore what leader line dimensions are, where they are used, how they are applied to drawings, and their most common uses.
Project Lead The Way, Inc.
Copyright 2007

5. Dimensioning Guidelines
Virtual Academy
Terminology
Leader
A leader is a thin, solid line used to indicate features with which a dimension, note, or symbol is associated.
Points toward the center of the feature
Arrow on one end touches the part or detail
Text is extended from a short horizontal line or “shoulder” on the other end
A leader line is a special kind of dimension that is used to identify the size of geometric features, such as hole or cylinder diameters, chamfer sizes, thread types, and radius values.
Leader lines are accompanied by dimension values or notes.
They are similar to dimension lines, in that they have an arrow. But unlike a dimension line, a leader line arrow actually touches the feature to which it is referring.
Project Lead The Way, Inc.
Copyright 2007

6. Dimensioning Guidelines
Virtual Academy
Leader Line Angles
Whenever possible, a leader line dimension should occur at approximately 30°, 45°, or 60° from the horizontal or vertical.
Leaders should never be drawn horizontally or vertically
To keep a dimensioned drawing looking neat, leader lines should be placed at either 30°, 45°, or 60° angles to the horizontal or vertical.
Project Lead The Way, Inc.
Copyright 2007

7. Diameter versus Radius
Dimensioning Guidelines
Virtual Academy
Diameter versus Radius
A complete circular object is called out by its diameter.
A fillet or arc is identified by its arc radius.
Circles and cylindrical objects are always dimensioned by diameters.
A diameter is the distance across a circle, and is measured through the center of a circle.
Arcs, or partial circles, are identified by their radius values.
A radius is the distance from the center of an arc or circle to any point on its edge.
Project Lead The Way, Inc.
Copyright 2007

8. Hole and Cylinder Dimensions
Dimensioning Guidelines
Virtual Academy
Hole and Cylinder Dimensions
A hole is dimensioned on a view showing its true circular shape. A leader should be used for this purpose.
A cylinder, or solid cylindrical feature, is dimensioned on a side view using a linear dimension.
As previously stated, circles are always dimensioned by their diameter values. This is true whether the circle represents a cylindrical shaft of space, such as a hole, or a solid cylindrical object, such as an axle.
A hole diameter is called out using a leader line, whereas a solid cylindrical feature is dimensioned on its side profile using a linear dimension. In both instances, a diameter symbol is used to tell the viewer that the associated dimension is in fact a diameter value.
Project Lead The Way, Inc.
Copyright 2007

9. Dimensioning Guidelines
Virtual Academy
Common
Dimensioning
Errors
Unnecessary Dimensions
Duplicate Dimensions
Dimensioning to Hidden Lines
True Scale
The last section of this lesson will explore common dimensioning errors that are encountered, such as adding unnecessary dimensions, duplicating dimensions between views, dimensioning to hidden lines and features, and errors that sometimes occur when a scaled object is dimensioned.
Project Lead The Way, Inc.
Copyright 2007

10. Unnecessary Dimensions
Dimensioning Guidelines
Virtual Academy
Unnecessary Dimensions
A drawing must contain only those dimensions that are necessary to define the object’s geometry.
Incorrect
Over-dimensioning and omissions of critical information are common mistakes.
It takes a certain level of manufacturing knowledge to recognize how an object’s geometry is completely and appropriately defined through dimensioning. Manufacturing knowledge also helps the designer to understand that some dimensions have no bearing when it comes to actually creating a part.
The aligned dimensions that are shown in the example image do serve to define the object’s geometry, but they do not represent the simplest or most effective way. Replacing them with standard height and width dimensions would help the manufacturer avoid unnecessary calculations or assumptions.
The bottom line is, dimensions that appear on a drawing should provide a complete and appropriate geometric description of the object.
Project Lead The Way, Inc.
Copyright 2007

11. Dimensioning Guidelines
Virtual Academy
Duplicate Dimensions
Do not call out the same dimension on more than one view.
Incorrect
Another common error is dimensioning a feature more than once, by dimensioning identical features on two or more views.
Duplicate dimensions are redundant, and only add clutter to a drawing.
In the example, two of the height dimensions have been repeated on the right side view.
Project Lead The Way, Inc.
Copyright 2007

12. Dimensioning to Hidden Lines
Dimensioning Guidelines
Virtual Academy
Dimensioning to Hidden Lines
Never dimension to hidden lines. If necessary, generate an alternate view, or section view, where the feature appears as an object line.
Hidden lines are less visible than object lines, and should not be dimensioned to.
There are very few instances that you will ever encounter where it would be necessary to dimension to a hidden line.
In most cases, an alternate view should be used or created that shows the hidden feature as an object line.
If an edge or feature does not appear as an object line in any of the basic orthographic projections, then a sectional view should be created.
Project Lead The Way, Inc.
Copyright 2007

13. Dimensioning Guidelines
Virtual Academy
True Scale
Dimensions should reflect an object’s actual size; not its scaled size.
Lastly, the dimension values should always reflect the true size of the object, regardless of the scale of the drawing.
If a scaled drawing is being dimensioned, then a note indicating the drawing scale should be placed somewhere on the drawing.
Project Lead The Way, Inc.
Copyright 2007

14. Dimensioning Guidelines
Virtual Academy
References
Bertoline, G. R., & Wiebe, E. N. (2003). Technical graphics communication (3rd ed.). NY: McGraw-Hill Companies, Inc.
Lockhart, S., & Johnson, C. (2000). Engineering design communication. Upper Saddle River, NJ: Prentice Hall Inc.
Madsen D. A., Folkestad, J., Schertz, K. A., Shumaker, T. M., Stark, C., & Turpin, J. L. (2004). Engineering drawing and design (3rd ed.). Albany, NY: Delmar-Thompson Learning.
Spence, W. P. (1991). Drafting technology and practice (3rd ed.). NY: Glencoe-McGraw Hill Inc.
Wallach, P. (2003). Fundamental of modern drafting. Clifton Park, NY: Thomson Delmar Learning.
Now that you know proper dimensioning guidelines you can create drawings that are easily read and understood.
Project Lead The Way, Inc.
Copyright 2007

15. Dimensioning Guidelines
Virtual Academy
Credits:
Writer: Terry C. Nagy Jr.
Lesson Editor: Ed Hughes
Narration: CJ Amarosa
Production: CJ Amarosa
We would like to thank you for joining us for this lesson on dimensioning guidelines. We hope it was helpful and your Virtual Academy learning experience enjoyable.
Project Lead The Way, Inc.
Copyright 2007