MECH 466

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MECH 466

• Review of Dimensioning

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Dimensioning Review

• Covers all the basics from 161
• Skip the parts you dont need

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Dimensioning Review

• Parts of a dimension
• Basic Shape Dimensioning
• Limit Dimensions
• Functional Dimensioning

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Parts of a Dimension

• Dimension Line
• Arrowheads
• Dimension Number
• Extension Lines
• Leaders

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Parts of a Dimension
Dimension Number
Gap
Extension Line
Leader
Center Line used as Ext. Line
Dimension Line
Arrowhead
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Dimension Line

• line with arrows at each end
• numbers placed near midpoint
• specify size of dimension
• must align parallel to distance measured

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Arrowheads

• at ends of dimension lines and leaders
• mark their endpoints

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Dimension Number

• placed near middle of dimension line
• can be staggered for readability

• gives magnitude of dimension
• omit units of measurement
• also called
• dimension
• dimension text in Solid Edge

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Dimension Numbers

• must be readable from bottom or right side of
  page
• two methods of positioning
• ALIGNED system
• aligns numeral with dimension line
• UNIDIRECTIONAL system
• aligns numeral horizontally
• more widely accepted
• either is acceptable, but dont mix

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Extension Lines

• lines extending from an object for dimensioning
• arrowheads on dimension lines end at these lines
• gap between end of extension line and point on
  object

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Leaders

• arrows drawn from a note to a feature
• note applies to feature
• must touch the referred feature
• near each other
• parallel if possible

Note
Leader

• Donts
• parallel to drawing lines
• through corner
• across each other

Feature
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Basic Shape Dimensioning

• Size dimensions
• Location dimensions
• Practices
• Dos and Donts

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Basic Shape Dimensioning

• enough dimensions to define object completely and
  no more

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Size Dimensioning

• size dimension specifies size of single element
• symbols for
• diameter (DIA, D, phi)

• radius (R)
• fillets rounds (FR)
• anything that looks the same size as a similar
  feature that is dimensioned is the same size if
  undimensioned

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Location Dimensioning

• location dimension indicates position
• 2 geometric elements relative to each other

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Strategy

• break up into simple shapes
• dimension each simple shape (size)
• dimension position of each shape (location)
• check for redundant dimensions
• do in rough form first
• plan for positioning of dimensions on final
  drawing

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Size One Feature
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Size All Features
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Locate One Feature
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Locate All Features
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Practices

• avoid dimensioning to hidden features

• leave 10mm between object and first row/set of
  dimensions

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Redundant Dimension

• watch for redundant dimensions
• see Giesecke Fig. 9.44

Redundant
Redundant
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Redundant Dimension

• always omit least important feature in chained
  dimensions
• tolerances
• all 0.02

0.06
0.02
0.02
0.02
0.02
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Practices

• successive rows of dimensions equally spaced
• overall dimensions at outermost location
• put in last

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DOs and DON'Ts

• Extension lines can cross an object and each
  other
• Nothing can cross a dimension line
• NO EXCEPTION!!!

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DOs and DON'Ts

• use view where shape is most obvious
• use leaders for holes, dimension lines for solid
  cylinders
• diameter for features gt180
• radius if lt180

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DOs and DON'Ts

• never dimension from one edge of a circle to the
  edge of another circle
• except as a reference dimension
• marked REF or in brackets ()
• secondary information
• tolerance consideration doesnt apply
• locate centerlines for cylindrical elements

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DOs and DON'Ts
Reference Dimension
Centers located
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Limit Dimensioning

• Fit
• Single component terms
• 2 component terms
• Clearance Tolerance

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A Fit - 2 Components
Component
Hole
Component
Shaft
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Single Component Terms

• Design Size
• working size during design phase, may be changed
  within a design cycle
• Nominal Size
• approximate size expressed with common fractions
  (1/16") or even digits
• Actual Size
• measured size of finished part

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Single Component Terms

• Basic Size
• exact theoretical size from which limits
  (tolerances) are applied
• Tolerance
• acceptable variations in a dimension
• difference in limit dimension numbers
• Limits of Tolerance
• extreme measurements allowed

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Single Component Terms

• Limit Dimensions
• tolerance in form of largest and smallest
  dimensions
• need not be symmetric about basic size
• Maximum Material Condition (MMC)
• limit dimension with most material is listed
  first
• Note different from text book

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Two Component Terms

• Generic terms
• Hole outermost part
• Shaft innermost part
• Minimum Clearance
• tightest fit between mating parts
• Allowance (Lubrication Theory)
• smallest Hole - largest Shaft

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Two Component Terms

• Maximum Clearance
• loosest fit between mating parts
• largest Hole - smallest Shaft
• Limits of Clearance
• max. and min.
• extremes of clearance allowed

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Clearance Tolerance

• Minimum Clearance (Allowance)
• Smallest Hole - Largest Shaft
• Maximum Clearance
• Largest Hole - Smallest Shaft
• Hole Tolerance
• Largest Hole - Smallest Hole
• Shaft Tolerance
• Largest Shaft - Smallest Shaft

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Clearance Tolerance
Minimum Clearance
Hole Tolerance
Shaft Tolerance
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Functional Dimensioning

• Types
• Planning

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Remarks

• dimensioning as much an art as a science
• requires proper planning and layout
• give just enough specifications to produce parts

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Four Types of Dimensioning

• classify dimensions for planning purposes
• all types are equal but helps organize thinking
• types
• Size Location Dimensioning
• Limit Dimensioning
• Functional Dimensioning
• Manufacturing Dimensioning

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Size Location Dimensioning

• size defines one feature
• length, width, height
• diameter/radius
• location specifies relative position of two
  features

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Limit Dimensioning

• tolerance of size (one part)
• when not covered by general note
• fit (multiple parts)
• limits of clearance
• must be between finished surfaces (see below)
  and/or centerlines
• requires finish marks

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Functional Dimensioning

• relates dimensions to function of component
• size of one or more features
• location of two components by mating features
• dimensions chosen to ensure proper function
• some will be limit dimensions

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Manufacturing Dimensioning

• controls how the part is made
• specifies manufacturing processes applied
• dimensions chosen are those needed for
  manufacturing
• often in the form of notes

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Planning

• start with function
• usually limit dimensions
• fit with mating features
• some limit dimensions
• rest of shape description, manufacturing, etc.
• general tolerance OK

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Cylindrical Features

• dimensioned by diameter
• cylindrical solid sized in rectangular view
• hole sized with leader on circular view
• both located by centerlines
• do NOT dimension fillets, rounds, or run-outs
• provide a shop note

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Manufacturing Dimensioning

• dimension to suit manufacturing methods
• give numbers required by process directly
• machinists are paid to produce parts, NOT to do
  calculations.
• specify machining processes to control tolerances
• eg. DRILL 13.5 (2 PLACES)
• properly sharpened drill has built-in tolerance

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Manufacturing Dimensioning

• finish marks
• V shape

• placed on surfaces when seen as edges
• in EVERY view
• can use extension line for surface if crowded

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Manufacturing Dimensioning

• finish marks
• limit dimensions for accurate location, fit
• eg. hole center relative to machined surfaces
• cosmetic

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Tolerance and Limits

• working drawings use limit dimensions
• Tolerance always finer than the general tolerance
• limits of tolerance need not be equal around
  basic size
• relates to function and manufacturing methods

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General Notes - Examples

• All Fillets Rounds R2 unless otherwise
  specified.
• All Dimensions 0.5mm unless otherwise specified
• All Dimensions in mm

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Final Drawing

• arrange dimensions from planning
• without violating principles, eg.
• never cross dimension lines
• avoid dimensioning hidden features
• locate cylindrical parts by centerlines