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7/21/2019 Limits and Tolerances
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Limit, Fit, Tolerance
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Size:- It is a number expressed
in a particular unit in the
measurement of length.
LIMITS, FITS T!L"#$%&"
Terminolog':- The terms related to limit s'stem as per(IS are as belo)*
(asic Size:- It is the size based
on )hich the dimensional
de+iations are gi+en.
$ctual Size:- It is the size of the component b' actual
measurement after it is manufactured. It should lie
bet)een the t)o limits of size.
ole
Shaft
B a si c S i z e
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Limits of size:- These are the extreme permissible
sizes )ithin )hich the operator is expected to mae
the component. Maximum limit of size is the greater
of the t)o limit size, )hereas the Minimum limit of
size is the smaller of the t)o limit of size.
ole:- In the (.I.S. s'stem of limitsand fits, all internal features of a
component including those )hich
are not c'lindrical are designated
as ole/.
Shaft:- In the (.I.S. s'stem of limits and fits, all
external features of a component including those
)hich are not c'lindrical are designated as Shaft/.
ole
Shaft
( a s i c s i z e
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$ctual 0e+iation:- It is the algebraic difference
bet)een actual size and its corresponding basic size.
0e+iation:- It is the algebraic
difference bet)een a size, to its
corresponding basic size. It ma'
be positi+e, negati+e or zero.
1pper 0e+iation:- It is the
algebraic difference bet)eenmaximum limit of size and its
corresponding basic size.
Lo)er 0e+iation:- It is the algebraic difference bet)eenminimum limit of size and its corresponding basic size.
Mi n . d i a .
Max.d i a.
ole
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2ero line:- In graphical representation of the abo+e
terms, the zero line represents the basic size. This line
is also called as the line of zero de+iation.
1 p p e r 0 e +i a t i on
L o ) e r 0 e +i a t i on
T
ol e r an c e
Mi n . d i a .
M
ax . d i a .
Shaft
ole
Tolerance:- It is the
difference bet)eenmaximum limit of size and
the minimum limit of size.
It is al)a's positi+e and is
expressed onl' as a number)ithout a sign.
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Fundamental de+iation:-
There are 34 fundamental
de+iations in the (.I.S.
s'stem represented b' letter,
s'mbols 5&apital letters for
oles and small letters forShaft6
M ax . d i a .
Mi n . d i a .
1 p p e r 0 e +i
a t i on
L o ) e r 0 e +i a t i on
T ol e r an c e
T ol e r an c e
Mi n . d i a .
Max.d i a.
Shaft
ole
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Fundamental Tolerance:-This is also called as
grade of tolerance/. In the
Indian Standard S'stem,
there are 78 gradesrepresented b' number
s'mbols, both for hole and
shaft denoted as IT97, IT9,
IT7, IT3.....IT7. $ high
number
M ax . d i a .
Mi n . d i a .
1 p p e r 0 e +i a t i on
L o ) e r 0 e +i a t i on
T ol e r an c e
Mi n . d i a .
M ax . d i a .
Shaft
ole
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FIT:- It is the relationship that exists bet)een t)o
mating parts, a hole and shaft )ith respect to their
dimensional difference before assembl'. Three t'pes of
fit are gi+en hereunder*
&learance fit:- It is a fit )hich
al)a's pro+ides clearance. erethe tolerance zone of the hole )ill
be abo+e the tolerance zone of the
shaft. Maximum clearance is the
difference bet)een the maximumhole and minimum shaft.
Minimum clearance is the
difference bet)een the minimum
hole and maximum shaft.
Shaftole
&learanc
e fit
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Interference fit:- It is a fit )hich
al)a's pro+ides interference.ere the tolerance zone of the
hole )ill be belo) the tolerance
zone of the shaft. Maximum
interference is the algebraic
difference bet)een the
minimum hole and maximum
shaft. Minimum interference isthe algebraic difference
bet)een the maximum hole and
minimum shaft.
Shaft
ole
Tolerance 2one of
ole
Tolerance 2one of
Shaft
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Transition fit:- It is a fit )hich
ma' sometimes pro+ides
clearance and sometimes
interference. ;hen this class of
fit is represented graphicall',
the tolerance zone of the hole
and shaft )ill o+erlap each
other.
ole ole
ole
ShaftShaft
Shaft
Mass <roduction :- Mass production means production
of a unit, component or part in large numbers.
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$d+antages:- 7.Time for the manufacture of
components is reduced
3.The cost of pieces is reduced. =.
Spare parts can be >uicl' made
a+ailable. 0isad+antages:-7. Specialpurpose machines are necessar'.
3.?igs and Fixtures are
needed. =. @auges are to be used
instead of con+entional precisioninstruments. A. Initial expenditure )ill be
+er' high.
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Interchangeabilit':- ;hen components are mass
produced, unless the' are interchangeable, the purpose of
mass production is not fulfilled. (' interchangeabilit', )e
mean that identical components, manufactured b'
different personnel under different en+ironments, can be
assembled and replaced )ithout an' further rectification
during the assembl' stage, )ithout affecting the
functioning of the component )hen assembled.
ole (asis S'stem:- ;here the
size of the hole is ept constantand the size of the shaft is +aried
to get the different class of fits,
then it is no)n as the hole basis
s'stem.
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Shaft (asis S'stem:- ;here the
size of the shaft is ept constant
and the +ariations gi+en to thehole to get the different class of
fits, then it is no)n as the shaft
basis s'stem.
(asic Shaft S'stem
2ero lineShaft
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