# Limits,tolarence and fits

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12-Sep-2014Category

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Interchangeable Manufacture, Terminology for Limits & Fits

Interchangeable Manufacture, Terminology for Limits & FitsPresented ByMd. Ashfaqur RahmanID:10.01.07.077

Interchangeable ManufactureDefinitionThe interchangeable manufacture implies that, the parts that are for practical purposes identical. They are made to specifications by processes that ensure that they are so nearly identical that they will fit into any device of the same typeExamples of Interchangeable Manufacture

Bottle caps

Rims

TiresAdvantages For Interchangeable ManufactureReplacement: One such part can freely replace another, without any custom fitting (such asfilling). Easy to Assembly: This interchangeability allows easy assembly of new devicesRepairing: Easier repair of existing devices.Minimizing time and cost :Minimizing both the time and skill required of the person doing the assembly or repair.Rapid Manufacturing :Machine tool enables the components to be manufactured more rapidlySize:- It is a number expressed in a particular unit in the measurement of length.Terminology for LIMITS & FITS Terminology:- The terms related to limit system are as below: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.

HoleShaftBasic SizeLimits of size:- These are the maximum and minimum permissible sizes of the part. Maximum limit:- Is the maximum size permitted for the part. Minimum limit:- it is the minimum size permitted for the part limit of size.Hole:-Refers to diameter of a circular hole as well as to any internal dimension of component .it is referred as femaleShaft:-Limits and fits, all external features of a component including those which are not cylindrical are designated as Shaft'. It is referred as male

HoleShaftBasic sizeTerminology for Limits and Fits Cont. Lower limit = 27. 8 0.2Upper limit = 28 . 2HoleTerminology for Limits and Fits Cont. Tolerance zoneTolerance :Tolerance is the difference between maximum limit of size and minimum limit of size.28(Basic)Zero lineAllowanceIt is an intentional difference between the maximum material limits of mating parts, For shaft, the maximum material will be its high limit and for hole, it will its low limit

Different Types of limitUnilateral Limit: In this method of presenting the limits, both the limits of size are on the same side of the zero line.

Bilateral Limits: Here one of the limits is on one side of the zero line And the other limit of size is on the other side of the line.

Zero lineActual Deviation:- It is the algebraic difference between actual size and its corresponding basic size. Deviation:- It is the algebraic difference between a size, to its corresponding basic size. It may be positive, negative or zero. Upper Deviation:- It is the algebraic difference between maximum limit of size and its corresponding basic size. Lower Deviation:- It is the algebraic difference between minimum limit of size and its corresponding basic size.

Max.dia.Min.dia.Upper DeviationLower DeviationMin.dia.Max.dia.ShaftDeviationsHoleFitFit is the relationship that exists between two mating parts, a hole and shaft with respect to their dimensional difference before assembly. Three types of fit are given hereunder;Clearance Fit : In clearance Fit shaft is always smaller than the hole. A positive allowance exists between the largest possible shaft and smallest possible hole.Minimum Clearance : It is the difference between the maximum size of shaft and minimum size of hole.Maximum clearance: It is the difference between the minimum size of the shaft and the maximum size of hole

Hole basis

Shaft Basis

Fit Cont.Interference Fit: It is also called Press or force fit, In this fit shaft is always larger than the holeMinimum interference: it is the difference between the maximum size of hole and the minimum size of shaft prior to assemblyMinimum Interference: It is the difference between the minimum size of the hole and the maximum size of the shaft prior to assembly.

ShaftHoleFit Cont.Transition Fit: it is called sliding Fit . It occurs when the resulting fit due to the variations in size of the male and female components due to their tolerance, varies between clearance and interference fits. The tolerance zones of shaft and hole overlap

ShaftHoleHole Basis SystemShaft Basis SystemHole is keep constant and the shaft diameter is variedThe basic size of the hole is taken as the low limitThe high limit of the size of the hole and the two limits of size of the shaft are selected to give the desired fitThe actual size of the hole is within the tolerance limit.In this system Hole gets the letter H and the shaft gets letter o decide the position of tolerance

Shaft is kept constant and the hole diameter is varied.The basic size of the shaft is taken as one of the limits(maximum) of size of shaftThe other limit of size of the shaft and the two limits of hole are then selected to give the desired fitThe actual size of a hole that is within the tolerance limits is always less than the basic size.In this system Shaft gets the letter h and the hole gets different letter o decide the position of the tolerance zone to obtain desired fit

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