1. Dimensioning & Tolerancing Dr. Fairuz I. Romli Semester 2 2009/2010

2. Introduction: Dimensioning Working drawings must show dimensions and contain notes conveying sizes, specifications and other information Techniques of dimensioning presented are based primarily on the standards of the American National Standards Institute (ANSI) Two commonly used units of measurement Metric units – in millimeter – round the millimeters to the nearest whole number English units – in inches – always show up to two decimal places, even for whole numbers Earle, J. H. “Graphics for Engineers”, Addison-Wesley Publishing, 1996

3. Dual Dimensioning On some drawings, both metric and English units might be required Place the millimeter equivalent either under or over the inch units Place the converted dimension in brackets to the right of the original dimension Be consistent in the arrangement throughout the whole drawing Earle, J. H. “Graphics for Engineers”, Addison-Wesley Publishing, 1996

4. Metric Designation In metric system (SI) First-angle projection positions the front view over the top view and the right-side view to the left of the front view American system – use third-angle projection – places top view over the front view Label metric drawings with one of the symbols Earle, J. H. “Graphics for Engineers”, Addison-Wesley Publishing, 1996

5. Numeric & Symbolic Dimensioning Vertical dimensions – aligned or uni-directional Uni-directional – all dimensions appear in the standard horizontal position Aligned – numerals are parallel with vertical and angular dimension lines and read from the right-hand side of the drawing, never from the left-hand side Earle, J. H. “Graphics for Engineers”, Addison-Wesley Publishing, 1996

6. Numeric & Symbolic Dimensioning Placement Dimensions should be placed on the most descriptive views of the part being dimensioned First row of dimensions should be at least 3 times the letter height (3H) from the object Successive rows of dimensions should be spaced equally at least 2 times the letter height (2H) Regardless of space limitations – numerals have to be the same size throughout the entire drawing Earle, J. H. “Graphics for Engineers”, Addison-Wesley Publishing, 1996

7. Numeric & Symbolic Dimensioning Earle, J. H. “Graphics for Engineers”, Addison-Wesley Publishing, 1996

8. Numeric & Symbolic Dimensioning Symbols To save some drawing times – use these symbols instead of words Size usually based on the letter height – often 1/8 inch Earle, J. H. “Graphics for Engineers”, Addison-Wesley Publishing, 1996

9. Dimensioning Rules To place dimensions and notes on drawings most effectively However, from time to time, rules of dimensioning must be violated due to the complexity of the part or shortage of space Rules for prisms Place the first row of dimensions at least 3H from the object Successive rows at least 2H from each other Earle, J. H. “Graphics for Engineers”, Addison-Wesley Publishing, 1996

10. Dimensioning Rules Rules for prisms Place the dimensions between the views sharing these dimensions Earle, J. H. “Graphics for Engineers”, Addison-Wesley Publishing, 1996

11. Dimensioning Rules Rules for prisms Place the dimensions on the most descriptive views of an object Earle, J. H. “Graphics for Engineers”, Addison-Wesley Publishing, 1996

12. Dimensioning Rules Rules for prisms Dimension visible features, not hidden features Earle, J. H. “Graphics for Engineers”, Addison-Wesley Publishing, 1996

13. Dimensioning Rules Rules for prisms Leave the last dimension blank in a chain of dimensions when you also give an overall dimension Earle, J. H. “Graphics for Engineers”, Addison-Wesley Publishing, 1996

14. Dimensioning Rules Rules for prisms Place dimensions in well-organized lines for uncluttered drawings Earle, J. H. “Graphics for Engineers”, Addison-Wesley Publishing, 1996

15. Dimensioning Rules Rules for prisms Do not duplicate dimensions on a drawing to avoid errors or confusion Earle, J. H. “Graphics for Engineers”, Addison-Wesley Publishing, 1996

16. Dimensioning Rules Rules for prisms Dimension lines should cross any other lines unless absolutely necessary Earle, J. H. “Graphics for Engineers”, Addison-Wesley Publishing, 1996

17. Dimensioning Rules Rules for prisms Extension lines may cross other extension lines or object if necessary Earle, J. H. “Graphics for Engineers”, Addison-Wesley Publishing, 1996

18. Dimensioning Rules Rules for prisms Leave a small gap from the edges of an object to extension lines that extend from them. Do not leave gaps where extension lines cross object lines or other extension lines Earle, J. H. “Graphics for Engineers”, Addison-Wesley Publishing, 1996

19. Dimensioning Rules Rules for prisms Earle, J. H. “Graphics for Engineers”, Addison-Wesley Publishing, 1996

20. Dimensioning Rules Rules for angles Place angular dimensions outside angular notches by using extension lines Earle, J. H. “Graphics for Engineers”, Addison-Wesley Publishing, 1996

21. Dimensioning Rules Rules for angles Dimension a bent surface rounded corner by locating its theoretical point of intersection with extension lines Earle, J. H. “Graphics for Engineers”, Addison-Wesley Publishing, 1996

22. Dimensioning Rules Rules for cylindrical parts and Holes Dimension the diameter (not the radius) of a cylinder in the rectangular view Earle, J. H. “Graphics for Engineers”, Addison-Wesley Publishing, 1996

23. Dimensioning Rules Rules for cylindrical parts and Holes Dimensions on concentric cylinders are easier to read if they are staggered within their dimension lines Earle, J. H. “Graphics for Engineers”, Addison-Wesley Publishing, 1996

24. Dimensioning Rules Rules for cylindrical parts and Holes Dimension holes in their circular view with leaders whenever possible, but dimension them in their rectangular views if necessary Earle, J. H. “Graphics for Engineers”, Addison-Wesley Publishing, 1996

25. Dimensioning Rules Rules for cylindrical parts and Holes Draw leaders pointing toward the centers of holes Earle, J. H. “Graphics for Engineers”, Addison-Wesley Publishing, 1996

26. Dimensioning Rules Rule for leaders Extend leaders from the first or the last word of a note with a horizontal elbow Earle, J. H. “Graphics for Engineers”, Addison-Wesley Publishing, 1996

27. Dimensioning Rules Rule for arcs and radii When space permits, place dimensions and arrows between the center and the arc When space is not available for the numbers, place the arrow between the center and the arc number outside If there is no space for the arrow inside, place both the dimension and arrow outside the arc with a leader Earle, J. H. “Graphics for Engineers”, Addison-Wesley Publishing, 1996

28. Dimensioning Rules Rule for location dimensions Locate cylindrical holes in their circular views by coordinates to their centers Earle, J. H. “Graphics for Engineers”, Addison-Wesley Publishing, 1996

29. Introduction: Tolerancing Technique of dimensioning parts within a required range of variation Each dimension is allowed a certain degree of variation within a specified zone A tolerance should be as large as possible without interfering with the function of the part to minimize production costs Manufacturing costs increase as tolerances become smaller Positioning of tolerances Earle, J. H. “Graphics for Engineers”, Addison-Wesley Publishing, 1996

30. Rules of Tolerancing Order of numbers Place upper limits either above or to the right of lower limits In plus minus tolerancing, place the plus limits above the minus limits Earle, J. H. “Graphics for Engineers”, Addison-Wesley Publishing, 1996

31. Rules of Tolerancing Positioning of numbers Spacing and ratios of numerals used to specify tolerances on dimensions Earle, J. H. “Graphics for Engineers”, Addison-Wesley Publishing, 1996

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