Introduction to Dimensioning and Tolerancing

Dr. Darrell Wallace

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General Guidelines for Dimensioning and Multiple Views

Show dimensions in the most logical viewDon’t dimension to hidden lines. If necessary, use section views.Know the difference between first angle and third angle projections and how they are interpreted.

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Normal Placement

Placement in Limited Space

Placement of Dimensions

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Dimensioning Circles and Arcs

Simple Cylinder

Stepped Shaft

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Dimensioning Radii

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Dimensioning Holes

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Counterbores and CountersinksCounterbores

Countersinks

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Dimensioning AnglesAngles can be dimensioned using either linear or angulardimensions.

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Dimensioning Equally Spaced Holes

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Specifying Hole Dimensions

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Dimensioning Hole Positions

Whenever possible, good drawing practice dictates that dimensions should be placed in a view that shows the dimensioned feature visibly (without hidden lines).

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Tabular Dimensions

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Ordinate Dimensioning

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Part Family Dimensioning

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Decimal and Fractional Dimensions

English Fractional Units are Based on Dividing Larger Units in Half

1”/2 = ½”

½”/2=1/4”

… 1/8”, 1/16”, 1/32”, 1/64”

Fractional to Decimal Conversions

1” = 1.0000” 1/16” = 0.0625”

½” = 0.5000” 1/32” = 0.0313”

¼” = 0.2500 1/64” = 0.0156”

1/8” = 0.1250” 1/128” = 0.0078”

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English vs. Metric UnitsWithin the metric system:

1 m = 100 cm = 1000 mm

.01 m = 1 cm = 100 mm

.001 m = .1 cm = 1 mm

1 (micron) = .001 mm = .000001 m

English to Metric

1 mile = 1.609 km

1 yd = .9144 m

1 in = 2.54 cm = 25.4 mm

0.001 in = .0254 mm = 25.4

Metric to English

1 km = 0.6214 mile

1 m = 1.094 yd = 39.4 in

1 cm = 0.394 in

1 mm = 0.0394 in

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TolerancesALL dimensions used to define the shape and size of a part MUST have an associated toleranceSometimes tolerances are controlled by default or “general” tolerances that apply to the entire drawing.Tolerances that are too “loose” make for parts that don’t fit or function properly.Tolerances that are too “tight” make parts unnecessarily expensive.

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Tolerance Types

Limit TolerancePlus / Minus Tolerance Bilateral Unequal bilateral Unilateral

Choice of tolerances and dimensioning schemes should be based on functional dimensioning

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Dimensional Precision

The dimensional precision implies (to some degree) what the tolerance should be:

Fractional ± 1/32” (carpentry) X.X ± 0.10 (hacksaw) X.XX ±0.010 (standard machining) X.XXX ±0.001 (careful

machining) X.XXXX ±0.0001 (grinding) X.XXXXX… … (polishing, specialty

processes)

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ProcessCapabilities

Though it is generally not recommended that you specify processes on your drawings, it is a good idea to keep in mind the costs and capabilities of the processes that will likely be used.

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The Costs of Precision

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Title Block, BOM, and Revisions

A. Title Block

B. Bill of Materials

C. Revision Block