NEED OF LIMITS FITS amp TOLERANCES Human inaccuracy errors lack of sophistication nature of job material TERNOLOGY Nominal Size It is the size represented on the drawing Basic Size ID: 779845
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Slide1
LIMITS FITS AND TOLERANCES
Slide2NEED OF LIMITS, FITS & TOLERANCES
Human inaccuracy, errors ,lack of sophistication ,nature of job material .
Slide3TERNOLOGY
Nominal Size:
It is the size
represented on the drawing
. Basic Size : It is the theoretical size to which limits of size are applied.Actual Size: is the measured size of the finished part.Limits of size: is the extreme permissible size of mating parts.Maximum and minimum limit size
Slide4Tolerance:
the permissible variation in size.
Tolerance
zone:
B/W max. &min. limit size .
Deviation: is the diff. b/w the basic size and the given size.Upper Deviation: is the diff. b/w the basic size and the permitted maximum size of the part.Lower Deviation: is the diff. b/w the basic size and the minimum permitted size of the part.
Slide5Fundamental Deviation:
is the deviation closest to the basic size.
Zero line: is the diff. b/w the permitted minimum and maximum sizes of a part.
Slide6Tolerances
The Tolerance is 0.001
”
for the Hole as well as for the Shaft
Slide7Allowance &
Clearance
Allowance is diff. b/w two mating parts
Slide8Fits Between Mating Parts
Fit :
Degree of tightness or looseness b/w two mating parts.
Three types
Clearance Fit:
clearance is left between the parts.Minimum air space is 0.002”. This is the allowance and is always positive in a clearance fit
Slide9Interference Fit:
The internal member is larger than the external member l. The smallest shaft is 1.2513
”
and the largest hole is 1.2506
”
,. This interference is the allowance, and in an interference fit it is always negative.
Slide10Transition Fit:
may result in either a clearance or interference condition.
eg the smallest shaft 1.2503
”
will fit in the largest hole 1.2506
”, with 0.003 +ve allowance. But the largest shaft, 1.2509” will have to be forced into the smallest hole, 1.2500” with –ve allowance of 0.009”.
Slide11Slide12Hole basis system
Minimum hole is taken as the basic size, an allowance is assigned, and tolerances are applied on shaft.
Maximum shaft is taken as the basic size, an allowance is assigned, and tolerances are applied on hole.
Shaft basis system
Slide13Slide14Specifications of Tolerances
Limit Dimensioning
The high limit is placed above the low limit.
In single-line note form, the low limit precedes the high limit separated by a dash
Slide15Specifications of Tolerances
Plus-or-minus Dimensioning
Unilateral Tolerance
Bilateral Tolerance
Slide16Tolerances representation
LEAST & MAXIMUM MATERIAL CONDITION
When a work piece contains max. or least amount of material
In max. and min. limit size of that work piece respectively.
Max. material condition :- min. hole size & max. shaft size.
Min. material condition :- max. hole size & min shaft size
Slide17International Tolerance Grade (IT):
They are a set of tolerances that varies according to the basic size and provides a uniform level of accuracy within the grade.
Slide18DIFFERENT LIMIT SYSTEMS
The Newall system
British standard system
ISO system
ISI system
Slide19Usage of standards for deciding tolerance