Tolerancing

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Tolerancing

• By
• Dustin
• Carlos
• Eduardo

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Definition

• Tolerance is the total amount a dimension may
  vary and is the difference between the maximum
  and the minimum limits.
• Tolerance is used to control manufacturing
  process more accurately and to control variations
  between mating parts.

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Different ways of Expressing Tolerancing

• Direct limits, applied directly to an object.
• Geometric tolerances.
• Used as notes for specific conditions.
• The last way is general tolerance note in the
  title block.

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General Tolerance

• General Tolerance - is where you put a note about
  tolerancing on the title block so that the
  manufacturer knows how to make the part. If
  there is tolerancing on the part itself the
  manufacturer should ignore the note in the title
  block.

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Types of Tolerance

• Plus/minus dimensioning
• Unilateral tolerance varies in only one
  direction.
• Bilateral tolerance varies in both directions
  from the basic size. Equal in both directions.

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Cost of Tolerance

• Tolerance cost goes up every time that it is
  tightened or changed from a loose fit to a
  tighter fit.
• Tolerance tightening should be avoided if
  possible by other means. The part should be made
  at desired results at the lowest price.
• Changing a tolerance from .10 to .005 can double
  the cost of that feature.

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Terms to Know

• Basic size- The theoretical size used as a
  starting point for applications of tolerances.
• Actual size- the measured size of the finished
  part after machining.
• Limits- the maximum and minimum sizes shown by
  the toleranced dimension.

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Cont.

• Allowance- The minimum clearance or maximum
  interference between parts, or the tightest fit
  between two mating parts.
• Piece Tolerance- The difference between the upper
  and lower limits of a single part.
• System Tolerance- the sum of all the piece
  tolerances.
• Clearance Fit- Space that is always left when
  assembled.

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Cont.

• Interference Fit- happens when assembled he part
  interferes with the mating part.
• Transition Fit- happens when toleranced mating
  parts are either a interference fit or clearance
  fit when assembled.

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Mechanisms

• A mechanical system made of rigid parts or
  structures connected by various linkages, and
  driven by motions or loads.
• Example Gear which is a toothed wheel mechanical
  device used to transmit power and motion between
  machine parts.

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