sie1010 lesson 5.1 - dimensioning and tolerancing (part 1)

8/9/2019 SIE1010 Lesson 5.1 - Dimensioning and Tolerancing (Part 1)

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Lesson Outline

Dimensioning

Units of Measurement

Terminology Associated with Dimensions

Arrangement, Placement and Spacing of Dimensions

Using Dimensions to Specify Size and Location of Features

Dimensioning Rules and Guidelines

Finish Marks

Tolerancing

Definitions

Tolerancing Methods and Tolerance Accumulation

Geometric Tolerances

Tolerancing of Mated Parts

Preferred Metric Limits and Fits


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Dimensioning Introduction

An engineering drawing must include all information needed

to build a part, assembly or system

Technical drawings should include:

Dimensions and general notes describing the size and location of part

features

Details related to the construction or manufacture of the part

A dimension is a numerical value used to define the following

attributes of a part or feature

Size

Location

Geometric characteristic

Surface texture


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Unit of Measurement

Drawings are dimensioned using Metric or English units

Metric system: Millimetres in whole numbers

English/Imperial system: Inches in decimals (typical: 2 dec places)

Add general note: Unless otherwise stated, all dimensions are in

millimetres (or inches)


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Main Goals of Dimensioning

Use only the dimensions needed to completely define a part,

nothing more

Select and arrange dimensions to support the function and

mating relationship of the part

Important: dimensioned part should not be subject to differing

interpretations

In general, do not specify the manufacturing methods to be

used in building the part

Leave options open to manufacturing; avoid potential legal problems

Arrange dimensions for optimum readability

Appear in true profile views, and refer to visible object edges

Unless otherwise stated, assume angles to be 90 degrees


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Terminology

Terminology associated with dimensions


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Direction for Dimensional Values

Unidirectional dimensioning

Values and text are oriented horizontally (for ease of reading)

Aligned dimensioning (older style)

Values are oriented parallel to dimension lines

Not recognized by ANSI


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Arrangement, Placement, Spacing of

Dimensions

Dimensions are arranged for optimum readability

Guidelines to govern spacing, grouping, and staggering of parallel

dimensions

Also guidelines for dimensioning when space is limited

Spacing between parallel dimensions

Grouping and alignment of

parallel dimensions to present a

uniform appearance


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Arrangement, Placement of Dimensions

Staggering of parallel dimensions

to avoid crowdingPossible placement of dimension text;

applies to horizontal, vertical, aligned,

angular and radial dimensions


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Guidelines for Leaders

Multiple leaders in same vicinity

should be parallel;

Leader lines should not be overly long

and cross as few lines as possible

Leaders directed to circle or arc

should pass through circle centre

when extended


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Specify Size and Location of Features

Dimensions are used to specify size and location of features Linear (horizontal, vertical, aligned), radial, diametric, angular

dimensions

Dimensions used to size part features Dimensions used to locate part features


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Symbols, Abbreviations, General Notes

A number of symbols are employed in dimensioning

Common dimensioning symbols General notes and abbreviations used

in dimensioning;

X symbol also used to dimension

multiple features of the same size


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Dimensioning Rules & Guidelines

Occasionally, rules or guidelines may be violated

Due to part complexity, lack of space, conflict with other rules, etc

Rules for prismatic shapes, cylinders and arcs


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Rules & Guidelines for Prisms

Do not repeat dimensions Apply dimensions to a feature in its

most descriptive view

Place dimensions between views

Omit one (intermediate) dimension

Avoid cluttering drawing withunnecessary dimensions

Avoid ambiguity in specifying

tolerances

Include intermediate dimensions that

are easiest to measure with calipers Place smaller dimensions inside of

larger dimensions

Keep drawing organized, avoid

extension lines that cross dimension

lines

Rules and guidelines for

dimensioning prisms


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Rules & Guidelines for Prisms

Dimension to visible object lines, notto hidden lines

Keep dimensions outside of views

If drawing view is cluttered or leader line

needs to be extremely long, then this

rule may be overriden

Extension lines may cross object lines

and other extension lines

In general, desirable to avoid lines that

cross

But permissible for an extension line to

cross an object line or another extensionline

More rules and guidelines

for dimensioning prisms


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Rules & Guidelines for Cylinders & Arcs

Dimension diameter of cylindrical

parts in their rectangular view

Dimension diameter of cylindrical

holes in their circular view

Dimension radius of circular arcs inthe view where their true shape is

seen

For arcs 180 degrees, specify diameter

Note use of symbols: R, , Places, TYP

Avoid overly long extension and

leader lines

Rules and guidelines for

dimensioning cylinders and arcs


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Assembly of Mating Parts

An assembly is made up of two or more mating parts


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Complex Assembly of Parts

John Deere Tractor Assembly Drawing


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Surface Finishing

Parts produced by casting have rough external surfaces When cast parts are used in an assembly

Surfaces in contact with other parts are machined or finished to

provide smooth mating surfaces, reduce friction, etc


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Casting Process

Casting is a manufacturing process by which a liquid material

is usually poured into a mold, which contains a hollow cavity

of the desired shape, and then allowed to solidify. The

solidified part is also known as a casting, which is ejected or

broken out of the mold to complete theprocess.

Sand Casting Process

http://www.youtube.com/watch?v=szOwGvYO_Tc

Investment Casting Process

http://www.youtube.com/watch?v=BX8w-GUPz1w

http://www.youtube.com/watch?v=tyrXq_u1OH0
http://www.youtube.com/watch?v=szOwGvYO_Tchttp://www.youtube.com/watch?v=szOwGvYO_Tchttp://www.youtube.com/watch?v=szOwGvYO_Tchttp://www.youtube.com/watch?v=BX8w-GUPz1whttp://www.youtube.com/watch?v=BX8w-GUPz1whttp://www.youtube.com/watch?v=BX8w-GUPz1whttp://www.youtube.com/watch?v=tyrXq_u1OH0http://www.youtube.com/watch?v=tyrXq_u1OH0http://www.youtube.com/watch?v=tyrXq_u1OH0http://www.youtube.com/watch?v=tyrXq_u1OH0http://www.youtube.com/watch?v=BX8w-GUPz1whttp://www.youtube.com/watch?v=szOwGvYO_Tc


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Finish Marks

A finish mark symbol () is used to indicate that a surface is to be

machined

Finish marks are applied to all edge views (visible or hidden) of finished

part surfaces


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Surface Texture Symbols

Surface texture symbols and construction

Application of surface symbols to a part


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Surface Finish in Manufacturing

Surface roughness produced by various manufacturing methods


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Surface Finish in Manufacturing

Surface roughness produced by various manufacturing methods

sie1010 lesson 5.1 - dimensioning and tolerancing (part 1)

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