Transcript Introduction to Technical Mathematics

05 – Fits and Tolerances
05 – Fits and Tolerances
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The intent of this presentation is to present enough information to provide the reader with a
fundamental knowledge of the different type fits and tolerances used within Michelin and to
better understand basic system and equipment operations.
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05 – Fits and Tolerances
Types of Tolerances and Fits
Introduction to Tolerances and Fits
Definition of Tolerance
A tolerance is the acceptable difference between the maximum and minimum size of a mechanical part as a
basis for determining the accuracy of its fit with another part.
When to use tolerances
Theoretically, each time a dimension is put down on a drawing, a tolerance should be also. In practice, only a
few critical dimensions have particular tolerances and the others are subject to general tolerances.
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05 – Fits and Tolerances
Why tolerance?
Since it is impossible to realize an absolute dimension, it is necessary to determine acceptable limits for this
dimension outside of which the part cannot be used. Since, in industry, a large number of identical parts are
used, it is necessary to be able to interchange these parts and maintain the desired fit without additional
machining. Tolerance also allows us to determine the degree of precision needed in different applications. This
selection of appropriate tolerance avoids unneeded precision of non-precise parts, therefore reducing machining
costs.
How to use tolerances
Tolerances are used by putting the tolerance of each dimension on the drawing and by taking into account the
function of each part, considering the way in which the part is to be manufactured and used.
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05 – Fits and Tolerances
Types of tolerances
The following are the types of size tolerances most often used:
Particular (Special)
This type of tolerance is typically seen on mechanical drawings when specific sizes of a part are needed.
Examples of particular tolerances:
3" +/- 0.003
1.001”
1.0005”
4”
+0.01
−0.00
Particular tolerance is also in the ANSI and ISO tolerance systems. This will be discussed in more detail in the
following pages.
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05 – Fits and Tolerances
General Workshop Tolerance
General workshop tolerances are usually found in the title block of a detail drawing. These tolerances set the
acceptable limits when the fabricator or machinist has no other tolerances given on the drawings.
ANSI (American National Standards Institute)
This type of tolerance system is seen mainly in the United States only. It is associated with the English
measuring system. Examples of ANSI tolerances:
RC1
LC3
FN4
The letters and numbers in these tolerances represent specific tolerances. Further detailed explanations will
follow.
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05 – Fits and Tolerances
I.S.O. (International Standards Organization)
This type of tolerancing system is seen on most all of the European drawings along with many other countries. It
is associated with the metric system. Many U.S. manufacturers are moving towards this type of tolerancing.
Examples of I.S.O. tolerances;
27 H7
40 p6
55 N9
The letters and numbers in these tolerances represent specific tolerances. Further detailed explanations will
follow.
Terminology associated with tolerances
Nominal Dimension - The dimension that the tolerances are applied to.
Upper Limit - The maximum allowable size of the part based on the tolerance
given.
Lower Limit - The minimum allowable size of the part based on the tolerance
given.
Interval of Tolerance - The upper limit minus the lower limit, also known as the range of tolerance.
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05 – Fits and Tolerances
Fits
When assembling two parts together such as a key in a shaft, a bearing on a shaft, a seal into an end-cap, or an
end-cap into a housing, it is termed as the fitting of male and female parts.
The compared size of the male and female parts at the point of contact determines the type of fit the assembly
will form.
A fit is defined as the condition of clearance or interference between two parts
Terminology associated with fits
Allowance - The amount of clearance or interference that exists between two parts.
Maximum Allowance - The greatest amount of clearance or interference that can exist between mating parts.
Equal to the largest female size (upper limit) minus the smallest male size (lower limit).
Minimum Allowance - The least amount of clearance or interference that can exist between mating parts. Equal
to the smallest female size (lower limit) minus the largest male size (upper limit).
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05 – Fits and Tolerances
The three types of fits
Clearance - There will always be some amount of space between mating parts. No force should be required to
put these parts together. When the calculation is performed the allowance values will always be positive.
Interference (Press) - There will always be some amount of contact (interference) between mating parts.
Usually force will be required to put these parts together. Sometimes a great amount of force and sometimes a
firm hand push. When the calculation is performed the allowance values will always be negative.
Uncertain (Transition) - There could exist between mating parts sometimes a condition of clearance or
interference. This would depend on how the parts were tolerated and exactly where within the tolerance range
each part was made. When the calculation is performed the allowance values will be positive and negative.
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05 – Fits and Tolerances
Example 1:
Clearance fit
Note: All dimensions
in inches
Female
Max. dia. = 4.003"
Min. dia. = 4.000"
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Male
Equals
Min. dia. = 3.997"
Max. dia. = 3.999"
(+) 0.006" Pos. clearance
(+) 0.001" Pos. clearance
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05 – Fits and Tolerances
Example 2:
Interference fit
Female
Max. dia. = 6.001"
Min. dia. = 6.000"
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Male
Equals
Min. dia. = 6.002"
Max. dia. = 6.003"
(-) 0.001" Neg. clearance
(-) 0.003" Neg. clearance
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05 – Fits and Tolerances
Example 3:
Uncertain fit
Female
Male
Max. dia. = 8.005"
Min. dia. = 7.998"
Min. dia. = 7.999"
Max. dia. = 8.003"
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Equals
(+) 0.006" Pos. clearance
(-) 0.005" Neg. clearance
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05 – Fits and Tolerances
Systems of Fits
ANSI (American National Standard Institute) and ISO (International Standard Institute) specifications are
systems of fit. The fit specifications are based on application of the part and the tolerances selected to limit the
size of two mating parts to achieve an allowable type of fit.
The type of fit is determined based on the function of the part within the design of the equipment. The fit dictates
the part tolerance(s) and establishes the mating specification needed for two parts to correctly fit together.
Theoretically, an infinite number of fits could be chosen based on the specifications. Standard fits used to cover
most applications are shown in a series of ANSI and ISO tables found in engineering textbooks, machinist
manuals, and quick reference guides for millwrights. The tables that are displayed in this book are condensed
versions provided to give an understanding of the system itself. Full tables have many more nominal size
ranges.
Having knowledge of tolerances will help to understand ANSI and ISO specifications.
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05 – Fits and Tolerances
American National Standards Institute Fits (ANSI)
Designation of Standard Fits
Standard fits are designated by means of the following symbols. The symbols are not intended to be shown on
manufacturing drawings; instead, sizes should be specified on drawings.
The letter symbols used are as follows:





RC Running or Sliding Clearance Fit
LC Locational Clearance Fit
LT Transition Clearance or Interference Fit
LN Locational Interference Fit
FN Force or Shrink Fit
These letter symbols are used in conjunction with numbers representing the class of fit; thus FN4 represents a
Class 4, force fit. With clearance fits, the higher the number-class the greater the clearance between mating
parts. Consequently, with interference fits, the higher the number-class the greater the interference between
mating parts. Each of these symbols, (two letters and a number) represents a complete fit for which the
minimum and maximum clearance or interference and the limits of size for the mating parts are given directly in
the tables.
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Description of Fits
Running and Sliding Fits (RC): Running and sliding fits are intended to provide a similar running performance,
with suitable lubrication allowance, throughout the range of sizes.
Locational Fits (LC, LT, and LN): Locational fits are fits intended to determine only the location of the mating
parts; they may provide rigid or accurate location, as with interference fits, or provide some freedom of location,
as with clearance fits. Accordingly, they are divided into three groups: clearance fits (LC), transition fits (LT),
and interference fits (LN).
Force Fits (FN): Force or shrink fits constitute a special type of interference fit, normally characterized by
maintenance of constant bore pressures throughout the range of size. The interference therefore varies almost
directly with diameter, and the difference between its minimum and maximum value is small, to maintain the
resulting pressures within reasonable limits.
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International Standards Organization (ISO) tolerances and fits
The ISO system of limits and fits for mating parts is approved and adopted for general use in the United States.
It establishes the designation symbols used to define specific dimensional limits on drawings.
The general terms "hole" and "shaft" can also be taken as referring to the space containing or contained by two
parallel faces of any part, such as the width of a slot, or the thickness of a key.
International Tolerance Grades
An "International Tolerance Grade" establishes the magnitude of the tolerance zone or the amount of part size
variation allowed for internal and external dimensions alike. The smaller the grade number the smaller the
tolerance zone.
Grades 1 to 4 are very precise grades intended primarily for gage making and similar precision work, although
grade 4 can also be used for very precise production work.
Grades 5 to 16 represent a progressive series suitable for cutting operations, such as turning, boring, grinding,
milling, and sawing. Grade 5 is the most precise grade, obtainable by the fine grinding and lapping, while 16 is
the coarsest grade for rough sawing and machining.
Grades 12 to 16 are intended for manufacturing operations such as cold heading, pressing, rolling, and other
forming operations.
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05 – Fits and Tolerances
Table 6
IT
GRADES
For Measuring Tools
1
2
3
2
3
4
5
6
For Material
7
8 9 10
For Fits
11
12 13 14 15 16
For Large Tolerances
As a guide to the selection of tolerance grades, on the following page, Table 7 has been prepared to show
grades which may be expected to be held by various manufacturing processes for work in metals. For work in
other materials, such as plastics, it may be necessary to use coarser tolerance grades for the same process.
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Tolerance Position
A fundamental deviation establishes the position of the tolerance zone with respect to the basic size. A tolerance
may be above, below, or astride the nominal dimension. Fundamental deviations are expressed by "tolerance
position letters". Capital letters are used for internal dimensions (bore), and lower case letters for external
dimensions (shaft).
There are 28 possible positions. They are A, B, C, CD, D, E, EF, F, FG, G, H, JS, J, K, M, N, P, R, S, T, U, V, X,
Y, Z, ZA, ZB, ZC; for internal dimensions.
There are also 28 possible positions for external dimensions. They are a, b, c, cd, d, e, ef, f, fg, g, h, js, j, k, m,
n, p, r, s, t, u, v, x, y, z, za, zb, zc.
By combining the IT grade number and the tolerance position letter, the tolerance symbol is established which
identifies the actual maximum and minimum limits of the part. The toleranced sizes are thus defined by the basic
size of the part followed by the symbol composed of a letter and a number.
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05 – Fits and Tolerances
Fits
A fit is indicated by the basic size common to both components, followed by a symbol corresponding to each
component, with the internal part symbol preceding the external part system.
Hole Basis Fits System
In the hole basis fits system, the basic size (nominal dimension) will be the size of the bore. For example, for a
25 H7/f7 fit, which is a preferred hole basis clearance fit, the limits for the hole and shaft will be as follows:
Hole limits = 25.00 - 25.021
Shaft limits = 24.959 - 24.980
Minimum clearance = 0.020
Maximum clearance = 0.062
If a 25 H7/p6 preferred hole basis interference fit is required, the limits for the hole and shaft will be as follows:
Hole limits = 25.00 - 25.021
Shaft limits = 25.022 - 25.035
Minimum interference = (-)0.001
Maximum interference = (-)0.035
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Normally a bore of H7 is
used. The variations in
clearance and
interference which are
necessary in order to
realize the assemblies,
are obtained by the
choice of the shaft
tolerance position.
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Recommended
fits
TYPE OF
FIT
CLEARANCE
TRANSITION
FIT
ASSEMBLY
EXAMPLES OF UTILIZATION
H7/e8
Very easy by
hand
Parts which necessitate high
clearance
H7/f7
Easy by hand
Parts rotating in a bushing
H7/g6
Reasonably
easy
by hand
Sliding parts accurately guided
H7/h6
Possible by
hand
Accurate fixed assembly
H7/k6
Hand or press
When the transmission of little force
is needed
Use a press
When the transmission of a great deal
of force is needed
By expansion
Disassembly impossible without
damaging parts
Outer race by
hand, inner
light press
Follows bearing theory concepts
Outer race
press,
inner by hand
Follows bearing theory concepts
H7/p6
PRESS
H7/s6
ROTATING
SHAFT
H7 HOUSING
k6 SHAFT
ROTATING
HOUSING
N7 HOUSING
g6 SHAFT
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Application and Calculation
Use of Standard Fit Tables
Example 1 - A Class RC1 fit is to be used in assembling a mating hole and shaft of 1.5 inch diameter. This class
of fit was selected because the application required accurate location of the parts with no perceptible play. From
the data in Table 1, establish the limits of size and clearance of the hole and shaft.
Maximum hole = 1.5 + 0.0004 = 1.5004 ; minimum hole = 1.5000 inches
Maximum shaft = 1.5 - 0.0004 = 1.4996 ; minimum shaft = 1.5 - 0.0007 = 1.4993 inches
The resulting clearance possibilities are between 0.0004 and 0.0011 inches.
Tolerance limits given in the tables are added to or subtracted from basic size ( as indicated by + or - sign ) to
obtain maximum and minimum sizes of mating parts.
NOTE: All values shown on an ANSI tolerance chart are in thousandths of an inch.
Example:
+0.2 = 0.0002
+1.2 = 0.0012
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TABLE 1
NOMINAL
SIZE RANGE
IN INCHES
Over - To
To 0Over
- 0.12
To
0.12 - 0.24
0.24 - 0.40
0.40 - 0.71
0.71 - 1.19
1.19 -
1.97
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CLASS
RC1
Hol
e+0.
2
0
+0.
2
0
+0.
25
0
+0.
3
0
+0.
4
0
+0.
4
0
Shaft
-0.1
-0.25
-0.15
-0.3
-0.2
-0.35
-0.25
-0.45
-0.3
-0.55
-0.4
-0.7
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CLASS
RC2
Hole
+0.2
5 0
+0.3
0
+0.4
0
+0.4
0
+0.5
0
+0.6
0
Shaft
-0.1
-0.3
-0.15
-0.35
-0.2
-0.45
-0.25
-0.55
-0.3
-0.7
-0.4
-0.8
CLASS
RC3
Hole
+0.4
0
+0.5
0
+0.6
0
+0.7
0
+0.8
0
+1.0
0
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Shaft
-0.3
-0.55
-0.4
-0.7
-0.5
-0.9
-0.6
-1.0
-0.8
-1.3
-1.0
-1.6
CLASS
RC4
CLASS
RC5
Hole Shaft
+ -0.3
0.6
-0.7
0+ -0.4
0.7
-0.9
0+ -0.5
0.9
-1.1
0+ -0.6
1.0
-1.3
0+ -0.8
1.2
-1.6
0+ -1.0
1.6
-2.0
0
Classification : D3
Classification : D3
Hole
+0.6
0
+0.7
0
+0.9
0
+1.0
0
+1.2
0
+1.6
0
Conservation :
Shaft
-0.6
-1.0
-0.8
-1.3
-1.0
-1.6
-1.2
-1.9
-1.6
-2.4
-2.0
-3.0
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05 – Fits and Tolerances
TABLE 2
NOMINAL
SIZE
RANGE
IN INCHES
- To
Over
To0 - 0.12
Over
To
0.12 - 0.24
0.24 - 0.40
0.40 - 0.71
0.71 - 1.19
1.19 - 1.97
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CLASS
RC6
CLASS
RC7
CLASS
RC8
CLASS
RC9
Hole Shaft Hole Shaft Hole Shaft Hole Shaft
-4.0
-2.5 +2.5
-1.0 +1.6
-0.6 +1.0
+1.0
-5.6
0
-3.5
0
-1.6
0
-1.2
0
-4.5
-2.8 +3.0
-1.2 +1.8
-0.8 +1.2
+1.2
-6.0
0
-4.0
0
-1.9
0
-1.5
0
-5.0
-3.0 +3.5
-1.6 +2.2
-1.0 +1.4
+1.4
-7.2
0
-4.4
0
-2.5
0
-1.9
0
-6.0
-3.5 +4.0
-2.0 +2.8
-1.2 +1.6
+1.6
-8.8
0
-5.1
0
-3.0
0
-2.2
0
-7.0
-4.5 +5.0
-2.5 +3.5
-1.6 +2.0
+2.0
0 -10.5
-6.5
0
-3.7
0
-2.8
0
-8.0
-5.0 +6.0
-3.0 +4.0
\
-2.0
+2.5
0 -12.0
-7.5
0
-4.6
-3.6 +2.5
0
0
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TABLE 3
NOMINAL
SIZE
RANGE
INCHES
Over - To
To
0 - 0.12
Over
To
0.12 - 0.24
0.24 - 0.40
0.40 - 0.71
0.71 - 1.19
1.19 - 1.97
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CLASS LT1
CLASS LT2
CLASS LT3
CLASS LT4
CLASS LT5
Hole
Shaft
Hole
Shaft
Hole
Hole
Shaft
Hole
Shaft
+0.4
0
+0.5
0
+0.6
0
+0.7
0
+0.8
0
+1.0
0
+0.12
- 0.12
+0.15
- 0.15
+0.2
- 0.2
+0.2
- 0.2
+0.25
- 0.25
+0.3
- 0.3
+0.6
0
+0.7
0
+0.9
0
+1.0
0
+1.2
0
+1.6
0
+0.2
- 0.2
+0.25
- 0.25
+0.3
- 0.3
+0.35
- 0.35
+0.4
- 0.4
+0.5
- 0.5
+0.7
+0.1
+0.8
+0.1
+0.9
+0.1
+1.1
+0.1
+0.4
0
+0.5
0
+0.6
0
+0.7
0
+0.8
0
+1.0
0
+0.5
+0.25
+0.6
+0.3
+0.8
+0.4
+0.9
+0.5
+1.1
+0.6
+1.3
+0.7
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+0.6
0
+0.7
0
+0.8
0
+1.0
0
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Shaft
+0.5
+0.1
+0.5
+0.1
+0.6
+0.1
+0.7
+0.1
+0.9
0
+1.0
0
+1.2
0
+1.6
0
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05 – Fits and Tolerances
TABLE 4
NOMINAL
SIZE
RANGE
INCHES
Over - To
To
0 - 0.12
OVER
TO
0.12 - 0.24
0.24 - 0.40
0.40 - 0.71
0.71 - 1.19
1.19 - 1.97
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CLASS LT6
Hole
Shaft
+0.4
0
+0.5
0
+0.6
0
+0.7
0
+0.8
0
+1.0
0
+0.6
5
+0.2
+0.8
5
+0.3
+1.0
+0.4
+1.2
+0.5
+1.4
+0.6
+1.7
+0.7
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TABLE 5
NOMINAL
SIZE
RANGE
INCHES
CLASS FN1
CLASS FN2
CLASS FN3
CLASS FN4
CLASS FN5
Over - To
Hole
Shaft
Hole
Shaft
Hole
Shaft
Hole
Shaft
Hole
Shaft
0
+0.2
0
+0.3
0
+0.4
0
+0.4
0
+0.4
0
+0.5
0
+0.5
0
+0.6
0
+0.6
0
+0.5
+0.3
+0.6
+0.4
+0.7
+0.5
+0.8
+0.5
+0.9
+0.6
+1.1
+0.7
+1.2
+0.8
+1.3
+0.9
+1.4
+1.0
+0.4
0
+0.5
0
+0.6
0
+0.7
0
+0.7
0
+0.8
0
+0.8
0
+1.0
0
+1.0
0
+0.8
+0.6
+1.0
+0.7
+1.4
+1.0
+1.6
+1.2
+1.6
+1.2
+1.9
+1.4
+1.9
+1.4
+2.4
+1.8
+2.4
+1.8
*
*
*
*
*
*
*
*
*
*
*
*
+0.8
0
+1.0
0
+1.0
0
+2.1
+1.6
+2.6
+2.0
+2.8
+2.2
+0.4
0
+0.5
0
+0.6
0
+0.7
0
+0.7
0
+0.8
0
+0.8
0
+1.0
0
+1.0
0
+0.9
+0.7
+1.2
+0.9
+1.6
+1.2
+1.8
+1.4
+1.8
+1.4
+2.1
+1.6
+2.3
+1.8
+3.1
+2.5
+3.4
+2.8
+0.6
0
+0.7
0
+0.9
0
+1.0
0
+1.0
0
+1.2
0
+1.2
0
+1.6
0
+1.6
0
+1.3
+0.9
+1.7
+1.2
+2.0
+1.4
+2.3
+1.6
+2.5
+1.8
+3.0
+2.2
+3.3
+2.5
+4.0
+3.0
+5.0
+4.0
- 0.12
0.12 - 0.24
0.24 - 0.40
0.40 - 0.56
0.56 - 0.71
0.71 - 0.95
0.95 - 1.19
1.19 - 1.58
1.58 - 1.97
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05 – Fits and Tolerances
* Class FN3 for these size ranges does not exist. Applications in this range would use either a FN2 or
FN4.
NOTE: There are only five different classes of fits for force and shrink applications. This normally suffices for
typical applications. For unusual circumstances, a designer would assign specific tolerances to suit the need.
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ISO Tolerance Chart
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05 – Fits and Tolerances
Exercises
1) Find maximum and minimum size for the following tolerances.
a) 30h6
b) 62p6
Answer Key
c) 48H7
d) 105g6
e) 16f7
f) 55N7
g) 4" +/- 0.00038
h) 3.025" +0.005
-0.001
i)
6.00047 +0.00003
-0.00005
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05 – Fits and Tolerances
2) Determine the shaft and hole sizes for the following fits. Also, determine the maximum and minimum
clearances for these fits.
a) 1.2" RC6
Answer Key
b) 0.5" RC2
c) 1.1" LT6
Answer Key
d) 0.75 FN2
e) 35 H7/g6
Answer Key
f) 72 H11/c11
g) 23 H8/f7
Answer Key
h) 55 H7/p6
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05 – Fits and Tolerances
Fit calculation blocks
Example: 10H7/g6
Size
F
10H7
m
10g6
Tol.
+15
0
-5
-14
MAX
MIN


10.015
10.000
9.995
9.986
+0.029
+0.005
IT
0.015
+
0.009
0.024
0.024
-
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05 – Fits and Tolerances
Form and Position Tolerance
Geometric Tolerances Of Form And Position
When?
When the function of a part in a mechanism calls for surfaces whose form and position requires a tolerance.
Why?
Because it is impossible to realize an ideal surface (the theoretical form prescribed by the drawing) which
occupies an ideal position in relation to a reference.
Therefore, for the form and position of this surface, it is necessary to fix acceptable limits beyond which the part
can no longer be used.
How?
By indicating on the functional dimension drawings, the tolerances of form and position, but only if these
tolerances correspond to a functional necessity; this is done in order to avoid overloading and cluttering up the
drawing, which automatically entails needless expenditure.
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05 – Fits and Tolerances
Form and Position Symbols
Form tolerance of an individual element
Line
Straightness
Roundness
Form of any one particular line
Flatness
Cylindricity
Form of any one particular surface
Symbol
Surface
Symbol
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05 – Fits and Tolerances
Form tolerance of associated elements
Association
Parallelism
Squareness
Angularity
Position of the
Element
Concentricity
Symmetry
Symbol
Position Tolerances
Position
Symbol
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05 – Fits and Tolerances
The Drawing Tolerance Block
0.02
Symbol
Tolerance
A
Ref. surface
1. All boxes are drawn in the horizontal position.
2. Arrows go out from 3 sides of the symbol box (centered), as straight lines with as few bends as possible.
3. Boxes are located to give the shortest arrows (leaders) as possible.
4. When the solid reference triangle is used, the reference surface box is omitted.
5. Only one reference triangle can be used with each tolerance.
6. Arrows and the reference triangle will touch the surface, or an extension line from the surface. Do not use
center lines
or dimension lines
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05 – Fits and Tolerances
Definitions:
Upper plane: (of a surface indicated by being flat) Plane which is parallel to the theoretical plane of the surface
in question and which touches the surface without cutting it.
Lower plane: This plane is parallel to the upper plane and is situated at a maximum distance indicated by the
tolerance
Median plane: (of two surfaces indicated as being flat and parallel) This ideal plane is situated midway
between the upper and lower plane and is parallel to both of them.
Whatever the tolerance of form and position or indicated, we shall always apply the same basic principle, be it a
question of a straight line, a cylinder or a circle, depending upon the type of tolerance sought after.
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05 – Fits and Tolerances
Geometric Tolerances
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Surfaces must be concentric within 0.03mm to the reference surface
Surface must be symetrical within 0.05mm to the reference surface A
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Surface must be concentric within 0.1mm to reference surface A
Surfaces must be perpendicular within 0.01mm
Surface must be flat within 0.03mm
Surfaces must be parallel within 0.01mm
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Surface must be perpendicular within 0.1mm to reference surface A
Surface must be concentric within 0.02mm to reference surface
Surface must be parallel within 0.1mm to reference surface A
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05 – Fits and Tolerances
Surface Finish
What is surface finish?
Regardless of how smooth a
surface looks or feels, it
contains some roughness.
Surface finish is a measure of
how smooth or rough a surface
is.
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05 – Fits and Tolerances
Why is surface finish important?
The surface finish will be the determining factor in how well mating parts:
Wear:
 if one slides against the other
 if one turns in the other
Seal:
 mating surfaces must be flat
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05 – Fits and Tolerances
Some examples of these situations would be:
 A shaft turning in a seal
 A cylinder head on a car
 A ball in a ball bearing
 The back and forth action of the ram on the shaper
How is surface finish shown on the drawing?
The surface finish for a part is indicated on the detail drawing of the part. One of the two symbols shown below
will be used to indicate the finish of a surface
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05 – Fits and Tolerances
The numbers in the finish symbol are micro-meters (microns) in the ISO system and micro-inches in the U.S.
system……..…millionth of a meter or inch.
Practical Applications of Surface Finish:
Three important surface finishes to remember are:
1. Bearing seat (housing or shaft)
Ra 1.6 (63 in U.S.)
2. Place on shaft where oil seal rides Ra 0.8 (32 in U.S.)
3. “O” ring in a housing or on a shaft Ra 0.4 (16 in U.S.)
Checking Surface finish:
Surface finish is checked by sight and feel.
This is done by comparing the surface finish on the object we are checking with a surface
having a known roughness value.
The device used for this is a surface finish comparator.
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Ra1.6
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05 – Fits and Tolerances
End of Chapter Five
Exit
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05 – Fits and Tolerances
Return
1) Find maximum and minimum size for the following tolerances.
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Size
Tolerance
Maximum
Minimum
a)
 30 h6
30.0
29.987
b)
 62 p6
62.051
62.032
c)
 48 H7
48.025
48.0
d)
 105 g6
104.988
104.966
e)
 16 f7
15.984
15.966
f)
 55 N7
54.991
54.961
g)
 4”
4.000 38”
3.999 62”
h)
 3.025”
3.03”
3.024”
I)
 6.000 47”
0.00
- 0.013
+ 0.051
+ 0.032
+ 0.025
0.00
- 0.012
- 0.034
- 0.016
- 0.034
- 0.009
- 0.039
+ 0.000 38”
- 0.000 38”
+ 0.005”
- 0.001”
+ 0.000 03”
- 0.000 05”
6.000 5”
6.000 42”
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2) Determine the shaft and hole sizes for the following fits. Also, determine the maximum and minimum
clearances for these fits.
a)
Size
F
M
Tolerance
 1.2” RC6
+ 0.0025”
0.000
- 0.002”
- 0.0036”
 1.2” RC6
Fit = Clearance
Maximum
Minimum
Clear./Inter.
1.2025”
Clear./Inter.
1.2”
Interval of Tol.
(Range)
0.0025”
1.198”
1.1964”
0.0016”
+ 0.0061”
+ 0.002”
0.0041”
0.0041”
Maximum
Minimum
Clear./Inter.
0.5007”
Clear./Inter.
0.5
Interval of Tol.
(Range)
0.0007”
0.5”
0.4996”
0.0004”
+ 0.0011”
0.0”
0.0011”
0.0011”
Return
Size
b)
F
M
Tolerance
 0.5” LC2
+ 0.0007”
0.000
0.000
- 0.004”
 0.5” LC2
Fit = Uncertain
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Size
c)
F
Tolerance
Maximum
Minimum
Clear./Inter.
Clear./Inter.
Interval of Tol.
(Range)
 1.1” LC9
+ 0.005
0.00
1.105”
1.1”
0.005”
 1.1” LC9
- 0.0045”
- 0.008”
1.0955”
1.092”
0.0035”
+ 0.013
+ 0.0045”
0.0085”
0.0085”
M
Fit = Clearance
Return
Size
Tolerance
Maximum
Minimum
Clear./Inter.
Clear./Inter.
Interval of Tol.
(Range)
 0.75” FN2
+ 0.0008”
0.000
0.7508”
0.75”
0.0008”
 0.75” FN2
+ 0.0019”
+ 0.0014”
0.7519”
0.7514”
0.0005”
- 0.0006”
- 0.0019”
0.0013”
0.0013”
d)
F
M
Fit = Interference
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Size
e)
F
M
Tolerance
 35 H7
+ 0.025
0.0
- 0.009
- 0.025
 35 g6
Maximum
Minimum
Clear./Inter.
35.025
Clear./Inter.
35.00
Interval of Tol.
(Range)
0.025
34.991
34.975
0.016
+ 0.05
+ 0.009
0.041
0.041
Fit = Clearance
Return
f)
Size
F
M
Tolerance
 72 H11
+ 0.19
0.0
- 0.15
- 0.34
 72 c11
Maximum
Minimum
Clear./Inter.
72.19
Clear./Inter.
72.0
Interval of Tol.
(Range)
0.19
71.85
71.66
0.19
+ 0.53
+ 0.15
0.38
0.38
Fit = Clearance
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Size
g)
F
M
Tolerance
 23 H8
+ 0.033
0.0
- 0.02
- 0.041
 23 f7
Maximum
Minimum
Clear./Inter.
23.033
Clear./Inter.
23.0
Interval of Tol.
(Range)
0.033
22.98
22.959
0.021
+ 0.074
+ 0.02
0.054
0.054
Fit = Clearance
Return
Size
h)
F
M
Tolerance
 55 H7
+ 0.03
0.0
+ 0.051
+ 0.032
 55 p6
Maximum
Minimum
Clear./Inter.
55.03
Clear./Inter.
55.00
Interval of Tol.
(Range)
0.03
55.051
55.032
0.019
- 0.002
- 0.051
0.049
0.049
Fit = Interference
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