GTD

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GTD

• Geometric Tolerances and Dimensions

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Why Geometric Tolerances and Dimensioning

• To ensure interchangeability of mating parts
  during assembly
• To eliminate controversy and guesswork when
  drawing is interpreted
• To ensure the drawing reflects the form and
  function requirements of the manufactured parts

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Principles of datum specification

• Three perfect plans used to locate an imperfect
  part.
• Three point contact is used on the primary plane.
• b. Two point contact is used on the secondary
  plane.
• c. One point contact is used on the tertiary
  plane

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datum specification
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One-Plane Datum Reference Frame
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Two-Plane Datum Reference Frame
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Three-Plane Datum Reference Frame
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Symbols Advantages

• 1. The symbol has uniform meaning.
• 2. Symbols are compact, quickly drawn, and can
  be placed on the drawing where the control
  applies.
• 3. Symbols are the international language and
  surmount individual language barriers.
• 4. Geometric tolerance symbols follow the
  established precedent of other well known symbol
  systems, e.g., electrical and electronic,
  welding, surface texture.

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Using Symbols
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Using Notes
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Symbols/Notes
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Material Condition

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HOLE
PIN
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MMC

• The actual local size of the hole
• at . 245 and the pin at Ø .240
• of the figure are the Maximum material
  condition

Ø
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LMC

• The actual local size of the hole
• at Ø .255 and the pin at Ø .230
• of the figure are the least material condition

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TERMINOLOGY

• VIRTUAL CONDITION - A constant boundary generated
  by the collective effects of a size features
  specified MMC or LMC and the geometric tolerance
  for that material condition.

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VIRTUAL CONDITION

• Virtual condition, based on MMC or L M C
• is a features extreme boundary it represents
  the worse case
• For MMC, worse case concerns fits and/or
  clearances with mating parts For LMC, worst
  case is concerned with strength, alignment, wall
  thickness, etc. with reference to mating parts

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VIRTUAL CONDITION (MMC- PIN)

• Virtual Condition for a Pin
• (Based on Maximum Material Condition)
  Maximum Material Condition the Stated
  Position or Orientation Tolerance
• VC MMC Tolerance

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VIRTUAL CONDITION (MMC- PIN)
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VIRTUAL CONDITION (MMC- Hole)

• Virtual Condition for a Hole
• (Based on Maximum Material Condition)
  Maximum Material Condition - the Stated
  Position or Orientation Tolerance
• VC MMC - Tolerance

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VIRTUAL CONDITION (MMC- Hole)
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VIRTUAL CONDITION (LMC- PIN)

• Virtual Condition for a Pin
• (Based on Least Material Condition)
• Least Material Condition - the Stated Position
  or Orientation Tolerance
• VC LMC - Tolerance

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VIRTUAL CONDITION (LMC- PIN)
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VIRTUAL CONDITION (LMC- Hole)

• Virtual Condition for a Hole
• (Based on Least Material Condition) Least
• Material Condition the Stated Position or
  Orientation Tolerance
• VC LMC Tolerance

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VIRTUAL CONDITION (LMC- Hole)
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