Dimensioning%20and%20Tolerancing

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Dimensioning and Tolerancing

• David Quigley
• February 7, 2006

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Dimensioning

• Definition
• A dimension is a numerical value expressed in
  appropriate units of measure and indicated on a
  drawing
• A dimensioned drawing should provide all the
  information necessary for a finished product or
  part to be manufactured.

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Dimensioning Example

• An example dimension is shown below.

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Rules for Dimensioning

• Use one type of dimensioning consistently
• General units can be omitted if stated somewhere
  on the drawing
• Projection lines do not touch the object and are
  drawn perpendicular to the element you are
  dimensioning.
• All dimensions less than 1 should have a leading
  zero. i.e. .35 should be written as 0.35

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Types of Lines

• Thin chain lines indicate center lines.
• Dashed lines are for hidden lines.

Center Lines
Hidden Lines
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Types of Dimensioning

• Parallel Dimensioning
• Has several dimensions starting from one
  projection line.

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Types of Dimensioning

• Chain Dimensioning
• Having the dimensioning start after each previous
  dimension
• Chains of dimension should only be used if the
  function of the object won't be affected by the
  accumulation of the tolerances.

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Types of Dimensioning

• Combined Dimensioning
• This type combines Chain and Parallel Dimensioning

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Types of Dimensioning

• Dimensioning Holes
• Holes can be dimensioned with coordinates

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Dimensioning Holes
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Stagger Dimension Values
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How to dimension small objects

• When dimensioning small features, placing the
  dimension arrow between projection lines may
  create a drawing which is difficult to read. So,
  use one of the below techniques.

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Dimensioning Circles

• All dimensions of circles are proceeded by this
  symbol .
• There are three different ways to dimension
  circles

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Circle Dimensioning

• (a) two common methods
• (b) Used when the circle is too small
• (c) outside dimensioning

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Tolerancing

• Definition
• The total allowable variation an acceptable part
  can have from the specified dimension.
• The less variation allowed, the more the part
  will cost to make

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Complicated Example
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Tolerancing Rules

• Each dimension on a drawing must include a
  tolerance value.
• a general tolerance value applicable to several
  dimensions. i.e. a note specifying that the
  General Tolerance /- 0.5 mm.
• or a tolerance specific to that dimension

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Tolerancing Example

• The upper limit for the tolerance goes on top of
  the lower limit.

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Dimensioning Exercises

• Complete the Handout Exercise

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Questions/Comments
?