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Chapter 4 Tolerancing

Chapter 4 Tolerancing. Topics Exercises. Tolerancing: Topics. Summary 4.1) Tolerancing and Interchangeability 4.2) Tolerance Types 4.3) General Definitions 4.4) Tolerancing Standards 4.5) Inch Tolerances 4.6) Metric Tolerances 4.7) Selecting Tolerances

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Chapter 4 Tolerancing

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  1. Chapter 4Tolerancing Topics Exercises

  2. Tolerancing: Topics Summary 4.1) Tolerancing and Interchangeability 4.2) Tolerance Types 4.3) General Definitions 4.4) Tolerancing Standards 4.5) Inch Tolerances 4.6) Metric Tolerances 4.7) Selecting Tolerances 4.8) Tolerance Accumulation 4.9) Formatting Tolerances

  3. Tolerancing: Exercises Exercise 4-1: General definitions Exercise 4-2: Inch tolerance definitions Exercise 4-3: Types of fit Exercise 4-4: Determining fit type Exercise 4-5: Limits and fits Exercise 4-6: Milling jack assembly tolerances Exercise 4-7: Millimeter tolerance definitions Exercise 4-8: Metric fit designation Exercise 4-9: Systems Exercise 4-10: Metric limits and fits

  4. Tolerancing: Exercises Exercise 4-11: Tolerance accumulation Exercise 4-12: Over dimensioning

  5. Tolerancing Summary

  6. Summary • What will we learn in Chapter 4? • We will learn about tolerancing and how important this technique is to mass production. • Key points • If a feature’s size is toleranced, it is allowed to vary within a range of values or limits. • Tolerancing enables an engineer to design interchangeable or replacement parts.

  7. Tolerancing 4.1) Tolerancing for Interchangeability

  8. Tolerancing / Interchangeability • Tolerancing is dimensioning for interchangeability. • What is interchangeability? An interchangeable part is simply a mass produced part (a replacement part).

  9. Tolerancing / Interchangeability • How is a feature on an interchangeable part dimensioned? • The feature is not dimensioned using a single value, but a range of values. 1.005 .994 1.00 →

  10. Tolerancing / Interchangeability • A tolerance is the amount of size variation permitted. • You can choose a tolerance that specifies a large or small variation. 1.005 .994 Size limits = Tolerance = 1.005 - .994 = .011

  11. Tolerancing / Interchangeability • Why do we want a part’s size to be controlled by two limits? It is necessary because it is impossible to manufacture parts without some variation. The stated limits are a form of quality control.

  12. Tolerancing / Interchangeability • Choosing a tolerance for your design. • Specify a tolerance with whatever degree of accuracy that is required for the design to work properly. • Choose a tolerance that is not unnecessarily accurate or excessively inaccurate.

  13. Tolerancing / Interchangeability • Choosing the correct tolerance for a particular application depends on: • the design intent (end use) of the part • cost • how it is manufactured • experience

  14. Tolerancing 4.2) Tolerance Types

  15. Tolerance Types • The tolerancing methods presented are: • Limit dimensions • Plus or minus tolerances • Page or block tolerances

  16. 1. Limit Dimensions • Limits are the maximum and minimum size that a part can obtain and still pass inspection. • For example, the diameter of a shaft might be specified as follows.

  17. 1. Limit Dimension Order • External dimensions: • The larger dimension is first or on top and the smaller dimension is last or on the bottom. • Internal dimensions: • The smaller dimension is first and the larger dimension is last.

  18. Is the following dimension for a shaft or hole? 1. Limit Dimension Order • Why? Does the order matter? • This convention is used to avoid machining mistakes. Shaft

  19. 2. Plus or Minus Tolerances • Plus or minus tolerances give a basic size and the variation that can occur around that basic size.

  20. 3. Page or Block Tolerances • A page tolerance is actually a general note that applies to all dimensions not covered by some other tolerancing type.

  21. Tolerancing 4.3) General Definitions

  22. General Definitions • What are the limits, tolerance and allowance for the following shaft/hole system? Are they the same or different?

  23. General Definitions • Limits:The maximum and minimum diameters. • Tolerance:The difference between two limits. • Allowance:(Minimum Clearance) The difference between the largest shaft diameter and the smallest hole diameter.

  24. Exercise 4-1 General definitions

  25. Exercise 4-1 • What are the limits of the shaft and the hole? • Shaft: • Hole: Dshaft - dshaft dhole - Dhole

  26. Exercise 4-1 • What is the tolerance for the shaft and the hole? • Shaft: • Hole: Dshaft – dshaft = Dhole – dhole =

  27. Exercise 4-1 • What is the minimum clearance (allowance)? dhole – Dshaft =

  28. Exercise 4-1 • What is the maximum clearance? Dhole – dshaft =

  29. Tolerancing 4.4) Tolerancing Standards

  30. Tolerancing Standards • Standards are needed to; • make it possible to manufacture parts at different times and in different places that still assemble properly. • establish dimensional limits for parts that are to be interchangeable.

  31. Tolerancing Standards • The two most common standards agencies are; • American National Standards Institute (ANSI) / (ASME) • International Standards Organization (ISO).

  32. Tolerancing 4.5) Inch Tolerances

  33. Inch Tolerances Definitions • Limits:The limits are the maximum and minimum size that the part is allowed to be. • Basic Size:The basic size is the size from which the limits are calculated. • It is common for both the hole and the shaft and is usually the closest fraction.

  34. Inch Tolerances Definitions • Tolerance:The tolerance is the total amount a specific dimension is permitted to vary.

  35. Exercise 4-2 Inch tolerance definitions

  36. Skip to next part of the exercise Exercise 4-2 • Fill in the following table. .49 - .50 .51 - .47 .5 or 1/2 .04 .01

  37. Inch Tolerances Definitions • Maximum Material Condition (MMC):The MMC is the size of the part when it consists of the most material. • Least Material Condition (LMC):The LMC is the size of the part when it consists of the least material.

  38. Skip to next part of the exercise Exercise 4-2 • Fill in the following table. .49 .51 .50 .47

  39. Inch Tolerances Definitions • Maximum Clearance: The maximum amount of space that can exist between the hole and the shaft. • Max. Clearance = LMChole – LMCshaft

  40. Inch Tolerances Definitions • Minimum Clearance (Allowance): The minimum amount of space that can exist between the hole and the shaft. • Min. Clearance = MMChole – MMCshaft

  41. Exercise 4-2 • Fill in the following table. .50 - .47 = .03 .49 - .51 = -.02

  42. Exercise 4-2 • What does a negative clearance mean? .50 - .47 = .03 .49 - .51 = -.02

  43. Types of Fits • There are four major types of fits. • Clearance Fit • Interference Fit • Transition Fit • Line Fit

  44. Types of Fits • What is a clearance fit? There is always a space. Min. Clearance > 0

  45. Types of Fits • What is an interference fit? There is never a space. Max. Clearance  0

  46. Types of Fits • What is a transition fit? Depending on the sizes of the shaft and hole there could be a space or no space. Max. Clearance > 0 Min. Clearance < 0

  47. Types of Fits • What is a line fit? There is a space or a contact (hole dia = shaft dia) Max. Clearance > 0 Min. Clearance = 0

  48. Exercise 4-3 Types of fits

  49. Exercise 4-3 • From everyday life, list some examples of clearance and interference fits. Lock and Key Door and Door frame Coin and Coin slot Pin in a bicycle chain Hinge pin Wooden peg and hammer toy

  50. Exercise 4-4 Determining fit type

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