58235646-limits 29116s
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INTRODUCTION TO LIMITS, FITS, INTRODUCTION TO LIMITS FITS TOLERANCE AND GD&T TOLERANCE AND GD&T 03‐02‐08
PURPOSE OF MASS PRODUCTION PURPOSE OF MASS PRODUCTION (Interchangeability) I mass production, In d ti b interchangeability, by i t h bilit identical components manufactured by diff different t personnell under d diff different t environment, can be assembled and replaced without ith t any further f th rectification tifi ti d i during th the assembly stage, without affecting the f ti i functioning off the th componentt when h assembled
NECESSITY OF THE LIMIT SYSTEM If components are to be interchangeable, they need to be manufactured to the same size which is not possible, when they are mass produced. It becomes b necessary to t the th operator t to t deviate d i t by a small margin from the exact size (BASIC SIZE). SIZE) At the same time,, the deviated size should not affect the quality of the assembly. This sort of dimensioningg is known as limit dimensioningg
A system of limits A system of limits is to be followed as a standard is to be followed as a standard for the for the limit dimensioning of components Various system of limits and fits are followed by different Various system of limits and fits are followed by different countries based on the ISO specifications. The system of limits and fits followed in our country is that Th t f li it d fit f ll di t i th t stipulated by the BIS(BUREAU OF INDIAN STANDARDS) OTHER SYSTEM OF LIMITS AND FITS INTERNATIONAL STANDARDS ORGANISATION (ISO) BRITISH STANDARD SYSTEM (BSS) GERMAN STANDAD (DIN) ( )
TERMINOLOGY‐ THE INDIAN STANDARD SYSTEM OF LIMITS & FITS Size: It is a number expressed in a particular unit in the measurement of length Basic Size: It is the size based on which the dimensional deviations are given. Actual Size: It is the size of the component by actual measurement after it is manufactured. It should lie between the two limits of size if f d h ld l b h l f f the component is to be accepted
Limits of size: These are the extreme permissible sizes within which the operator is expected to make the component. Maximum limit of size: It is the greater of the two limit of sizes. Minimum limit of size: It is the smaller of the two limits of sizes. Hole: In the BIS system of limits & fits, componentt including i l di those th which hi h are nott as “Hole” Shaft: In the BIS system of limits & fits, component including those which are not as shaft.
all internal features of a cylindrical li d i l are designated d i t d
all external features of a cylindrical are designated
HOLE
SHAFT
Deviation: It is the algebraic difference between a limits of size to its corresponding basic size. It may be positive, negative or zero. Upper deviation: pp It is the algebraic difference between the maximum limit of size to its corresponding basic size maximum limit of size to its corresponding basic size. Lower deviation: It is the algebraic difference between the minimum limit of size to its corresponding basic size.
Actual deviation It is the algebraic difference between the actual size and its corresponding basic size. p g Tolerance: It is the difference between the maximum limit of size and minimum limits of size. It is always positive and is expressed only as a number without a sign is expressed only as a number without a sign. Zero line: In graphical representation of above , the zero line represents the basic size. This line is also called as the line of zero deviation.
• Is there any two things identical ?
• Why Variations? Wh V i ti ?
NO
Men M hi Machine Material
SHAFT BASIC DIAMETER 20MM
20mm
SHAFT DIAMETER : MAY GO UP TO 20.3 mm
20.3 mm
SHAFT SPECIFICATION
+ 0.30 - 0.00
20
?
SHAFT SPECIFICATION
+ 0.30 - 0.00
20
TOLERANCE
Dimensions and Tolerance communicate in the size and shape of the part. A Dimension A Di i is a numerical value expressed in i i l l di appropriate units of measure and used to define Size, location orientation form or other geometric location, orientation, form or other geometric characteristics of the part.
A Tolerance is the total amount that part features are permitted to vary from their specified dimensions. It is the difference between the maximum and minimum limit i i li i
SOLVE THE PROBLEM
ON THE DRAWING WHICH LETTER INDICATES A LIMIT TOLERANCE? ON THE DRAWING,WHICH LETTER INDICATES A LIMIT TOLERANCE?
ON THE DRAWING, WHICH LETTER INDICATES A PLUS OR MINUS TOLERANCE?
Fundamental Deviation: Th There are 28 fundamental f d t l deviations d i ti i the in th BIS system t represented by letter symbols The fundamental deviations are for achieving the different classes of fits
Schematic representation of the positions of fundamental deviations
Fundamental tolerance: This is also called ‘grade of tolerance’. In the Indian g Standard System , there are 18 grades of tolerances
A high number gives a _____________ tolerance zone.
LARGE A high number gives a _____________ tolerance zone.
Toleranced size: This includes the basic size, the fundamental deviation and the grade of tolerance.
25H7( toleranced size of a ___________)
HOLE
25H7( toleranced size of a ___________)
30h7 ( toleranced size of a _____)
Shaft 30h7 ( toleranced size of a _____)
Calculate the tolerance for a. 25H7 b. 30h7 b. 30h7
NO.
SIZE OF THE COMPONENT
UPPER DEVIATION
LOWER DEVIATION
MAX. LIMIT OF SIZE
MIN, LIMIT OF SIZE
Exercise : : Exercise 120 G7 20 g6
NO.
SIZE OF THE COMPONENT
UPPER DEVIATION
LOWER DEVIATION
MAX. LIMIT OF SIZE
MIN, LIMIT OF SIZE
FITS
Fit: It is the relationship that exists between two mating parts, a hole and a shaft., with respect to their dimensional diff difference between assembly b bl Expression of a fit: Example 30 H7/g6 (or) 30 H7‐g6 (or) 30
H7 g6
TYPES
1 Cl 1. Clearance Fit Fit
Clearance: In a fit the clearance is the difference between the size of the hole and the size of the shaft which is the size of the hole and the size of the shaft which is always positive. Clearance fit: It is a fit which always provides clearance. Here the tolerance zone of the hole will be above the tolerance zone of the shaft.
Clearance: In a fit the clearance is the difference between the size of the hole and the size of the shaft which is the size of the hole and the size of the shaft which is always positive. Clearance fit: It is a fit which always provides clearance. Here the tolerance zone of the hole will be above the tolerance zone of the shaft.
The limits of the hole are 20 + 0.021 = 20.021 mm 20 + 0 = 20.000 mm For a shaft 20 g6 we find in the table ‐7 ‐20 20 So the limits of the shaft are 20 ‐ 0.007 = 19.993 mm 20 ‐ 0.020 = 19.980 mm
Maximum clearance: In a clearance fit or transition fit, it is the difference In a clearance fit or transition fit it is the difference between the maximum hole and minimum shaft Minimum clearance: In a clearance fit, it is the difference between the minimum hole and maximum shaft
The minimum clearance is The minimum clearance 20.000 – 19.993 = 0.007 mm Th The maximum clearance i l i is 20.021 – 19.980 = 0.041 mm
There is always a clearance between the hole and the shaft. This is the Clearance fit.
2 I t f 2. Interference Fit Fit
Interpret the following 25H7/p6
Interference: It is the difference between the size of the hole and the shaft before assembly, and this is negative. In this case, the shaft is always larger than the hole size. Interference fit: It is a fit which always provides interference. Here the y p tolerance zone of the hole will be below the tolerance zone of the shaft.
Maximum Interference: Maximum Interference: In an interference fit or transition fit, it is the algebraic difference between the minimum hole and the maximum shaft. Minimum Interference: In an interference fit, it is the algebraic difference In an interference fit it is the algebraic difference between the maximum hole and the minimum shaft The maximum interference is The maximum interference 25.035 – 25.000 = 0.035 mm Th The minimum interference i i i t f i is 25.022 – 25.021 = 0.001 mm
3 T 3. Transition Fit iti Fit
Interpret the following 75 H8/j7 75 H8/j7
Transition fit: Transition fit: It is a fit which may sometimes provide clearance, and sometimes interference. When this class of fit is represented graphically the tolerance zones of the hole and shaft will overlap each other. Example; The limits of the hole are 75.046 mm (Max.limit of size) 75.000 mm (Min.limit of size) The limits of the shaft are 75.018 mm (Max.limit of size) ( ) 74.988 mm (Min.limit of size)
Max. clearance = Max. limit of hole – Max clearance = Max limit of hole Min. limit of shaft Min limit of shaft = 75.046 ‐74.988 = 0.058mm Max. interference = Max. limit of shaft – Min. limit of hole = 75.018 – 75.000 = 0.018 mm
This is a transition fit because it can result in a clearance fit or an This is a transition fit because it can result in a clearance fit or an interference fit.
BASIC SHAFT SYSTEM FIT
SHAFT HOLE
CLEARANCE
h
A up to H
TRANSITION
h
J up to N
INTERFERENCE
h
P up to ZC
BASIC HOLE SYSTEM FIT
HOLE
SHAFT
CLEARANCE
H
a up to h
TRANSITION
H
j up to n
INTERFERENCE
H
p up to zc
T Types of System fS t
In the BASIC HOLE system, the basic part is the hole, while the shaft is the mating part shaft is the mating part. In the BASIC SHAFT system, the basic part is the shaft, while the hole is the mating part. o e s t e at g pa t
Group Exercises
Determine Determine the type of fit
Determine Determine the type of fit
Determine the type of fit f fi
Identify the types of fits 30H7 / g6 / 30H7 / p6 30H7 / p6 30H7 / m6 30H7 / m6
PURPOSE OF MASS PRODUCTION PURPOSE OF MASS PRODUCTION (Interchangeability) I mass production, In d ti b interchangeability, by i t h bilit identical components manufactured by diff different t personnell under d diff different t environment, can be assembled and replaced without ith t any further f th rectification tifi ti d i during th the assembly stage, without affecting the f ti i functioning off the th componentt when h assembled
NECESSITY OF THE LIMIT SYSTEM If components are to be interchangeable, they need to be manufactured to the same size which is not possible, when they are mass produced. It becomes b necessary to t the th operator t to t deviate d i t by a small margin from the exact size (BASIC SIZE). SIZE) At the same time,, the deviated size should not affect the quality of the assembly. This sort of dimensioningg is known as limit dimensioningg
A system of limits A system of limits is to be followed as a standard is to be followed as a standard for the for the limit dimensioning of components Various system of limits and fits are followed by different Various system of limits and fits are followed by different countries based on the ISO specifications. The system of limits and fits followed in our country is that Th t f li it d fit f ll di t i th t stipulated by the BIS(BUREAU OF INDIAN STANDARDS) OTHER SYSTEM OF LIMITS AND FITS INTERNATIONAL STANDARDS ORGANISATION (ISO) BRITISH STANDARD SYSTEM (BSS) GERMAN STANDAD (DIN) ( )
TERMINOLOGY‐ THE INDIAN STANDARD SYSTEM OF LIMITS & FITS Size: It is a number expressed in a particular unit in the measurement of length Basic Size: It is the size based on which the dimensional deviations are given. Actual Size: It is the size of the component by actual measurement after it is manufactured. It should lie between the two limits of size if f d h ld l b h l f f the component is to be accepted
Limits of size: These are the extreme permissible sizes within which the operator is expected to make the component. Maximum limit of size: It is the greater of the two limit of sizes. Minimum limit of size: It is the smaller of the two limits of sizes. Hole: In the BIS system of limits & fits, componentt including i l di those th which hi h are nott as “Hole” Shaft: In the BIS system of limits & fits, component including those which are not as shaft.
all internal features of a cylindrical li d i l are designated d i t d
all external features of a cylindrical are designated
HOLE
SHAFT
Deviation: It is the algebraic difference between a limits of size to its corresponding basic size. It may be positive, negative or zero. Upper deviation: pp It is the algebraic difference between the maximum limit of size to its corresponding basic size maximum limit of size to its corresponding basic size. Lower deviation: It is the algebraic difference between the minimum limit of size to its corresponding basic size.
Actual deviation It is the algebraic difference between the actual size and its corresponding basic size. p g Tolerance: It is the difference between the maximum limit of size and minimum limits of size. It is always positive and is expressed only as a number without a sign is expressed only as a number without a sign. Zero line: In graphical representation of above , the zero line represents the basic size. This line is also called as the line of zero deviation.
• Is there any two things identical ?
• Why Variations? Wh V i ti ?
NO
Men M hi Machine Material
SHAFT BASIC DIAMETER 20MM
20mm
SHAFT DIAMETER : MAY GO UP TO 20.3 mm
20.3 mm
SHAFT SPECIFICATION
+ 0.30 - 0.00
20
?
SHAFT SPECIFICATION
+ 0.30 - 0.00
20
TOLERANCE
Dimensions and Tolerance communicate in the size and shape of the part. A Dimension A Di i is a numerical value expressed in i i l l di appropriate units of measure and used to define Size, location orientation form or other geometric location, orientation, form or other geometric characteristics of the part.
A Tolerance is the total amount that part features are permitted to vary from their specified dimensions. It is the difference between the maximum and minimum limit i i li i
SOLVE THE PROBLEM
ON THE DRAWING WHICH LETTER INDICATES A LIMIT TOLERANCE? ON THE DRAWING,WHICH LETTER INDICATES A LIMIT TOLERANCE?
ON THE DRAWING, WHICH LETTER INDICATES A PLUS OR MINUS TOLERANCE?
Fundamental Deviation: Th There are 28 fundamental f d t l deviations d i ti i the in th BIS system t represented by letter symbols The fundamental deviations are for achieving the different classes of fits
Schematic representation of the positions of fundamental deviations
Fundamental tolerance: This is also called ‘grade of tolerance’. In the Indian g Standard System , there are 18 grades of tolerances
A high number gives a _____________ tolerance zone.
LARGE A high number gives a _____________ tolerance zone.
Toleranced size: This includes the basic size, the fundamental deviation and the grade of tolerance.
25H7( toleranced size of a ___________)
HOLE
25H7( toleranced size of a ___________)
30h7 ( toleranced size of a _____)
Shaft 30h7 ( toleranced size of a _____)
Calculate the tolerance for a. 25H7 b. 30h7 b. 30h7
NO.
SIZE OF THE COMPONENT
UPPER DEVIATION
LOWER DEVIATION
MAX. LIMIT OF SIZE
MIN, LIMIT OF SIZE
Exercise : : Exercise 120 G7 20 g6
NO.
SIZE OF THE COMPONENT
UPPER DEVIATION
LOWER DEVIATION
MAX. LIMIT OF SIZE
MIN, LIMIT OF SIZE
FITS
Fit: It is the relationship that exists between two mating parts, a hole and a shaft., with respect to their dimensional diff difference between assembly b bl Expression of a fit: Example 30 H7/g6 (or) 30 H7‐g6 (or) 30
H7 g6
TYPES
1 Cl 1. Clearance Fit Fit
Clearance: In a fit the clearance is the difference between the size of the hole and the size of the shaft which is the size of the hole and the size of the shaft which is always positive. Clearance fit: It is a fit which always provides clearance. Here the tolerance zone of the hole will be above the tolerance zone of the shaft.
Clearance: In a fit the clearance is the difference between the size of the hole and the size of the shaft which is the size of the hole and the size of the shaft which is always positive. Clearance fit: It is a fit which always provides clearance. Here the tolerance zone of the hole will be above the tolerance zone of the shaft.
The limits of the hole are 20 + 0.021 = 20.021 mm 20 + 0 = 20.000 mm For a shaft 20 g6 we find in the table ‐7 ‐20 20 So the limits of the shaft are 20 ‐ 0.007 = 19.993 mm 20 ‐ 0.020 = 19.980 mm
Maximum clearance: In a clearance fit or transition fit, it is the difference In a clearance fit or transition fit it is the difference between the maximum hole and minimum shaft Minimum clearance: In a clearance fit, it is the difference between the minimum hole and maximum shaft
The minimum clearance is The minimum clearance 20.000 – 19.993 = 0.007 mm Th The maximum clearance i l i is 20.021 – 19.980 = 0.041 mm
There is always a clearance between the hole and the shaft. This is the Clearance fit.
2 I t f 2. Interference Fit Fit
Interpret the following 25H7/p6
Interference: It is the difference between the size of the hole and the shaft before assembly, and this is negative. In this case, the shaft is always larger than the hole size. Interference fit: It is a fit which always provides interference. Here the y p tolerance zone of the hole will be below the tolerance zone of the shaft.
Maximum Interference: Maximum Interference: In an interference fit or transition fit, it is the algebraic difference between the minimum hole and the maximum shaft. Minimum Interference: In an interference fit, it is the algebraic difference In an interference fit it is the algebraic difference between the maximum hole and the minimum shaft The maximum interference is The maximum interference 25.035 – 25.000 = 0.035 mm Th The minimum interference i i i t f i is 25.022 – 25.021 = 0.001 mm
3 T 3. Transition Fit iti Fit
Interpret the following 75 H8/j7 75 H8/j7
Transition fit: Transition fit: It is a fit which may sometimes provide clearance, and sometimes interference. When this class of fit is represented graphically the tolerance zones of the hole and shaft will overlap each other. Example; The limits of the hole are 75.046 mm (Max.limit of size) 75.000 mm (Min.limit of size) The limits of the shaft are 75.018 mm (Max.limit of size) ( ) 74.988 mm (Min.limit of size)
Max. clearance = Max. limit of hole – Max clearance = Max limit of hole Min. limit of shaft Min limit of shaft = 75.046 ‐74.988 = 0.058mm Max. interference = Max. limit of shaft – Min. limit of hole = 75.018 – 75.000 = 0.018 mm
This is a transition fit because it can result in a clearance fit or an This is a transition fit because it can result in a clearance fit or an interference fit.
BASIC SHAFT SYSTEM FIT
SHAFT HOLE
CLEARANCE
h
A up to H
TRANSITION
h
J up to N
INTERFERENCE
h
P up to ZC
BASIC HOLE SYSTEM FIT
HOLE
SHAFT
CLEARANCE
H
a up to h
TRANSITION
H
j up to n
INTERFERENCE
H
p up to zc
T Types of System fS t
In the BASIC HOLE system, the basic part is the hole, while the shaft is the mating part shaft is the mating part. In the BASIC SHAFT system, the basic part is the shaft, while the hole is the mating part. o e s t e at g pa t
Group Exercises
Determine Determine the type of fit
Determine Determine the type of fit
Determine the type of fit f fi
Identify the types of fits 30H7 / g6 / 30H7 / p6 30H7 / p6 30H7 / m6 30H7 / m6
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