1. Chapter 16
Tolerancing

2. Objectives
Describe the purpose of conventional tolerancing and its limitations
Use standard tables to specify an appropriate fit between two mating parts
Explain the advantages of using geometric dimensioning and tolerancing (GD&T) over conventional tolerancing

3. Objectives (cont’d.)
Recognize the datum reference frame on a drawing with geometric dimensions and tolerances
Describe the tolerance zone shape for each geometric tolerance
Correctly read the feature control frames on a drawing with geometric dimensions and tolerances

4. Introduction Relationships between different parts
Necessary to specify intended fit between parts
Problems with inexperience in new engineers
Lack of knowledge in history, materials
Inappropriate tolerance values

5. Formats for Tolerances
Displayed in several common formats
FIGURE Formats for tolerance dimensioning in millimeters and inches.

6. Tolerance Buildup Problems
Can be minimized depending on type of dimensioning
Chain: yields largest tolerance buildup
Baseline: can eliminate some accumulation
Direct: best way to eliminate tolerance accumulation
Single dimension placed between two key points

7. Statistical Tolerance Control
Based on sound statistical practices
Can be applied only when appropriate statistical process control methods used
FIGURE Tolerancing with statistical process control.

8. Use of Tables for Fits Types of fits
FIGURE Specifying a CLEARANCE FIT with
limit dimensioning.
FIGURE Specifying an INTERFERENCE FIT with limit dimensioning
FIGURE Specifying a TRANSITION FIT with limit dimensioning.

9. Fit Terminology FIGURE 16.11. Clearance fit terminology.
FIGURE Interference fit terminology.

10. English Fits Running or sliding clearance Locational clearance
Locational transition
Locational interference (see next slide)
Force or shrink (see next slide)

11. English Fits (cont’d.)
FIGURE Locational interference and force fits.

12. Metric Fits
FIGURE Metric fit table.

13. Fits Tables
To specify an inch fit between holes and shafts from a standard table
Determine type of fit appropriate for the design and locate corresponding table
Determine basic size of the parts
Find size range on the table
Determine tolerances for hole and shaft
Remember that values on the English tables are in thousandths of an inch

14. Fits Tables (cont’d.)
FIGURE A close sliding fit.

15. Fits Tables (cont’d.) To determine metric fits
Determine type of fit appropriate for the design and locate corresponding table
Determine basic size of the parts
Find the size range on the table
Determine the tolerances for the hole and the shaft

16. Conventional Tolerancing versus Geometric Tolerancing
Feature with size
Cylindrical or spherical surface or set of two opposed elements or opposed parallel surfaces associated with size dimension
Feature without size
Planar surface or a feature where the normal vectors point in the same direction

17. Conventional Tolerancing versus Geometric Tolerancing (cont’d.)
FIGURE Conventional tolerance dimensioning of a block.

18. Conventional Tolerancing versus Geometric Tolerancing (cont’d.)
FIGURE How conventional tolerancing controls surfaces.

19. Location of Holes and Pins with Conventional Tolerancing
FIGURE Square tolerance zones from conventional tolerancing.

20. Geometric Dimensioning and Tolerancing (GD&T)
GD&T is a 3-D mathematical system for describing the form, orientation, and location of features on a part within precise tolerance zones
Better communication throughout design process
Almost nothing can be interpreted in more than one way

21. The Datum Reference Frame
FIGURE Components of the theoretical datum system.

22. The Datum Reference Frame (cont’d.)
FIGURE Datum terminology.

23. Geometry Characteristic Symbols and Feature Control Frames
FIGURE Geometric characteristic symbols.

24. Geometry Characteristic Symbols and Feature Control Frames (cont’d.)
Contains geometric characteristic symbol, the geometric tolerance, and the relative datums
FIGURE A feature
control frame with the
perpendicularity tolerance.
FIGURE A feature control frame with the position tolerance.

25. Order of Precedence for Datums
FIGURE The sequence of datum features

26. Position Tolerances versus Conventional Tolerances
FIGURE Geometric dimensioning and tolerancing of the PLATE.

27. Position Tolerances versus Conventional Tolerances (cont’d.)
Basic dimensions
Theoretically exact
Maximum material condition modifier
Size of zone changes if size of hole changes
Square vs. cylindrical tolerance zones
FIGURE Cylindrical tolerance zones for the position tolerance.

28. Form Tolerances For individual features and not related to datums
Straightness
Flatness
Circularity
Cylindricity

29. Profile Tolerances
FIGURE Profile of a line.

30. Profile Tolerances (cont’d.)
Profile of a surface
Inspection of profile tolerances
Optical comparitors
Overlay charts
Mechanical gaging
Used when datum reference frame applied

31. Orientation Tolerances
Parallelism tolerance
Can be used to control a surface
FIGURE Parallelism tolerance used to control a surface.

32. Orientation Tolerances (cont’d.)
Perpendicularity
Angularity
FIGURE Inspecting the angularity between two surfaces.

33. Location Tolerances Position Can be used to locate axis of a hole
FIGURE Using the position tolerance to locate the axis of a hole.

34. Location Tolerances (cont’d.)
Concentricity
Applied to cylinder
Symmetry
FIGURE Concentricity applied to a cylinder.

35. Runout Tolerances Circular runout Total runout Multiple datums
Tolerances applied based on function, so careful specification of datums is necessary

36. Examples of Specifying Fits and Geometric Tolerances
Specifying the fit between two parts
FIGURE Coupling assembly.

37. Examples of Specifying Fits and Geometric Tolerances (cont’d.)
FIGURE Limit dimensions for the STUD and
BUSHING.

38. Adding Geometric Dimensions
FIGURE PLATE ASSEMBLY.
FIGURE Establishing the datums on the PLATE.

39. FIGURE 16.104. Controlling the datums on the PLATE.

40. FIGURE 16.105. Positioning the hole on the PLATE.

41. FIGURE 16.106. Controlling the other surfaces on the PLATE.

42. Summary
Covered basic information related to conventional tolerancing and GD&T
Discussed interchangeable manufacturing and explained why it is important to the way modern industry functions

43. Summary (cont’d.)
Discussed conventional tolerancing, including how to specify fits and how tolerance dimensions control form and location
Covered the basics of geometric dimensioning and tolerancing

44. Summary (cont’d.)
Discussed the advantages of geometric tolerancing over conventional tolerancing
Explained the importance of the datum reference frame to establish a coordinate system for design manufacturing and inspection
Explained how to read feature control frames
Described each geometric tolerance