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Feature Control Frame

GD&T

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The Feature Control Frame

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The Geometric Characteristic Symbol

Always the first symbol in the frame.

Only one per frame.

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Geometric Characteristic Symbols

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Tolerance Value (& zone descriptor)

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Full Indicator Movement (FIM)

The tolerance given is always a total value (like FIM), it is NOT plus or minus.

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Using a Dial Test Indicator

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Tolerance Zone

If the zone is identified as a diameter, the zone is a cylinder.

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If there is no zone descriptor, it is parallel to the surface or a uniform boundary in the shape of the desired form.

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Tolerance Zone Modifiers

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Datum

The datums referenced in the feature control frame are identified on the drawing with a "plunger" symbol.

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Datum Identifier

Parts are imperfect, surface plates are better, but are still datum simulators.

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Precedence of Datums

  1. First A
  2. Then B
  3. Then C

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...but does it make a difference? (Hint: YES)