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Copyright 2010 by K. Plantenberg
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Chapter 4
Tolerancing
Topics
Exercises
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Tolerancing: Topics
Summary4.1) Tolerancing and Interchangeability
4.2) Tolerancing Standards
4.3) Tolerance Types4.4) General Definitions
4.5) Inch Tolerances
4.6) Metric Tolerances4.7) Selecting Tolerances
4.8) Tolerance Accumulation
4.9) Formatting Tolerances
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Tolerancing: Exercises
Exercise 4-1: Inch tolerance definitionsExercise 4-2: Types of fit
Exercise 4-3: Determining fit type
Exercise 4-4: Limits and fits
Exercise 4-5: Milling jack assembly tolerances
Exercise 4-6: Millimeter tolerance definitions
Exercise 4-7: Metric fit designation
Exercise 4-8: Systems
Exercise 4-9: Metric limits and fits
Exercise 4-10: Tolerance accumulation
Exercise 4-11: Over dimensioning
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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 features 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
4.1) 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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Tolerancing / Interchangeability
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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Tolerancing / Interchangeability
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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Tolerancing / Interchangeability
Why do we want a parts size to becontrolled 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.
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Tolerancing / Interchangeability
Choosing a tolerance for your design.
Specify a tolerance with whatever degree of
accuracy that is required for the design towork properly.
Choose a tolerance that is not unnecessarily
accurate or excessively inaccurate.
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Tolerancing / Interchangeability
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
4.2) 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
4.3) 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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2. Plus or Minus Tolerances
Plus or minus tolerances give a basicsize and the variation that can occur
around that basic size.
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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
4.4) 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
4.5) 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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Inch Tolerances Definitions
Tolerance: The tolerance is the totalamount a specific dimension is permitted
to vary.
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Exercise 4-2
Inch tolerance definitions
Skip to next part of the exercise
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Exercise 4-2
Fill in thefollowing
table.
Skip to next part of the exercise
Shaft Hole
Limits
Basic Size
Tolerance
.47 - .51 .49 - .50
.5 or 1/2
.04 .01
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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.
Skip to next part of the exercise
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Exercise 4-2
Fill in thefollowing
table.
p p
Shaft Hole
MMC
LMC
.51 .49
.47 .50
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Inch Tolerances Definitions
Maximum Clearance: The maximumamount of space that can exist between
the hole and the shaft.
Max. Clearance = LMCholeLMCshaft
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Inch Tolerances Definitions
Minimum Clearance (Allowance): Theminimum amount of space that can exist
between the hole and the shaft.
Min. Clearance = MMCholeMMCshaft
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Exercise 4-2
Fill in thefollowing
table.
Max. Clearance
Min. Clearance
.50 - .47 = .03
.49 - .51 = -.02
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Exercise 4-2
What doesa negative
clearance
mean?
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 clearance fit?There is always a space.
Min. Clearance > 0
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Types of Fits
What is an in terference fit?There is never a space.
Max. Clearance 0
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Types of Fits
What is a t rans i t ion f i t?Depending on the sizes of the shaft and hole
there could be a space or no space.
Max. Clearance > 0
Min. Clearance < 0
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Types of Fits
What is a l ine fit?There is a space or a contact (hole dia = shaft
dia)
Max. Clearance > 0
Min. Clearance = 0
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Exercise 4-3
Types of fits
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Exercise 4-4
Determining fit type
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Exercise 4-4
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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ANSI Standard Limits and Fits
Locational fits (LC, LT, LN). Locational fits are intended to determine
only the location of the mating parts.
See table 4-3 for a more detailed description.
LC = Locational clearance fits
LT = Locational transition fits
LN = Locational interference fits
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ANSI Standard Limits and Fits
FN: Force Fits. Force fits provide a constant bore pressure
throughout the range of sizes.
See table 4-4 for a more detailed description.
FN1FN5 (tightest)
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Exercise 4-5
Limits and fits
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Exercise 4-5
Given a basic size of .50inches and a fitof RC8, calculate the limits for both the
hole and the shaft.
Use the ANSI limits and fit tables given inAppendix A.
Page A 2
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Page A-2
Basic size = .5
Fit = RC8
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Exercise 4-5
Given a basic size of .50inches and a fitof RC8, calculate the limits for both the
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 4-5
Given a basic size of .50inches and a fitof RC8, calculate the limits for both the
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 4-6
Milling Jack assembly
tolerances
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The V-Anvil fits into the Sliding Screw with a RC4 fit
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The V Anvilfits into the Sliding Screwwith a RC4fit.
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 Screwfits into the
Basewith a RC5fit. The basic
size is .625(5/8). Determine the
limits for both parts.
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Tolerancing
4.6) Metric Tolerances
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Metric Tolerances Definitions
Limi ts, Basic Size,Tolerance, MMC andLMChave the same definition as in the
inch tolerance section.
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Exercise 4-7
Millimeter tolerance definitions
Skip to next part of the exercise
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Exercise 4-7
Fill in thefollowing
table.
Shaft Hole
Limits
Basic Size
Tolerance
2.12.2 1.82.0
2
0.1 0.2
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Metric Tolerances Definitions
Upper deviation: The upper deviation isthe difference between the basic size and
the permitted maximum size of the part.
UD = |basic sizeDmax|
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Metric Tolerances Definitions
Lower deviation: The lower deviation isthe difference between the basic size and
the minimum permitted size of the part.
LD = |basic sizeDmin|
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Metric Tolerances Definitions
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 4-7
Fill in thefollowing
table.
Shaft Hole
UD
LD
FD
0.2 0
0.1 0.2
0.1 0
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Exercise 4-7
Fill in thefollowing
table.
Type of fit Interference
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Metric Tolerances Definitions
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.
Ex: Metric Fit = H11/c11
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Metric Tolerances Definitions
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.
Ex: Metric Fit = H11/c11
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ANSI Standard Limits and Fits
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
A Metric fit is specified by stating thefundamental deviation and the IT#.
Remember!
IT# = the amount that the dimension canvary (tolerance zone size).
Fundamental deviation (letter) = establishes
the position of the tolerance zone with
respect to the basic size. Hole = upper case
Shaft = lower case
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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
Ex: Metric Fit = H11/c11
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Exercise 4-8
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
Metric limits and fits are divided into twodifferent systems; the basic holesystem
and the basic shaftsystem.
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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 4-9
Systems
E i 4 9
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Exercise 4-9
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 4-10
Metric limits and fits
E i 4 10
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Exercise 4-10
Find the limits, tolerance, type of fit, andtype of system for a 30 H11/c11fit.
Use the tolerance tables given in Appendix
A.
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Page A-8
E i 4 10
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Exercise 4-10
Find the limits, tolerance, type of fit, andtype of system for a 30 H11/c11fit.
Shaft Hole
Limits 29.760 - 29.890 30.000 - 30.130
Tolerance
System
Fit
0.13 0.13
Hole
ClearanceLoose Running
Exercise 4 10
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Exercise 4-10
Find the limits, tolerance, type of fit, andtype of system for a 30 P7/h6fit.
Use the tolerance tables given in Appendix
A.
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Page A-11
Exercise 4 10
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Exercise 4-10
Find the limits, tolerance, type of fit, andtype of system for a 30 P7/h6fit.
Shaft Hole
Limits 29.987 - 30.000 29.96529.986
Tolerance
System
Fit
0.013 0.021
Shaft
Locational Interference
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Tolerancing
4.7) Selecting Tolerances
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Selecting Tolerances
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Selecting Tolerances
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
4.8) Tolerance Accumulation
Tolerance Accumulation
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Tolerance Accumulation
The tolerance between two features of apart depends on the number of controlling
dimensions.
Tolerance Accumulation
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Tolerance Accumulation
The distance could be controlled by asingle dimension or multiple dimensions.
Tolerance Accumulation
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Tolerance Accumulation
The maximum variation between twofeatures is equal to the sum of the
tolerances placed on the controlling
dimensions.
Tolerance Accumulation
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Tolerance Accumulation
As the number of controlling dimensionsincreases, the tolerance accumulation
increases.
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Copyright 2010 by K. PlantenbergRestricted use only
Exercise 4-11
Tolerance Accumulation
Exercise 4-11
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Exercise 4-11
What is the tolerance accumulationforthe distance between surface Aand Bfor
the following three dimensioning
methods?
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3070 .
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2070 .
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40.1
109.9
69.8
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1070 .
Exercise 4-11
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Exercise 4 11
If the accuracy of the distance betweensurface A and B is important, which
dimensioning method should be used?
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Exercise 4-12
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 dont match.
Formatting tolerances will be discussed next
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2.983.00
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
4.9) Formatting Tolerances
Formatting Metric Tolerances
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Formatting Metric Tolerances
Tolerances from standardized fit tablesare listed on drawings as;
The person reading the print
has to have access to thestandard fit tables.
Formatting Metric Tolerances
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Formatting Metric Tolerances
Unilateral tolerances
A single zero without a plus or minus sign.
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Formatting Metric Tolerances
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g
Limit dimensions
Both values should have the same numberof decimal places.
Formatting Metric Tolerances
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g
Using Basicdimensions 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.
Formatting Inch Tolerances
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g
Limit dimensions
Both values should have the same numberof decimal places.
Formatting Inch Tolerances
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g
Using Basicdimensions 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