limits and tolerances

7/21/2019 Limits and Tolerances

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Limit, Fit, Tolerance



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



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



$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



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.



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


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



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


T ol e r an c e

Mi n . d i a .

M ax . d i a .

Shaft

ole



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



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



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.



$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.



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.



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

limits and tolerances

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