Lect%2019P.%201

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Functional Dimensioning and Surfaces

• Lecture 19

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Topics For Today

• Quick Review of Dimensioning Principles
• Functional Dimensioning Methods
• Dimensioning to Finished Surfaces

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Principles of Good Dimensioning

• Each feature dimensioned once and only once
• Dimensions should suit the function of the object

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Principles of Good Dimensioning

• Attach dimensions to most descriptive view

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Principles of Good Dimensioning

• Angles as Right Angles Assumed 90o unless
  otherwise noted
• Dimensions outside of object whenever possible

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Principles of Good Dimensioning

• Dimension lines aligned and grouped to promote
  uniform appearance

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Principles of Good Dimensioning

• Dimension lines should be unbroken except for the
  number between the arrowheads
• Space (at least)
• 3/8 in. from object to 1st line
• 1/4 in. from line to next line

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Principles of Good Dimensioning

• Gap object to extension line 1/16 in.
• Extension lines 1/8 in. beyond dimension line
• Extension lines broken for crossing

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Principles of Good Dimensioning

• Leader lines used to dimension circles and arcs
  should be radial

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Principles of Good Dimensioning

• Positive Cylinder in longitudinal view, Holes in
  Circular View, f before value

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Principles of Good Dimensioning

• Internal and external radii should be dimensioned
  with numerical value preceded by the symbol R
  (Note small cross for center.)

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Principles of Good Dimensioning

• Do a final check!
• Every feature has been dimensioned once and only
  once
• Make sure the numerical values are correct

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Dimensioning to Finished Surfaces

• Finished surface (machined, laser cut, etc.) are
  used to get more exact fits.
• Finished surfaces have sharp edges
• Exception If a radius is machined

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Dimensioning to Finished Surfaces

• Finished surfaces should always be used to locate
  features on drawing.

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Locating Features on an Object

• Holes need to be located relative to each other
  or to finished surfaces.

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Dimensioning to Finished Surfaces Assembly
Drawings

• What are the most critical dimensions for the
  function of the assembly?
• How do we dimension to minimize variation in
  critical relationships?
• Examples Today's drawings

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Assignments

• Dwg 37 A24 Dimensioning (metric)
• Select and place the dimensions required to
  complete the detail drawing of the Bracket.
• Keep in mind which dimensions/features are
  important
• Dwg 38 A25-A Dimensions (inches)
• Note that the scale is half size