bruce mayer, pe registered electrical & mechanical engineer bmayer@chabotcollege

[email protected] • ENGR-22_Lec-15_Dimensioning-1.ppt1

Bruce Mayer, PE Engineering 22 – Engineering Design Graphics

Bruce Mayer, PERegistered Electrical & Mechanical Engineer

[email protected]

Engineering 22

DimensionDimensioninging

Part-1Part-1



Chp.8 Learning GoalsChp.8 Learning Goals

Apply Proper/Conventional Dimensioning Standards to Adequately Describe a Physical Object (e.g., a Machined Part) Such that It may be Properly Fabricated

Use AutoCAD to add Dimensions to Standard Orthographic Projection Views in Both Dimension-Line and BaseLine Forms



DimensionsDimensions Dimensions are used to describe

the sizes and relationships between features in Technical drawings

Dimensions are used to manufacture parts and to inspect the resulting parts to determine if they are acceptable.

Drawings with dimensions and notes often serve as construction documents and legal contracts.

ANSI/ASME Y14.5M-1994 is the current standard. Other standards may apply.



Standards for Different Fields Standards are different in

different engineering disciplines. Most of the examples in this

course will be of MECHANICAL parts.

Civil, Electrical, Construction, and other areas follow similar practices, but sometimes with less need for precision in measurements.

Dimensioned drawings are a part of a contractual document.



Dim TerminologyDim Terminology

Dimension Line

Extension Line

Leader

Dimension Offset/Gap

CenterLine

Finish Mark

Dimension Value

BaseLineDims

Chained Dims



DimLine ExampleDimLine Example

Title =Drive Shaft, Pulley

Matl = SS-440C Round Bar



BaseL

ine D

im

BaseL

ine D

im

Exam

ple

Exam

ple

Title =Bottom Plate

Matl = 11Ga (0.09” thick) 5052-H32 Al



Basic Dimensioning ConceptsBasic Dimensioning Concepts

Give SIZE and LOCATION of ALL features

Size of main feature• length, height, width

Size of other features (basic shapes)• prism, cylinder, wedge, cone, sphere

Locate other features with respect to the main feature



Location & Size DimensionsLocation & Size Dimensions



Location & Size ExampleLocation & Size Example



Dimensioning PracticesDimensioning Practices

Place Dims for Maximum Legibility Choose Dims for Maximum Utility

• Depends on Fabrication Process



Dim vs Extension LinesDim vs Extension Lines

Shorter Dim Lines Closer to Object Long Dim Lines Should Not Cross “Short” Extension Lines Ext. Lines May Cross to Maintain Consistent Dim Gap Avoid Dims INSIDE the Object or Object-Envelope Dim lines should Line-up with Feature Lines (Visible,

Hidden, Center)• Need a CLEAR ASSOCIATION with Dimensioned Feature.



LeadersLeaders

Leader A Thin Solid Line From an Object-Feature to A Note or Dim-Callout

Should be an INCLINED Line• Forms a Distinct Angle with the Part Feature

Typically use a 6mm (0.25”) Horiz. Shoulder Leader to a Circle or Arc Should Be RADIAL



Nix Mixed FractionsNix Mixed Fractions Unless Required for

Some Very Unusual Reason Do NOT Use Fractional Dims• They are Effectively

Obsolete– Continue to Exist Thru

Inertia– NEVER Applied to

meter-based linear Dims



Dual DimensioningDual Dimensioning Generally Not Recommended for Fab Dwgs

• Potential for MisReading Dims

• Make Drawing Look “Busy”

Good for Overall (Layout) or “FootPrint” Drawings Used as A Communication tool

Use Brackets to Distinguish Secondary Dim

Side-by Side Over/Under



ACAD Dual Dim → Dim Styl MgrACAD Dual Dim → Dim Styl Mgr Activate Dimstyle

Mgr

Pick “Alternate Units” Tab



Dimension DirectionsDimension Directions Two Basic Forms apply to the Reading

Direction for Dimension Values• Aligned – Dim Values Line Up with Direction of the

Dim’d Feature or Leader

• Unidirectional – All Dims Horizontal– Strongly Preferred due to Ease of Reading



Arcs and AnglesArcs and Angles

“R” Can Lead or Follow (Leading Preferred) Leader Direction Should Run Thru Arc-Center

CoOrd Method (b) More Accurate Use Decimal Degrees (°) over °/’/” (deg/min/sec)



Dim Inside of ObjectDim Inside of Object Whenever Possible Place Dims OUTside the

Object Complex Parts May Require Dims INside



CallOut ShortHand CallOut ShortHand ASME Y14.5M (Geometric Dimensioning And

Tolerancing) Provides Standard Symbols for Common Features• Reduces the Length Of CallOut notes



Dimension Symbol ApplicationDimension Symbol Application

Most Common



Choice of Dimensions The Dimensions You Specify Determine

The Way The Part Is Manufactured And The Way Tolerances Are Applied

Consider the Purpose Of The Part And Its Function In The Assembly

Consider how easy it will be to CHECK the measurement on the actual part

Fully dimension each part

Do not Overdimension, each Dimension should appear ONLY ONCE



Dimension Choice GuidelinesDimension Choice Guidelines Do Not

Overdimension• Redundant Dims

Cause Confusion

Give the DIAMETER of Circular shapes, the RADIUS of Arcs

No redundant or superfluous dimensions

Give SIZE Dimensions for FEATURES.

Give LOCATION dimensions to show how features RELATE to one another.



Contour DimensioningContour Dimensioning

Rectanglular View Center Lines

Dim Where Contour Shape is Most Fully Displayed Do Not Dim to HIDDEN Lines if Possible



Mating Parts → Consistent DimsMating Parts → Consistent Dims

Mating Features should Be Dim’d In the SAME Manner on Both Parts to Ensure Proper Fit



Placement of Dimensions RULES-OF-THUMB for dimension placement

help ensure that others will be able to interpret your drawing

Where placement practices conflict, remember that your goal is to clearly communicate the purpose of the drawing• Use the practice you

feel will make the drawing easier to understand.



Placement Practices Avoid dimensioning

on object. Avoid dimensioning to

hidden lines. Place dimensions

between views when possible.

Group dimensions around a central view

Give OVERALL dimensions where possible.

Place dimensions where the View shows the feature SHAPE.• i.e., Dim to CONTOUR

– i.e., to a CHANGE in DIRECTION

Dimension from or between MACHINED surfaces

Don’t dimension to Rectangular view CENTERLINES.• Dim to Arc/Circle

View Instead



Dimension Prisms (Long Bars)Dimension Prisms (Long Bars) Place Common Dim, Height or Width,

BETWEEN Views



Dimensioning CylindersDimensioning Cylinders Place Common Dim, the Ø, BETWEEN Views The ASME Y14.5 Symbol, Ø, Has Largely

Replaced The Traditional “DIA.” Callout



Dimensioning HolesDimensioning Holes If Possible, Callout to the CONTOUR View If CONCENTRIC Holes (C’Sink or C’Bore)

Leader Points to OUTer Circle



Location DimensionsLocation Dimensions When Locating a Feature Relative to an Edge

• Check with the Fabricator to Determine Which Corner Used As The Origin (Has been Upper Left)

Feature-To-Feature Dimensions Should be Shown in the Contour View Whenever Possible



Baseline DimensioningBaseline Dimensioning

Becoming a De Facto Standard• No Tolerance Build Up

• Matches the X-Y Translation Movement of Modern Machine Tools– Easier CNC Program Development

Ø-Size Specifications



BaseLineBaseLineDim ExampleDim Example

Local Note

Relieves Drawing of Extension-Line “Rat’s Nests”

Generally Eliminates the Need for Dims Inside the Object

“E” Ø Spec



Local NotesLocal Notes Provide Important

Supplementary Information

Characteristics• Brief

• Careful Verbiage



Common (Global) NotesCommon (Global) Notes

Apply to the ENTIRE Drawing Typically Placed in a “Note Block”

• Notes Numbered Sequentially

• Block Located in an “uncrowded” Corner of the Drawing



Dimensioning SummaryDimensioning Summary Good dimensioning is a combination

of choosing dimensions which reflect your DESIGN INTENT, proper technique in creating the details of the dimension line, extension line, arrowheads and dimension values, and placing the dimensions on the drawing so that they can be read clearly.

DIMENSIONING drawings correctly can be as important, or MORE important than drawing the SHAPES correctly.

Good dimensioning requires PRACTICE and THOUGHT



Dimensioning SummarizedDimensioning Summarized

Dimension fully Avoid redundancy Do not dimension to hidden lines Dimension diameter of holes (with Ldr) Dimension radius of arcs Place dimension on view that best

shows feature (Dim to Contour) Group associated dimensions



Dimensioning Super SummaryDimensioning Super Summary

Ask yourself these questions: If I were Making this object or system:• Would I know the SIZE of every Would I know the SIZE of every

Feature (holes, notches, facets, Feature (holes, notches, facets, cutouts, etc.)?cutouts, etc.)?¿?¿?

• Could I LOCATE every Feature Could I LOCATE every Feature relative to a significant OUTSIDE relative to a significant OUTSIDE EDGEEDGE??¿?¿?



All Done for TodayAll Done for Today

MachinedPart

Dimensioning



Bruce Mayer, PELicensed Electrical & Mechanical Engineer

[email protected]

Engineering 25

AppendiAppendixx

6972 23 xxxxf

bruce mayer, pe registered electrical & mechanical engineer bmayer@chabotcollege

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