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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

Print handouts

Select File, Print

Edit the following selections to read:

Select the OK button

Chapter 10

Tolerancing

Printing Instructions:

tolerancing
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
  • 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
Dimensions
  • Limit dimensions:
  • Plus/minus dimensions:
    • unilateral
    • bilateral
tolerancing terms
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
Tolerance, MMC, LMC?
  • Limit dimensions:
  • Plus/minus dimensions:
    • unilateral
    • bilateral
complete worksheet tol 1
Complete Worksheet TOL-1
  • Remember x.xxxx
    • I.e. 0.1234
    • I.e. 2.1200
slide8
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 own page 335 figure 10 1a
Do on ownpage 335, Figure 10.1a
  • Hole Tolerance?
  • Shaft Tolerance?
  • Minimum clearance?
  • Maximum clearance?
  • Allowance?
ansi standard fits
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 fit basic dia 2 0000
Class RC9: Running & Clearance FitBasic DIA = 2.0000
  • Hole
  • Shaft
  • Shaft Tolerance =
  • Hole Tolerance =
  • Max. Clearance =
  • Min. Clearance =
class fn2 medium drive fit basic dia 0 5000
Class FN2:Medium Drive fitBasic DIA = 0.5000
  • Hole
  • Shaft
  • Shaft Tolerance =
  • Hole Tolerance =
  • Max Interference =
  • Min Interference =
metric fit terms
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
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
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 fits20
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)

(IT grade)

      • For mating part 50F8/h7 (Appendix ?)
      • Limits and Fits?
        • Hole Limits?
        • Shaft Limits?
        • Fit?
try the following problem
Try the following problem
  • Basic DIA 41mm
  • Use Hole Basis System
  • Sliding
try the following problem22
Try the following problem
  • Basic DIA 41mm
  • Use Shaft Basis System
  • Sliding
try the following problem23
Try the following problem
  • Basic DIA 58mm
  • Use Shaft Basis System
  • Force Fit
look up
Look Up
  • What type of fit is a 6 H7/s6?
  • Hole or Shaft Basis System?