Tolerancing - Chapter 8

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Copyright ©2009 by K. Plantenberg

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Chapter 8

Tolerancing

Topics

Exercises


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Tolerancing: Topics

Summary 8.1) Tolerancing and Interchangeability

8.2) Tolerancing Standards

8.3) Tolerance Types 8.4) General Definitions

8.5) Inch Tolerances

8.6) Metric Tolerances 8.7) Selecting Tolerances

8.8) Tolerance Accumulation

8.9) Formatting Tolerances


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Tolerancing: Exercises

Exercise 8-1: Inch tolerance definitions Exercise 8-2: Types of fit

Exercise 8-3: Determining fit type

Exercise 8-4: Limits and fits

Exercise 8-5: Milling jack assembly tolerances

Exercise 8-6: Millimeter tolerance definitions

Exercise 8-7: Metric fit designation

Exercise 8-8: Systems

Exercise 8-9: Metric limits and fits

Exercise 8-10: Tolerance accumulation

Exercise 8-11: Over dimensioning


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Tolerancing

Summary


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Summary

What will we learn in Chapter 8?→ 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 allowedto vary within a range of values or limits.

→ Tolerancing enables an engineer to design

interchangeable or replacement parts.


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Tolerancing

8.1) Tolerancing for

Interchangeability


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Tolerancing / Interchangeability

Tolerancing is dimensioning forinterchangeability.

What is interchangeability?

An interchangeable part is simply a mass

produced part (a replacement part).



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How is a feature on an interchangeablepart dimensioned?

→ The feature is not dimensioned using asingle value, but a range of values.

1.00 →

1.005

.994



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A tolerance is the amount of sizevariation permitted.

→ You can choose a tolerance that specifies a

large or small variation.

1.005

.994

Tolerance = 1.005 - .994 = .011

Size limits =


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Choosing the correct tolerance for aparticular application depends on:

→ the design intent (end use) of the part→ cost

→ how it is manufactured

→ experience


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Tolerancing

8.2) Tolerancing Standards


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Tolerancing Standards

Standards are needed to;

→ make it possible to manufacture parts at

different times and in different places thatstill assemble properly.

→ establish dimensional limits for parts that

are to be interchangeable.


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Tolerancing Standards

The two most common standardsagencies are;

→ American National Standards Institute(ANSI) / (ASME)

→ International Standards Organization (ISO).


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Tolerancing

8.3) Tolerance Types


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Tolerance Types

The tolerancing methods presentedare:

→ Limit dimensions

→ Plus or minus tolerances→ Page or block tolerances


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1. Limit Dimensions

Limits are the maximum and minimumsize that a part can obtain and still

pass inspection.

→ For example, the diameter of a shaft might

be specified as follows.


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1. Limit Dimension Order

The high limit is placed above the lowlimit. When both limits are placed on one

line, the low limit precedes the high limit.


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3. Page or Block Tolerances

A page tolerance is actually a generalnote that applies to all dimensions not

covered by some other tolerancing

type.


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Tolerancing

8.4) Shaft-Hole Assembly


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Shaft-Hole Assembly

Used to illustrate concepts and definitions.Both the shaft and the hole are allowed to

vary between a maximum and minimum

diameter.


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Tolerancing

8.5) Inch Tolerances


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Inch Tolerances Definitions

Limits: The limits are the maximum andminimum 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 shaftand is usually the closest fraction.


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Tolerance: The tolerance is the totalamount a specific dimension is permitted

to vary.


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Exercise 8-2

Inch tolerance definitions

Skip to next part of the exercise


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Exercise 8-2

Fill in thefollowing

table.


Shaft Hole

Limits

Basic Size

Tolerance

.47 - .51 .49 - .50

.5 or 1/2

.04 .01


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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.



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Exercise 8-2


table.

p p

Shaft Hole

MMC

LMC

.51 .49

.47 .50


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Maximum Clearance: The maximumamount of space that can exist between

the hole and the shaft.

→ Max. Clearance = LMChole – LMCshaft


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Exercise 8-2


table.

Max. Clearance

Min. Clearance

.50 - .47 = .03

.49 - .51 = -.02


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Types of Fits

There are four major types of fits.→ Clearance Fit

→ Interference Fit

→ Transition Fit→ Line Fit


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Types of Fits

What is a l ine fi t ?There is a space or a contact (hole dia = shaft

dia)

Max. Clearance > 0

Min. Clearance = 0


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Exercise 8-3

Types of fits


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Exercise 8-3

From everyday life, list some examples ofclearance and interference fits.

Fit Example

Clearance

Interference

Lock and Key

Door and Door frame

Coin and Coin slot

Pin in a bicycle chain

Hinge pin

Wooden peg and hammer toy


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Exercise 8-4

Determining fit type


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Exercise 8-4

Determine the basic size and type of fitgiven the limits for the shaft and hole.

Shaft Limits Hole Limits Basic

Size

Type of fit

1.498 - 1.500 1.503 - 1.505

.751 - .755 .747 - .750

.373 - .378 .371 - .375

.247 - .250 .250 - .255

1.5 Clearance

.75 Interference

.375 Transition

.25 Line


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ANSI Standard Limits and Fits

The following fit types and classes are inaccordance with the ANSI B4.1-1967

(R1994) standard.


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RC: Running or Sliding Clearance fit.→ Intended to provide running performance

with suitable lubrication.

• See table 8-2 for a more detailed description.

→ RC9 (loosest) – RC1 (tightest)


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Locational fits (LC, LT, LN).→ Locational fits are intended to determine

only the location of the mating parts.


• LC = Locational clearance fits

• LT = Locational transition fits

• LN = Locational interference fits


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FN: Force Fits.→ Force fits provide a constant bore pressure

throughout the range of sizes.


→ FN1 – FN5 (tightest)


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Exercise 8-5

Limits and fits


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Exercise 8-5

Given a basic size of .50 inches and a fitof RC8, calculate the limits for both the

hole and the shaft.

→ Use the ANSI limits and fit tables given in Appendix A.


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Exercise 8-5


hole and the shaft.

→ Standard Limits Hole = +2.8 0

→ Standard Limits Shaft = -3.5 -5.1

These are the values that we add/subtract

from the basic size to obtain the limits.

What are the units?

See page A-1.


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Exercise 8-5


hole and the shaft.

→ Hole Limts = .50 - 0 = .5000

.50 + .0028 = .5028

→ Shaft Limits = .50 - .0035 = .4965

.50 - .0051 = .4949


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Exercise 8-6

Milling Jack assembly

tolerances


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Exercise 8-6

Consider the MillingJack assembly

shown.

→ Notice that there aremany parts that fit

into or around other

parts.

→ Each of these partsis toleranced to

ensure proper fit and

function.


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The V-Anvil fits into the Sliding Screw with a RC4 fit


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The V Anvil fits into the Sliding Screw with a RC4 fit.

The basic size is .375 (3/8). What are the limits?

.3750 - .3759

.3739 - .3745

The Sliding Screw fits into the


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The Sliding Screw fits into the

Base with a RC5 fit. The basic

size is .625 (5/8). Determine the

limits for both parts.

The Sliding Screw fits into the Base with a RC5 fit


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The Sliding Screw fits into the Base with a RC5 fit.

The basic size is .625 (5/8). What are the limits?

.6231 - .6238

.625 - .626


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Tolerancing

8.6) Metric Tolerances


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Metric Tolerances Definitions

Limi ts , Basic Size, Tolerance, MMC andLMC have the same definition as in the

inch tolerance section.


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Exercise 8-7

Millimeter tolerance definitions



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Exercise 8-7


table.

Shaft Hole

Limits

Basic Size

Tolerance

2.1 – 2.2 1.8 – 2.0

2

0.1 0.2


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Upper deviation: The upper deviation isthe difference between the basic size and

the permitted maximum size of the part.

→ UD = |basic size – Dmax|


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Lower deviation: The lower deviation isthe difference between the basic size and

the minimum permitted size of the part.

→ LD = |basic size – Dmin|


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Fundamental deviation: Thefundamental deviation is the closest

deviation to the basic size.

→ The fundamental deviation is the smaller ofthe UD and the LD.

→ A letter in the fit specification represents the

fundamental deviation.

Ex: Metric Fit = H11/c11


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Exercise 8-7


table.

Shaft Hole

UD

LD

FD

0.2 0

0.1 0.2

0.1 0


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Exercise 8-7


table.

Type of fit Interference


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International tolerance grade number(IT#): The IT#’s are a set of tolerances

that vary according to the basic size and

provide the same relative level of

accuracy within a given grade.

→ The number in the fit specification

represents the IT#.

→ A smaller number provides a smallertolerance.



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Tolerance zone: The fundamentaldeviation in combination with the IT#

defines the tolerance zone.

→ The IT# establishes the magnitude of thetolerance zone or the amount that the

dimension can vary.

→ The fundamental deviation establishes the

position of the tolerance zone with respectto the basic size.



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The following fit types are in accordancewith the ANSI B4.2-1978 (R1994)

standard.


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Available Metric Fits

Hole Basis Shaft Basis FitH11/c11 C11/h11 Loose running

H9/d9 D9/h9 Free running

H8/f7 F8/h7 Close running

H7/g6 G7/h6 Sliding

H7/h6 H7/h6 Locational clearance

H7/k6 or

H7/n6

K7/h6 or

N7/h6

Locational transition

H7/p6 P7/h6 Locational interference

H7/s6 S7/h6 Medium drive

H7/u6 U7/h6 Force

The difference between Hole

and Shaft Basis Fits will be

discussed in an upcoming

section.


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Tolerance Designation

Fits are specified by using the:→fundamental deviation (letter)

→IT# (International Tolerance Grade #).

When specifying the fit:→The hole = upper case letter

→The shaft = lower case letter



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Exercise 8-8

Metric fit designation

Fill in the appropriate name for the fit component.


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Fill in the appropriate name for the fit component.

Basic size

Fundamental Deviation IT#

Hole Tolerance Zone

Shaft Tolerance Zone


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Basic Hole / Basic Shaft Systems

Basic hole system: The basic holesystem is used when you want the basic

size to be attached to the hole dimension.

→ For example, if you want to tolerance a shaft

based on a hole produced by a standard

drill, reamer, broach, or another standard

tool.


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Basic Hole / Basic Shaft Systems

Basic shaft system: The basic shaftsystem is used when you want the basic

size to be attached to the shaft dimension.

→ For example, if you want to tolerance a hole

based on the size of a purchased a

standard drill rod.


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Exercise 8-9

Systems

E i 8 9


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Exercise 8-9

Identify the type of fit and the system usedto determine the limits of the following

shaft and hole pairs

Shaft Hole Type of Fit System

9.972 - 9.987 10.000 - 10.022

60.002 - 60.021 60.000 - 60.030

39.984 - 40.000 39.924 - 39.949

Clearance Hole

Transition Hole

Interference Shaft


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Exercise 8-10

Metric limits and fits

E i 8 10


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Exercise 8-10

Find the limits, tolerance, type of fit, andtype of system for a n30 H11/c11 fit.

→ Use the tolerance tables given in Appendix

A.


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E i 8 10


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Copyright ©2009 by K. PlantenbergRestricted use only

Exercise 8-10

Find the limits, tolerance, type of fit, andtype of system for a n30 H11/c11 fit.

Shaft Hole

Limits 29.760 - 29.890 30.000 - 30.130

Tolerance

System

Fit

0.13 0.13

Hole

Clearance – Loose Running

Exercise 8 10


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Exercise 8-10

Find the limits, tolerance, type of fit, andtype of system for a n30 P7/h6 fit.

→ Use the tolerance tables given in Appendix

A.


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Page A-11

Exercise 8 10


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Exercise 8-10

Find the limits, tolerance, type of fit, andtype of system for a n30 P7/h6 fit.

Shaft Hole

Limits 29.987 - 30.000 29.965 – 29.986

Tolerance

System

Fit

0.013 0.021

Shaft

Locational Interference


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Tolerancing

8.7) Selecting Tolerances

Selecting Tolerances


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Tolerances will govern the method ofmanufacturing.

→ When the tolerances are reduced, the cost

of manufacturing rises very rapidly.

→ Specify as generous a tolerance as

possible without interfering with the

function of the part.



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Choosing the most appropriate tolerancedepends on many factors such as;

→ length of engagement,

→ bearing load,

→ speed,→ lubrication,

→ temperature,

→ humidity,→ and material.

Experience also plays a significant role.

Machining and IT Grades


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Machining and IT Grades


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Tolerancing

8.8) Tolerance Accumulation


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Tolerance Accumulation


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The maximum variation between twofeatures is equal to the sum of the

tolerances placed on the controlling

dimensions.



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As the number of controlling dimensionsincreases, the tolerance accumulation

increases.



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Remember, even if the dimension doesnot have a stated tolerance, it has an

implied tolerance.


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Exercise 8-11


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Exercise 8-11

What is the tolerance accumulation forthe distance between surface A and B for

the following three dimensioning

methods?


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2070 .


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40.1

109.9

69.8


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1070 .

Exercise 8-11


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Exercise 8 11

If the accuracy of the distance betweensurface A and B is important, which

dimensioning method should be used?


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Exercise 8-12

Over dimensioning

Assuming that the diameter dimensions are correct,

explain why this object is dimensioned incorrectly


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explain why this object is dimensioned incorrectly.

1. The decimal places don’t match.

Formatting tolerances will be discussed next


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2.98 – 3.00

Formatting tolerances will be discussed next.

2. The dimensions are inconsistent.

1.98 + .99 = 2.972.01+1.00 = 3.01

This part is over dimensioned.


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Tolerancing

8.9) Formatting Tolerances

Formatting Metric Tolerances


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Tolerances from standardized fit tablesare listed on drawings as;

The person reading the print

has to have access to thestandard fit tables.



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Unilateral tolerances

→ A single zero without a plus or minus sign.



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Bilateral tolerances

→ Both the plus and minus values have thesame number of decimal places.



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g

Limit dimensions

→ Both values should have the same numberof decimal places.



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g

Using Basic dimensions with the tolerance

→ The number of decimal places in the basicdimension does not have to match the

number of decimal places in the tolerance.

Formatting Inch Tolerances


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g

Unilateral and Bilateral tolerances

→ The basic dimension and the plus and

minus values should have the same number

of decimal places.



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g

Limit dimensions

→ Both values should have the same numberof decimal places.



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g

Using Basic dimensions with the tolerance

→ The number of decimal places in the basicdimension should match the number of

decimal places in the tolerance.

Formatting Angular Tolerances


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g g

Angular tolerances

→ Both the angle and the plus and minusvalues have the same number of decimal

places.


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Tolerancing

The End

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Tolerancing - Chapter 8