tolerancing - chapter 8
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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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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
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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Inch Tolerances Definitions
Tolerance: The tolerance is the totalamount a specific dimension is permitted
to vary.
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Exercise 8-2
Inch tolerance definitions
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Exercise 8-2
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 8-2
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 = LMChole – LMCshaft
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Exercise 8-2
Fill in thefollowing
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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ANSI Standard Limits and Fits
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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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 8-3 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 8-4 for a more detailed description.
→ 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
Given a basic size of .50 inches 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 8-5
Given a basic size of .50 inches 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 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
Fill in thefollowing
table.
Shaft Hole
Limits
Basic Size
Tolerance
2.1 – 2.2 1.8 – 2.0
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 size – Dmax|
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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 size – Dmin|
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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 8-7
Fill in thefollowing
table.
Shaft Hole
UD
LD
FD
0.2 0
0.1 0.2
0.1 0
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Exercise 8-7
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
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 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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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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Selecting Tolerances
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.
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
8.8) Tolerance Accumulation
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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.
Tolerance Accumulation
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Tolerance Accumulation
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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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.
Formatting Metric Tolerances
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Formatting Metric Tolerances
Bilateral tolerances
→ Both the plus and minus values have thesame number of decimal places.
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 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.
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 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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