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Chapter 11
Datums

Excerpt

Readers will learn:

1. To select the optimal datum features for parts.

2. The rules for defining datum features, applying geometric tolerances to datum features and the most appropriate material condition symbols.

3. The six spatial degrees of freedom and how to assign datum features to stabilize a part.

4. How to fixture a part properly on its datum features.

5. How to designate the degrees of spatial freedom eliminated by each datum feature on a part.

6. How to apply angular orientation datum features and what affect they have on part stability.

7. How to establish a valid datum plane for rocking or wobbling datum features per ASME Y14.5.1-Mathematical Definition of Dimensioning and Tolerancing Principles

8. The effects of differing datum precedence on part acceptance.

9. How to define and fixture a curved surface as a datum feature.

10. How to define a conical surface as a datum feature and what it means.

11. How to define and fixture a pattern of holes as a datum pattern at MMB and RMB.

12. How to establish 3 mutually perpendicular datum planes from 3 surfaces that are not mutually perpendicular.

13. How to utilize complex and constant cross-section datum features.

14. How to specify degrees of freedom in the feature control frame.

15. How to identify multiple datum reference frames.

16. How to specify the desired datum material boundary with a number.

17. How to calculate the correct MMB and LMB.

18. How to use the translation modifier.

19. How to utilize the term ‘basic’ or its abbreviation in a feature control frame.

20. The meaning of planar datum features referenced at RMB and MMB.

21. How to specify and interpret irregular datum features of size at RMB and MMB.

22. How to specify and interpret repetitive patterns.

  • -How They are Selected and What They Mean
  • -Specifying Degrees of Freedom
  • -Datum Feature Simulation
  • -Designating Degrees of Freedom on the Part Drawing
  • -Establishing a Valid Datum Plane
  • -Effects of Differing Datum Precedence on Part Acceptance
  • -Curved Surface as a Datum Feature
  • -Conical Datum Features
  • -Datum Feature Pattern Referenced Regardless of Material Boundary
  • -Inclined Datum Feature
  • -Constant Cross-Sections and Complex Datum Features
  • -Specifying Degrees of Freedom in the Feature Control Frame
  • -Multiple Datum Reference Frame Identification
  • -Correct Material Boundary Size Specified Next to the Datum Feature
  • -Correct Material Boundary Calculations
  • -Using the Translation Modifier
  • -Basic or BSC Spelled Out in a Feature Control Frame
  • -Planar Datum Feature Simulated at Regardless of Material Boundary (RMB)
  • -Planar Datum Feature Simulated at Maximum Material Boundary (MMB)
  • -Offset Datum Features of Size Simulated at RMB and MMB
  • -Profiled Datum Features Simulated at RMB and MMB
  • -Irregular Datum Features of Size

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