Dimensioning Guidelines

Dimensioning

Terminology

The process of describing the size of an object, and locating important features of the object.

Dimension Amount

Dimension Line

Extension Line

Dimension Line

Terminology

A dimension line is a thin line drawn perpendicular to extension lines with arrowheads at each end.• indicates linear

distance between object edges and locates features such as holes.

Green Lines

The first dimension lines should be placed 3/8” from the object, with each successive dimension line spaced ¼” apart.

Dimension Line Geometry

All dimension values should be oriented parallel to the bottom edge of the paper, and should read left-to-right (unidirectional).

Unidirectional Dimensions

Correct

The example below is incorrect because the numbers are oriented towards the right side of the page.

Unidirectional Dimensions

Incorrect

TerminologyExtension LineAn extension line is a thin solid line that is drawn perpendicular to a dimension line.

• extends an object line or centerline

• shows the extents of a dimension

Green Lines

Extension lines start about 1/16” from the object, and extend about 1/8” past the last dimension.

Extension Line Geometry

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116

Object

Object lines should never be used as an extension line. Dimensions lines must terminate on extension lines.

Object Lines as Extension Lines

Incorrect

If properly placed, dimensions will appear to taper from largest to smallest. The largest dimensions should occur furthest away from the object.

Dimension Placement

Dimensions should be placed on the view that best illustrates the shape or contour of the feature.

Contour (Shape) Dimensioning

Incorrect

Dimensions should be placed on the view that best illustrates the shape or contour of the feature.

Contour (Shape) Dimensioning

Correct

In most cases, dimension values should be centered on their dimension lines or between their extension lines.

Centering Dimension Values

Incorrect

Whenever possible, dimensions should be placed in the space between the front, right side, and top views.

Dimensioning Between Views

Incorrect

Do NOT place dimensions within the object. Always locate dimensions outside of the object.

Dimensioning Within an Object

Incorrect

Whenever possible, avoid sending an extension line through an object view.

Dimensioning Through an Object

Incorrect

Whenever possible, avoid crossing extension lines.

Crossing Extension Lines

Incorrect

Never cross a dimension line with another dimension line or an extension line.

Crossing Dimension Lines

Incorrect

Leader Line Conventions

• Leader Line Definition• Leader Line Angles• Diameter versus Radius• Hole and Cylinder Dimensions

TerminologyLeader

• 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 is a thin, solid line used to indicate features with which a dimension, note, or symbol is associated.

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

Leader Line Angles

A complete circular object is called out by its diameter.

A fillet or arc is identified by its arc radius.

Diameter versus Radius

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.

Hole and Cylinder Dimensions

Common Dimensioning

Errors

• Unnecessary Dimensions• Duplicate Dimensions• Dimensioning to Hidden Lines• True Scale

A drawing must contain only those dimensions that are necessary to define the object’s geometry.

Unnecessary Dimensions

Incorrect

Do not call out the same dimension on more than one view.

Duplicate Dimensions

Incorrect

Never dimension to hidden lines. If necessary, generate an alternate view, or section view, where the feature appears as an object line.

Dimensioning to Hidden Lines

Dimensions should reflect an object’s actual size; not its scaled size.

True Scale

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.

References

Writer: Terry C. Nagy Jr.

Lesson Editor: Ed Hughes

Narration: CJ Amarosa

Production: CJ Amarosa

Credits: