Geometric Dimensioning

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Geometric Dimensioning TolerancingReview

• March 10, 2008
• Part 1

2
Design Intent

• Material
• Level of quality
• Relationships
• At the needs stage
• At the functional requirements stage
• At the conceptual design stage

3
Fundamental Philosophy of GDT (Why GDT)

• It is a standard (very similar to ISO)
• It helps communicate design intent
• It could help save money

4
Datum

• A theoretically exact point, axis, or plane
  derived from the true geometric counterpart of a
  specified datum feature. A datum is the origin
  from which the location or geometric
  characteristics of features of a part are
  established.

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Datum Feature

• An actual feature of a part that is used to
  establish a datum

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Datum Feature Simulator

• A surface of adequately precise form (such as a
  surface plate, a gage surface, or a mandrel or a
  CNC machine axis) contacting the datum
  feature(s) and used to establish the simulated
  datum(s).

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Simulated Datum

• A point, axis, or plane established by processing
  or inspection equipment, such as the following
  simulators a surface plate, a gage surface, or a
  mandrel

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Datum Target

• A specified point, line, or area on a part used
  to establish a datum

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From ASME 14.5, 1994.
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From ASME 14.5, 1994.
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From ASME 14.5, 1994.
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From ASME 14.5, 1994.
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Possibilities for
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Possibilities for
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From ASME 14.5, 1994.
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From ASME 14.5, 1994.
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From ASME 14.5, 1994.
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From ASME 14.5, 1994.