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Dimensioning and Tolerancing

Dimensioning and Tolerancing. David Quigley February 7, 2006. Dimensioning. Definition: A dimension is a numerical value expressed in appropriate units of measure and indicated on a drawing

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Dimensioning and Tolerancing

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  1. Dimensioning and Tolerancing David Quigley February 7, 2006

  2. 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.

  3. Dimensioning Example • An example dimension is shown below.

  4. 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

  5. Types of Lines • Thin chain lines indicate center lines. • Dashed lines are for hidden lines. Center Lines Hidden Lines

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

  7. 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.

  8. Types of Dimensioning • Combined Dimensioning • This type combines Chain and Parallel Dimensioning

  9. Types of Dimensioning • Dimensioning Holes • Holes can be dimensioned with coordinates

  10. Dimensioning Holes

  11. Stagger Dimension Values

  12. 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.

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

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

  15. 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

  16. Complicated Example

  17. 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

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

  19. Dimensioning Exercises • Complete the Handout Exercise

  20. Questions/Comments ?

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