MEMB113

1. MEMB113 06 Dimensioning

2. Content • Overview • Terminology • Basic Concept • Standard Practice • Detail Dimensioning • Dimensioning Technique • Dimensioning in AutoCAD

3. Overview • Dimension is a way of displaying the size information and feature location on a drawing • Generally consist of lines and number: • dimension lines • extension lines • leader lines • number to indicate the measurement Dimension 20 Dimension line Extension line 4 8 R6

4. Overview • Proper dimensioning should give enough information to manufacture the component • The dimension should not be redundant / over dimension Example of redundant dimensioning

5. Overview • Designs are dimensioned based on two criteria: • Basic sizes and locations of features • Details for construction and for manufacturing • The unit of measurement should be consistent – mm or inches • ALL DIMENSIONS IN MM - should be written on drawing

6. Overview • Generally two types: • Linear dimension: in mm • Angular dimension: in degree, minutes and seconds Linear dimension Angular dimension

7. Example

8. Terminology

9. Basic concept • Size dimension • May be the overall width of a part or the diameter of a hole • Location dimension • May be the length from the edge of an object to the center of a feature Size and location dimensions are used to describe parts for manufacture

10. Basic concept • Basic criteria • “What info necessary to manufacture or construct the object?” • E.g. to drill a hole, need to know • The diameter of the hole • The location of the center • The depth of the hole

11. Basic concept Dimensions showing the location and orientation of features, such as the location of the center of the hole Dimensions showing the size of features, such as the height and depth of the part and the diameter of the hole

12. 20 8 R6 Standard practice • Dimension • the numerical value that defines the size, shape, location, etc. of a feature. • Normally height – 3mm and space between line – 1.5mm 4

13. Standard practice • Dimension line • A thin solid line that shows the extent & direction • Broken for the placing numbers • Placement • Dimension placement depends on the space available • Should follow the standard practices

14. Standard practice EITHER OR

15. Standard practice • Reading direction • All dimensions and note text must be orientated to read from the bottom of the drawing

16. Standard practice • Arrows • Symbols at end of dim. Lines to show limits of the dim. • Uniform in size & style, usually 3mm long & 1/3 as wide • Extension line • A thin solid line perpendicular to dim. line, indicating which feature is associated with dim. • Visible gap • There should be visible gap of 1mm between feature and extension line

17. Standard practice • Leader line - A thin solid line to indicate the feature with which a dimension, note or symbol is associated • Diameter symbol • Radius symbol • Tolerance

18. Standard practice • Spacing • The minimum distance from the object to first dim. is 10mm • Min. spacing between dimensions is 6mm • Should be visible gap between extension line and the feature it refers • Extend beyond dimension lines 2mm Minimum dimension line spacing

19. Standard practice • Grouping and staggering • Dimensions should be grouped for uniform appearance • Do not use object lines as part of your dimensions Group dimensions

20. Standard practice • Extension line • Used to relate a dim. to one or more feature, and usually drawn perpendicular to feature & dim. line • The center of a feature, such as a hole, is located by making the center lines extension lines for the dimension. Extension lines can also cross to mark a theoretical point

21. Standard practice • Extension line should not cross dim lines, are not broken when crossing object or other extension lines, and are broken when crossing arrows

22. Standard practice • View dimensioning • Dimensions should be kept outside the object Dimension outside the view

23. Standard practice • Repetitive feature • The symbol x is used to indicate the number of times a feature is to be repeated Repetitive feature

24. Standard practice • Staggered dimensioning A part dimensioned using coordinate dimensions, with a baseline or datum surface as a starting point

25. Standard practice Stagger dimension text

26. Standard practice • Others • Avoid dimension to hidden lines • The extension line can cross each other, but not dimension line • The extension line can cross the object, but not the dimension line • Avoid dimensioning inside of object • Centre line cannot be used as dimension line, but can be extended as extension line

27. Dimensioning arc/radii Dimensioning arcs Foreshortened leaders

28. Dimensioning circle

29. Dimensioning hole Dimensioning a blind hole

30. Positioning holes

31. Counterbore holes

32. Countersink holes

33. Dimensioning slot, keyway & keyseat Dimensioning keyways & keyseats Dimensioning slots

34. Dimensioning chamfers Dimensioning chamfers

35. Dimensioning sphere & square Dimensioning square Dimensioning small spaces Dimensioning sphere

36. Screw threads

37. Screw threads

38. Screw threads

39. Screw threads

40. Surface finish

41. Representation of common features

42. Representation of common features

43. Dimensioning Technique Geometric breakdown technique

44. Dimensioning symbol

45. Dimensioning symbol

46. Dimensioning symbol

47. MEMB113 Dimensioning with AutoCAD

48. Dimensioning • To add dimension to entity or feature or object. • [pd menu] > Dimension > • [icons …] from ‘Dimension toolbar’ Center Mark Linear Angular Tolerance Aligned Diameter Radius Leader

49. Dimensioning …cont Linear dimension 1st point - [pd menu] > Dimension >Linear - click on 1st point - click on 2nd point - click to place dimension 2nd point 1st point 2nd point Aligned dimension - [pd menu] > Dimension > Aligned - click on 1st point - click on 2nd point - click to place dimension

50. Dimensioning …cont Radius dimension - [pd menu] > Dimension > Radius - click on entity - click to place dimension Circle dimension - [pd menu] > Dimension > Circle - click on entity - click to place dimension