2. Dimensioning and Tolerancing Symbology
Chapter 2
Dimensioning and Tolerancing Symbology

3. Objectives
Identify and draw general dimensioning symbols and show their general applications.
Identify and draw tolerancing symbols and show their general applications.
Complete a feature control frame using the correct order of segments in the frame.
Identify basic dimensions and define means for indicating a basic dimension on a drawing or in a design model.

4. General Dimensioning Symbols

5. Features of Size Regular features of size Irregular features of size
Thickness
Width
Length
Diameter
Irregular features of size
Enclosed shape
Collection of features

6. Symbol Application Most symbols precede values
Symbols preferred over abbreviations
Symbol size relative to character height

7. Diameter

8. Spherical Diameter

9. Radius and Controlled Radius

10. Spherical Radius

11. Counterbore and Depth

12. Spotface

13. Countersink

14. Geometric Tolerancing Symbols
Tolerances define allowable variation
Variation occurs in every part
Each tolerancing symbol shape reflects its purpose

15. Reference Value Dimension enclosed in parenthesis
Related symbols are also enclosed

16. Geometric Tolerance Categories
Form
Orientation
Profile
Runout
Location

17. Form

18. Orientation

19. Profile

20. Runout

21. Location Tolerance

22. New Modifiers Least material boundary (LMB)
Maximum material boundary (MMB)
Regardless of material boundary (RMB)

23. Feature Control Frame

24. Feature Control Frame Application
On surfaces
On features of size
On threads

25. Datum Identification Datum feature Datum feature symbol
Datum target symbol
Datum reference frame

26. Datum Feature Symbol Application

27. Datum Target Symbol Used to identify datum target
Identifying letter and number in lower half
Target area size in top half
Movable datum target symbol

28. Datum Targets

29. Basic Dimensions Tolerance shown in feature control frame
Rectangle around dimension
Basic dimensions may be identified by a note

30. ALL DIMENSIONS ARE BASIC or ALL UNTOLERANCED DIMENSIONS ARE BASIC
Basic Dimension Notes
ALL DIMENSIONS ARE BASIC or ALL UNTOLERANCED DIMENSIONS ARE BASIC

31. Past Practices