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Dimensioning

Dimensioning. Chapter 10. Dimensioning. What is the purpose of dimensions? To locate features To specify sizes Geometric shapes ANSI Skill & Practice. Dimensioning. The ability to create good dimensions requires: Technique of dimensioning

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Dimensioning

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  1. Dimensioning Chapter 10

  2. Dimensioning • What is the purpose of dimensions? • To locate features • To specify sizes • Geometric shapes • ANSI • Skill & Practice

  3. Dimensioning • The ability to create good dimensions requires: • Technique of dimensioning • Appearance for lines, spacing, and arrowheads, placement of text • Placement of dimensions • Easy to read, easy to find, logical • Choice of dimensions • Affect how a design is manufactured

  4. Technique of Dimensioning

  5. Technique of Dimensioning

  6. Technique of Dimensioning

  7. Technique in Dimensioning • Arrowheads indicate the extent of dimensions • They should be uniform in size and style throughout the drawing

  8. Technique in Dimensioning

  9. Placing Dimensions

  10. Placing Dimensions

  11. Placing Dimensions

  12. Placing Dimensions

  13. Placing Dimensions

  14. Placing Dimensions

  15. Placing Dimensions

  16. Placing Dimensions • Avoid placing duplicate dimensions AVOID SUPERFULOUS DIMENSIONS

  17. Placing Dimensions

  18. Placing Dimensions - angles • Dimension angles by specifying the angle in degrees and a linear dimension

  19. Placing Dimensions - arcs • A circular arc is dimensioned in the view where you see its true shape by giving the value for its radius preceded by the abbreviation R • Individual fillets and rounds are dimensioned like other arcs • If there are only a few and they are obviously the same size, giving one typical radius is preferred • Fillets radii can also be given in a general note

  20. Placing Dimensions - holes • Show symbols when dimensioning holes • Place leader line in view where hole is shown as a circle • Arrowhead should appear as if it can extend through the center point • Arrowhead should touch the outside of circle

  21. Placing Dimensions - curves • Done by giving group of radii • Dimensioning the outside envelope, with radii • being self-locating

  22. Placing Dimensions - curves • Coordinate method locating points along the curve • Give chordal dimensions as shown below

  23. Placing Dimensions – round shapes • Method used depends on level of accuracy needed • Accuracy may depend on manufacturing method

  24. Dimension Units • Dimension values are lettered horizontally, should read from the bottom of the sheet • Exception – ISO, Architectural dimensions • Engineering drawings – metric or decimal inches • Omit mm and inch designations on drawings and note the units in the title block • Units noted somewhere on the drawing • ALL MEASUREMENTS IN MILLIMTER unless otherwise Noted

  25. Dimension Units • Where the metric dimension is a whole number, do not show a decimal point or a zero (Example 25) • Where the metric dimension is less than 1mm, a zero precedes the decimal point (Example 0.25) • Where the decimal-inch dimension is used, a zero is not used before the decimal point of values less than 1 (Example .25)

  26. Dimension Units - rounding • Preference is to round values to an even number • If the number following the rounding position is less then 5, make no change • If the number following the rounding position is more than 5, round up • If the number following the rounding position is a 5, round to an even number

  27. Dimensioning Units - dual • Dual dimensioning is used to show metric and decimal inch dimensions on the same drawing • Position method • mm placed over inches separated by dim line or they break the dim line and are separated by a slash • Bracket method • mm dimension enclosed • in parentheses

  28. Dimension Units - symbols

  29. Dimension Units - tolerance • When a finished part is measured it may vary slightly from the exact dimension specified • Tolerance is the total amount that the feature on the actual part is allowed to vary from what is specified by the dimension

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