1. Dimensioning
Chapter 10

2. Dimensioning What is the purpose of dimensions? Geometric shapes ANSI
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
Shorter dimension lines are nearest the object outline
Dimension lines should not cross extension lines
A dimension line should never coincide with or extend any line of the drawing
Avoid crossing dimension lines when possible

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