SIE1010 Lesson 5.1 - Dimensioning and Tolerancing (Part 1)
Transcript of 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
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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