1. Chapter 15
Dimensioning

2. Objectives Use the concept of dimensioning
Explain the idea of tolerance in dimensioning
Recall the fundamental rules and apply the techniques for dimensioning
Select appropriate dimensions for a moderately complex part and correctly apply them to a drawing of that part

3. Introduction
Dimensioning is much like creating constraint-based solid models
Define the size and location of the features within the software
Part is created “virtually” to your size and location specifications
Develop strategy for determining the types of dimensions required to define apart

4. Is the Dimension I See on a Drawing Exact?
Tolerance: amount of variation
Tolerance dimensions on a detail drawing:
FIGURE The detail drawing of the SHAFT.

5. What Are the Rules for Dimensioning?
National standard: ASME Y14.5M-1994 (ANSI Y14.5)
Published by American Society of Mechanical Engineers
Outlines uniform practices for displaying and interpreting dimensions

6. Millimeters, Inches, or Angstroms?
International System of Units (SI)
Metric
Millimeter is standard unit
U.S. customary units
Decimal inch is standard unit
Both standards are used in United States

7. Types of Dimensioning
Different rules apply to metric- and inch-based drawings
When using millimeters
Show leading zeros for values less than one
Do not show trailing zeros
When using inches
Do not show leading zeros for values less than one
Show trailing zeros equal to precision of drawing

8. Fundamental Rules for Dimensioning
Standards ensure consistency
Examples of fundamental rules
Each dimension shall have a tolerance
Each necessary dimension of an end product shall be shown; show no more dimensions than those necessary for complete definition
The drawing should define a part without specifying manufacturing methods

9. Definitions
FIGURE Dimensioning terminology.

10. Redundancy is Dumb Dimensions should appear only once
Placed according to contour rule
FIGURE Redundant dimensions in (a) are poor practice. Dimensions in (b) are shown once in the view best suited for viewing.

11. Redundancy is Dumb (cont’d.)
Consider fit and function when applying dimensions
FIGURE Dimensions applied, considering the fit and function of the part
named SPACER.

12. Redundancy is Dumb (cont’d.)
Reference dimensions enclosed in parentheses
FIGURE Reference dimensions.

13. Geometrically Correct, but Still Wrong!
When drawings are being used to document parts for manufacture
Accepted rules and practices must be followed to ensure acceptable results

14. Different Ways of Specifying the Same Geometry
Standard ways to specify particular types of geometry
Example: circles dimensioned as diameters and arcs as radii
FIGURE Proper dimensioning of circles and arcs.

15. Identifying and Specifying the Critical Dimensions for Part Function
In the SPACER, most important dimensions are:
Size of machined holes
Distance between the two holes
FIGURE The vise assembly SPACER.

16. FIGURE 15.17. Two possible dimensioned drawings of the SPACER.

17. Baseline versus Chain Dimensioning
FIGURE Baseline dimensioning.
FIGURE Chain dimensioning.

18. What Types of Dimensions Can Be Measured and Checked?
FIGURE Checking the location of an arc center.

19. Guidelines to Guide Your Lines
FIGURE Contour dimensioning.

20. Solid Lines Only Dimension only to visible or solid lines
FIGURE Dimensioning to solid lines.

21. Placement and Spacing
FIGURE Dimension placement and spacing.

22. Font Single-stroke gothic lettering Uppercase
Typical fonts used in CAD software
Century Gothic and Romans.shx

23. Shortcuts Diameters and radii
FIGURE Dimensioning cylinders and holes.
FIGURE Dimensioning arcs.

24. Shortcuts
Chamfers
FIGURE Dimensioning chamfers.

25. Shortcuts (cont’d.)
Standard machined holes: countersinks and counterbores
FIGURE Dimensioning
the sizes of machined holes.
(a) drill (b) blind (c) counterbore (d) countersink (e) spotface

26. Shortcuts (cont’d.) Slots are dimensioned by their diameters
FIGURE Dimensioning slots.

27. Notes General notes apply to entire drawing
Local notes specified with leader line
FIGURE Using local notes.

28. Considerations for 3-D Modeling
Drawings sometimes require more dimensions than models
Geometric relations imbedded in a model must be pointed out explicitly on a drawing
Drawings with dimensions for manufacturing done at end of design process

29. Considerations for 3-D Modeling (cont’d.)
Software points out when drawing underdimensioned or overdimensioned
If underdimensioned, grab entities and move them
If overdimensioned, delete a dimension or geometric constraint

30. Dimensions for the Plate Example
FIGURE A deadbolt lock plate.

31. Dimensions for the Plate Example (cont’d.)
FIGURE Plate dimensions.

32. Fundamental Rules for Dimensioning
Found in ASME Y14.5M-1994 standards for Dimensioning and Tolerancing
Examples
All dimensions and tolerances apply in a free state condition
Unless otherwise specified, all geometric tolerances apply for full depth, length, and width of the feature

33. Summary Provided an introduction to dimensioning
Discussed how all dimensions have a tolerance and how tolerances are important for the function of designs
Discussed specific standards or rules that must be followed whether dimensioning in inches or millimeters

34. Summary (cont’d.)
Covered techniques for dimensioning different features, such as standard parts, machined holes, and notes