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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 LinesHidden 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

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