Chapter 10

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# Chapter 10 - PowerPoint PPT Presentation

Print handouts Select File, Print Edit the following selections to read: Select the OK button. Chapter 10. Tolerancing Printing Instructions:. Tolerancing. Tolerances are used to control the variation in size that exists on all manufactured parts.

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Chapter 10

Tolerancing

Printing Instructions:

Tolerancing
• Tolerances are used to control the variation in size that exists on all manufactured parts.
• The amount that a size is allowed to vary depends on the function of the part & its assembly.
• electric drill vs. jet engine
• The more accuracy required in a part (smaller tolerance) the greater the cost.
• Tolerances allow for interchangeable parts, which permits the replacement of individual parts in an assy. instead of replacing the whole system if a part goes bad or fails.
Tolerance
• Tolerance is the total amount a dimension may vary. It is the difference between the maximum size and the minimum size.
• Tolerances can be expressed on a drawing in several ways:
• direct limits, or as tolerance values applied directly to a dimension. (Fig. 10.8)
• geometric tolerances (Fig. 10.25)
• notes referring to specific conditions
• A general tolerance note in the titleblock. (Fig. 10.7)
Dimensions
• Limit dimensions:
• Plus/minus dimensions:
• unilateral
• bilateral
Tolerancing Terms
• Nominal size: the “name” or general size. Often expressed as a fraction.
• Basic size: the theoretical size used as a starting point for the application of tolerances. Nominal size in decimal format.
• Actual size: the measured size of the finished part.
• Limits: the maximum & minimum sizes shown by the toleranced dimension.
• Allowance: the min. clearance or max. interference between 2 parts.
• MMC: the condition of a part in which it contains the most amount of material.

EX: biggest shaft or smallest hole.

• LMC: the condition of a part in which it contains the least amount of material.
Tolerance, MMC, LMC?
• Limit dimensions:
• Plus/minus dimensions:
• unilateral
• bilateral
Complete Worksheet TOL-1
• Remember x.xxxx
• I.e. 0.1234
• I.e. 2.1200
Fit
• Fit: the degree of tightness between mating parts.
• The three most common types of fit found in industry are:
• Clearance fit - there is always a space between the 2 mating parts. (shaft is smaller than the hole)
• Interference fit - the 2 mating parts always interfere with one another in assembly. (shaft is bigger than the hole)
• Transition fit - sometimes a clearance fit & sometimes an interference fit between the mating parts.
Do on ownpage 335, Figure 10.1a
• Hole Tolerance?
• Shaft Tolerance?
• Minimum clearance?
• Maximum clearance?
• Allowance?
ANSI Standard Fits
• A group of English usit tolerance relationships called preferred precision fits have been developed. They are specified in ANSI B4.1.
• The five classes are:
• Running & sliding fits (RC)
• Clearance locational fits (LC)
• Transition locational fits (LT)
• Interference locational fits (LN)
• Force or shrink fits (FN)
• These tolerances are specified in Appendix 5 through 9, pages a25-a32. The values in these tables are given in THOUSANDTHS of an inch. Example: 1.2 = 0.0012
Class RC9: Running & Clearance FitBasic DIA = 2.0000
• Hole
• Shaft
• Shaft Tolerance =
• Hole Tolerance =
• Max. Clearance =
• Min. Clearance =
Class FN2:Medium Drive fitBasic DIA = 0.5000
• Hole
• Shaft
• Shaft Tolerance =
• Hole Tolerance =
• Max Interference =
• Min Interference =
Metric Fit - Terms
• Basic size: size to which limits of deviation are assigned. (Fig.10.1, p 343)
• Must be same for both parts
• Basic sizes selected from chart in Table 10.2
• Deviation: difference between the actual size and the basic size. (Fig. 10.14)
• Upper deviation: difference between the max. size limit & the basic size.
• Lower deviation: difference between the min. size limit & the basic size.
• Fundamental deviation: the deviation closest to the basic size. (Fig. 10.18)
• Capital H indicates Hole
• Lowercase letter, I.e. f , indicates shaft
Metric Fit – Terms cont’d
• International Tolerance Grade (IT): a group of tolerances that vary depending upon the basic size, but have the same level of accuracy within a given grade. (Fig 10.18)
• There are 18 IT grades. The smaller the grade number, the smaller the tol. zone.
• See Appendix 10 for IT grades.
Preferred Metric Fits
• There are 2 systems used to indicate preferred fits in the metric system.
• Hole basis: the system of fits where the min. hole size is the basic size. The fundamental deviation for a hole basis system is indicated by a capital “H”.
• EX. 50H8

(50 = DIA in mm) (Basic size)

(H = using Basic Hole system) (fundamental deviation)

(8 = closest running fit) (IT grade)

• For mating part 50H8/f7 (Appendix 11)
• Hole Limits?
• Shaft Limits?
• Fit?
Preferred Metric Fits
• The second system used to indicate preferred fits in the metric system.
• Shaft basis: the system of fits where the max. shaft size is the basic size. The fundamental deviation for a shaft basis system is indicated by a lowercase letter.
• EX. 50h7

(50 = DIA in mm) (Basic size)

(h = using Basic Shaft system) (fundamental deviation)

(7 = closest running fit)

• For mating part 50F8/h7 (Appendix ?)
• Limits and Fits?
• Hole Limits?
• Shaft Limits?
• Fit?
Try the following problem
• Basic DIA 41mm
• Use Hole Basis System
• Sliding
Try the following problem
• Basic DIA 41mm
• Use Shaft Basis System
• Sliding
Try the following problem
• Basic DIA 58mm
• Use Shaft Basis System
• Force Fit
Look Up
• What type of fit is a 6 H7/s6?
• Hole or Shaft Basis System?