PE theory

PRODUCTION

Limitations of Selelctive Assembly :

i) Major limitations is some of the groups of the components are getting accumulated because of non uniform
distribution of component produceel.

ii) During the usage, if one part fails, first refer the manual & identifythat the failured component belongs to
which group and search for the corresponding group of component in different spare part shop.

Limit Gages :
Gages used for inspecting the limits of the components is called Limit Gages.
2 Methods of inspection
i) Inspection by variables
ii) Inspection by attributes

i) In each & every dimensions of a component is mesured by using some equipment, if the dimension falls
within the specified limits, the component is said to be acceptable out of the limits, component is refected.
This is called inspection by variables method.

It is time consuming process, costly, skilled persons are required for inspection & due to the continous
inection, the inspection may get fatigue and measures the wrong dimensions. So it is possible to accept the
rejectable components.

ii) Without actual measurement of dimension of a component byinspecting the component using limit gages,
the decision of accepting or rejecting a component is taken called as inspection byatributes methodology. In
limit gage inspection two components are used. If gogage is entering into component no gage is not entering
into components, component is said to be acceptable. If both gages are entering or both gages are not
entering, component is said to be rejectable.
Advantages : Fast, cheaper, no fatigue, unskilled labour.

Go gage should always enter into the acceptable components & the size of the go gage is made
equal to the maximum material limit of the component. The no gogage should not enter into two acceptable
components & the size of no go gage is made equal to the minimum material limit of the component. The
length of gogage is atleast equal to length of component where as the length of no gogage is only length.

Eg. : XXXXXXXXXXX L
XXXXXXXXXXX
+0.2 <>
50 - 0.1

<>  Copyright : Ascent Gate Academy 151

49.9

<>

50.2

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MECHANICAL ENGINEERING

<>> L GO NO GO

<> <>

49.9 50.2

* Gogage enters into component if material present in component is < maximum material limit.
* No gogage, does not enter, material present in component > minimum material limit i.e. minimum material
< material < maximum material.

If Gogage is not entering component material on component > maximum material limit. If nogage is
entering, material present < minimum material limit, so rejected.

Inspection of holes :
1) Plug gages : Divided into 3 types
a) Solid type plug gages
b) Renewable type plug gages
c) Progressive type plug gages

a) Solid type Fig : Solid type double gages.
i) Single ended
ii) Double ended

b) Renewable type (hollow type)

Go No Go Fig : Renewal type double ended.

49.9 50.2

<> <>

Fig : Renewal type single ended.  Copyright : Ascent Gate Academy 152
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c) Progressive : PRODUCTION

No Go Go

Inspection of Shafts : 3 type of gages :
i) Ring gages
ii) Gap gages
ii) Snap gages

i) Ring gage :

XXXXXXXXXXX GO > L NO GO
XXXXXXXXXXX L - shaft
<>
<> <>
L
< H - Limit >
< L -Limits > of shaft
<>

H -Limits

ii) Gap gage :

<> > Acceptable Shaft
<>
NO GO GO

By providing pins of different lengths, same gap gage can be used for inspecting different varieties of dimen-
sions of components. Gap gage with provision of pin is called snap gage.

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MECHANICAL ENGINEERING

Inspection of tapered hole :

>Recess or tolorence

When ever top surface of component is lying in between the limits of recess, componant is acceptable.
The tapered plug gages are always toleranced at the big end side only. (to have visibilited from top).

Tapered ring gages are always toleranced on small end side.

Design of Limit gages

There are 3 principles which are to be maintained during desiging of limit gages :
1) Basic Principle -According to this the design of limit gages can be such that no rejectable components
can be accepted but there is no problem in rejecting the acceptable components.
2) Taylors Principle -According to Taylor’s principle, the gogage is made for maximum material limit & it
has to incorporate as many dimensions as it is possible to inspect in one stroke at one stage. Where as no go
gage can be made for minimum material limit & separate no go gage has to be used for each & every
dimensions.

25 + 0.05 <>
+ 0.00

<>

40 +0.05
+0.00

<> NO GO 1

25 GO < 40.05 >

NO GO 2

< 40 > < 25.05 >

Note : If separate go gage are used, it is possible to accept rejectable compound.

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PRODUCTION

3) Principle of provision of limits & tolerence on Limit gages :

During manufacturing of gages, it is again difficult to manufacuture them due to man, machine &
material , so it is necessary to provide some amount of limit & tolerances on limit gages so that it ensure the
basic principle. On the limit gages, it is always preferable to provide unilateral tolerances.

Generally amount of tolerance provided on limit gages = 5 to 10% of the work tolerance.

i.e. Gage tolerance = 5 to 10% of work tolerence
& wear allowance = 5 to 10% of work tolerance

+0.06
-0.04

******************

“Luck is a dividend of sweat. The more you sweat ,
the luckier you get”

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