15435940 tolerances fits
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tolerances fitsTRANSCRIPT
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Chapter 11
Tolerancing
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TolerancingTolerancing 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 assembly instead of replacing the whole system if a part goes bad or fails.
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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: – a general tolerance note in the
titleblock. – direct limits, or as tolerance values
applied directly to a dimension. (Fig. 11.8)
– geometric tolerances (Fig. 11.31a)– notes referring to specific
conditions (page 364)
ToleranceTolerance
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2.500 ±0.004 0.503 ±0 .003
0.5002.496+0.008-0.000
+0.006-0.000
.500
.506
2.5042.496
Limit dimensions:
Plus/minus dimensions:– unilateral
– bilateral
DimensionsDimensions
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Tolerancing TermsTolerancing 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.
MMC (maximum material condition): the condition of a part in which it contains the most amount of material.
EX: biggest shaft or smallest hole. LMC (least material condition): the
condition of a part in which it contains the least amount of material.
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0.5000.506
2.5042.496
Tolerance, MMC, LMC?Tolerance, MMC, LMC?
Limit dimensions:
Plus/minus dimensions:– unilateral
– bilateral2.500 ±0.004 0.503 ±0 .003
0.5002.496+0.008-0.000
+0.006-0.000
Tolerance? Width Hole
MMC?
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Complete Activity 10 TOL-1
Complete Activity 10 TOL-1
Remember x.xxxx– I.e. 0.1234– I.e. 2.1200
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FitFit 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.
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Tolerancing TermsTolerancing Terms Basic size: the theoretical size
used as a starting point for the application of tolerances.
Nominal size in decimal format. Allowance: the min. clearance or
max. interference between 2 parts.
Clearance
Interference
ClearanceInterference
Minimum
Maximum
Min or Max?
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Clearance FitClearance Fit
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Interference FitInterference Fit
ALLOWANCE =
0.001
0.001
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Page 362 - Hands On 11.1a & b in groups on
the board and c by yourself
Page 362 - Hands On 11.1a & b in groups on
the board and c by yourself
Hands-On (not Figure) 11.1 Are the fits clearance, transitional or interference? Use categories below (Mistakes in textbook)
A B C
Hole Tolerance?
Shaft Tolerance?
Minimum clearance/ interference?
Maximum clearance/ interference?
Allowance?
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Complete Activity 10 TOL-3 #s 4, 5, & 6
Complete Activity 10 TOL-3 #s 4, 5, & 6
Which is between
Largest Hole / Smallest Shaft?
Largest Hole / Largest Shaft?
Smallest Hole / Largest Shaft?
Smallest Hole / Smallest Shaft?
Shaft (Tab)Information given?
Size of tab, clearance fit, allowance0.005, and tolerance on slot is .002.
Minimum or maximum interference?
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Basic SystemsBasic Systems Basic Hole System
– Standard reamers, etc., are used to produce holes and standard gauges used to check sizes. Shafts are machined.
» Determine Minimum hole size, apply allowance, then apply tolerances.
Basic Shaft System – Not used often. However,
advantageous when shafts cannot be easily machined to size or when several parts fit onto one shaft.
» Determine Maximum shaft size, apply allowance, then apply tolerances.
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ANSI Standard FitsANSI Standard Fits A group of English unit tolerance
relationships developed called preferred precision fits. They are specified in ANSI B4.1.
The five classes are: Table 11.1 pg 367– 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 Appendixes 5 through 9, pages a23-a30. The values in these tables are given in THOUSANDTHS of an inch.
Example: 1.2 = 0.0012
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Class RC9: Basic DIA = 2.0000
Class RC9: Basic DIA = 2.0000
Hole limits =
Shaft limits =
Shaft Tolerance = Hole Tolerance = Max. Clearance = Min. Clearance =
RC means?
9 means?
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Class FN2: Basic DIA = 0.5000
Class FN2: Basic DIA = 0.5000
Hole limits =
Shaft limits =
Shaft Tolerance = Hole Tolerance = Max. Interference = Min. Interference =
FN means?
2 means?
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Complete Activity 10 Tol-2 and Finish Tol-3
(#s 1, 2, & 3)
Complete Activity 10 Tol-2 and Finish Tol-3
(#s 1, 2, & 3)
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Metric Fit - TermsMetric Fit - Terms Basic size: size to which limits of deviation are
assigned. (Fig.11.9, p 365)– Must be same for both parts– Basic sizes selected from chart in Table 11.2 (p
371) Deviation: difference between the actual size and the
basic size. (Fig 11.14, p. 369) (Tolerance) Upper deviation: difference between the max. size
limit & the basic size. – Hole system: Upper deviation (tolerance) is the
difference between the largest shaft size and the basic size (minimum clearance or maximum interference, also known as allowance).
– Shaft system: Upper deviation (tolerance) is the difference between the largest hole and the basic size (maximum clearance or minimum interference).
Lower deviation: difference between the min. size limit & the basic size. – Hole system: Lower deviation (tolerance) is the
difference between the smallest shaft size and the basic size (maximum clearance or minimum interference).
– Shaft system: Lower deviation (tolerance) is the difference between the smallest hole and the basic size (minimum clearance or maximum interference, also known as allowance).
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Metric Fit - TermsMetric Fit - Terms
Fundamental deviation: the deviation closest to the basic size. (Fig 11.18, p 370)
Preferred Fits: There are 2 systems used to indicate preferred fits in the metric system. (Table 11.3, page 372)– Hole basis
» Capital H indicates Hole Basis System. – Shaft basis
» Any other capital letter, I.e. S, indicates Shaft Basis System
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Basic Shaft SystemBasic Shaft System
Lower deviation (Maximum clearance)
Upper deviation (Minimum clearance / allowance)
Fundamental deviation for the hole equals the allowance
Basic size applied to shaft – the type of fit will determine whether the basic size will be the largest shaft or the smallest shaft. Fundamental deviation
for the shaft equals the basic size
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Basic Hole SystemBasic Hole System
Basic size applied to hole – the type of fit will determine whether the basic size will be the largest hole or the smallest hole.
Upper deviation (Minimum clearance / allowance)
Fundamental deviation for the shaft equals the allowance
Lower deviation (Maximum clearance)
Fundamental deviation for the hole equals the basic size
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Metric Fit – Terms cont’dMetric 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. (Page 370, Fig 11.17 & 11.16)
– There are 16 IT grades. The smaller the grade number, the smaller the tolerance zone.
– Tolerance Value. See Appendix 10, page a31, for IT grades.
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Preferred Metric FitsPreferred Metric Fits Hole basis: the system of fits where the minimum
hole size is the basic size. The fundamental deviation for a hole basis system is indicated by a capital “H”.
EX. 50H8– Basic size is 50 which is the DIA in mm– Tolerance Grade:
» Hole Symbol: H8» Fundamental deviation is H - capital H
refers to the Basic Hole system» Fundamental deviation value is the
nominal size: » IT grade is 8: Close Running fit
– Tolerance value for 8 is (Append. 10)
– Mating part is f7 (Append. 11-12)
» Shaft Symbol: f7» Fundamental deviation is f
– Fundamental deviation value is the allowance
– Hole Limits? (Append. 11-12)
– Shaft Limits? (Append. 11-12)
– ISO Symbol: = 50H8/f7
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Preferred Metric FitsPreferred Metric Fits 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– Basic size is 50 which is the DIA in mm)– Tolerance Grade:
» Shaft Symbol: h7 » Fundamental deviation is h - lower case
h refers to the Basic Shaft system » Fundamental deviation value is the
nominal size: » IT grade is 7: Close Running fit
– Tolerance value for 7 is (Append. 10)
– Mating part is F8 (Append. 13-14)
» Hole Symbol: F8 – Fundamental deviation value is the
allowance (Append. 13-14)
– Hole Limits? (Append. 13-14)
– Shaft Limits? (Append. 13-14)
– ISO Symbol: 50h7/F8
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Look UpLook Up
What type of fit is a 6H7/s6? (text has a typo – find H7/a6 and fix your text. It should be s instead of a)
– Hole or Shaft Basis System?– Type of Fit?
6S7/h6?– Hole or Shaft Basis System?– Type of Fit?
Shaft Basis System, DIA 32, Locational Interference– Write the specification (ISO Symbol)
for the above information.
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Try the following problem in groups on
the board
Try the following problem in groups on
the board
Given: Basic DIA 41mm, use Hole Basis System, Sliding Fit
Write Specification:
Hole:
Fundamental Deviation =
Fund. Dev. Value =
IT =
IT Value =
Limits =
Tolerance =
Maximum Clearance / Minimum Interference? =
Minimum Clearance / Maximum Interference? =
Allowance =
Shaft:
Fundamental Deviation =
Fund. Dev. Value =
IT =
IT Value =
Limits =
Tolerance =
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Try the following problem in groups on
the board
Try the following problem in groups on
the board
Given: Basic DIA 41mm, use Shaft Basis System, Sliding Fit
Write Specification:
Maximum Clearance / Minimum Interference =
Minimum Clearance / Maximum Interference =
Allowance =
Hole:
Fundamental Deviation =
Fund. Dev. Value =
IT =
IT Value =
Limits =
Tolerance =
Shaft:
Fundamental Deviation =
Fund. Dev. Value =
IT =
IT Value =
Limits =
Tolerance =
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Try the following problem in groups on
the board
Try the following problem in groups on
the board
Given: Basic DIA 58mm, use Shaft Basis System, Force Fit
Write Specification:
Maximum Clearance / Minimum Interference =
Minimum Clearance / Maximum Interference =
Allowance =
Hole:
Fundamental Deviation =
Fund. Dev. Value =
IT =
IT Value =
Limits =
Tolerance =
Shaft:
Fundamental Deviation =
Fund. Dev. Value =
IT =
IT Value =
Limits =
Tolerance =
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Complete Activity 11 Pages Tol-4 & 5
Complete Activity 11 Pages Tol-4 & 5