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Dimensioning

Dimensions Dimensions are used to describe the sizes and

relationships between features in your drawing. Dimensions are used to manufacture parts and to

inspect the resulting parts to determine if they areacceptable.

Drawings with dimensions and notes often serve asconstruction documents and legal contracts.

ANSI Y14.5M-1994 is the current standard. Otherstandards may apply.

Standards for Your Career Field Standards are different in

different career areas.

Most of the examples in thiscourse will be of mechanicalparts.

Civil, Electrical, Construction,and other areas follow similarpractices, but sometimes withless need for precision inmeasurements.

Dimensioned drawings are apart of a contractual document.

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Dimension TypesDimension Types

Size dimensions

Describe size of features such as holes

Do not require datum surfaces

Location dimensions

Provides location of one surface or featurein relation to another

Requires a datum surface for reference

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FeaturesFeatures VocabularyDimension line, Extension line, Leader,

Dimension offset or gap, Centerline,

Finish mark, Dimension value

Baseline dimensioning, Chained dimensioning

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Tolerance

Definition: The total allowable variation

an acceptable part can have from thespecified dimension.

The less variation allowed, the morethe part will cost to make.

3 Things for Good Dimensioning

Good technique of dimensioning

Good choice of dimensions

Good placement of dimensions

Dimensioning Technique

describes how the dimensions in yourdrawing should look.

defined by various standards like ANSIY14.5-1994.

help you create dimensions that are plainlyvisible and can be easily interpreted.

specifies sizes for creating dimensionsrelative to the paper size of your final plot.

Dimensioning Symbols

Leaders Orientation for Dimension Values

Unidirectional:

read horizontally from bottom of sheet

Aligned: align with dimension line and read from

bottom or right side of sheet

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Unidirectional Orientation Aligned Orientation

Aligned Dimensions Stagger Dimension Values

Dimension& ExtensionLines

Finish Marks

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Choice of Dimensions the dimensions you specify determine the

way the the part is manufactured and theway the tolerance is applied

consider the purpose of the part and itsfunction in the assembly

consider how easy it will be to check themeasurement on the actual part

fully dimension each part

do not over dimension, each dimensionshould appear only once

Choosing Which Dimensions to Show

Dont overdimension

Give the diameter ofcircular shapes, theradius of arcs.

No redundant orsuperfluousdimensions

Give sizedimensions forfeatures.

Give locationdimensions to showhow features relateto one another.

Mating Dimensions Effect of Tolerance on Dimensioning Baseline

each dimension isspecified from a commonbaseline

tolerances do not stack

Chained

each dimension continuesfrom the previous one

tolerances stack

Units

Fractional Inch

Decimal inch dimensions are

typically specified to 2 decimalplaces.

Metric values are typically given in

whole millimeters or to one decimalplace.

Placement of Dimensions

Rules-of-thumb for dimension placement helpensure that others will be able to interpret yourdrawing

Where placement practices conflict, rememberthat your goal is to clearly communicatethepurpose of the drawing. Use the practice you feelwill make the drawing easy to understand.

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Placement Practices Avoid dimensioning on

object. Avoid dimensioning to

hidden lines.

Place dimensionsbetween views whenpossible.

Dont floatdimensions.

Group dimensionsaround a central view.

Place dimensions

where feature showsshape.

Dimension from orbetween machinedsurfaces

Give overall dimensionswhere possible.

Dont dimension torectangular viewcenterlines.

Dimensioning Prisms

Dimensioning Cylinders Dimensioning Holes

Using Diameter SymbolLocating Holes

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Coordinate (Ordinate)

DimensioningSummary

Good dimensioning is a combination of choosing

dimensions which reflect your design intent, propertechnique in creating the details of the dimensionline, extension line, arrowheads and dimensionvalues, and placing the dimensions on the drawing sothat they can be read clearly.

Dimensioning drawings correctly can be as importantor more important than drawing the shapes correctly.

Good dimensioning requires practice and thought!

Where to get more informationWhere to get more information

Refer to examples in your textbook

ASME, ANSI, ISO, and other organizationspublish standards.

Talk to people in manufacturing. Theirexperience is valuable in helping you keepthe cost of the product down by specifyingreasonable tolerances and up-to-datemanufacturing processes.