Limits,tolarence and fits


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Concept of Limits , Tolerance and Fits

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Limits,tolarence and fits

  2. 2. Interchangeable ManufactureDefinition The 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 type
  3. 3. Examples of InterchangeableManufactureBottle caps Rims Tires
  4. 4. Advantages For InterchangeableManufacture Replacement: One such part can freely replace another, without any custom fitting (such as filling). Easy to Assembly: This interchangeability allows easy assembly of new devices Repairing: 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 rapidly
  5. 5. Terminology for LIMITS & FITS Terminology:- The terms related to limit system are as below: Size:- It is a number expressed in a particular unit in the measurement of length. Basic Size Basic Size:- It is the size based Hole Shaft 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.
  6. 6. Terminology for Limits and Fits Cont. Limits 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 “female” Basic Hole size Shaft Shaft:-Limits and fits, all external features of a component including those which are not cylindrical are designated as ‘Shaft. It is referred as “male”
  7. 7. Terminology for Limits and Fits Cont.Tolerance :Tolerance is the difference between maximum limit of size andminimum limit of size. Tolerance zone Upper limit =  28 . 2 Zero line Lower limit =  27. 8 Ø28  0.2 (Basic) Hole
  8. 8. Allowance It is an intentional difference between the maximum material limits of mating parts, For shaft, the maximum material will be it’s high limit and for hole, it will it’s low limit
  9. 9. Different Types of limit Unilateral 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 Zero lineof the limits is on one side ofthe zero line And the otherlimit of size is on the otherside of the line.
  10. 10. Deviations Upper Deviation Lower Deviation  Deviation:- It is the algebraic difference between a size, to its corresponding basic size. It may be positive, negative or zero. Hole Upper Deviation:- It is theMax.dia. Min.dia. Max.dia. Min.dia. Shaft 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.Actual Deviation:- It is the algebraic difference between actual size and its corresponding basic size.
  11. 11. Fit Fit 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 isalways smaller than the hole. A positiveallowance exists between the largestpossible shaft and smallest possible hole. Minimum Clearance : It is the difference between the maximum size of shaft and Hole basis minimum size of hole. Maximum clearance: It is the difference between the minimum size of the shaft and the maximum size of hole Shaft Basis
  12. 12. Fit Cont. Interference Fit: It is also called Press or force fit, In this fit shaft is always larger than the hole Minimum interference: it is the difference between the maximum size of hole and the minimum size of shaft prior to Shaft assembly Hole Minimum Interference: It is the difference between the minimum size of the hole and the maximum size of the shaft prior to assembly.
  13. 13. Fit 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 Shaft Hole clearance and interference fits. The tolerance zones of shaft and hole overlap
  14. 14. Hole Basis System Shaft Basis System Hole is keep constant and the shaft  Shaft is kept constant and the hole diameter diameter is varied is varied. The basic size of the hole is taken as  The basic size of the shaft is taken as one of the low limit the limits(maximum) of size of shaft The high limit of the size of the hole  The other limit of size of the shaft and the and the two limits of size of the shaft two limits of hole are then selected to give are selected to give the desired fit the desired fit The actual size of the hole is within  The actual size of a hole that is within the the tolerance limit. tolerance limits is always less than the basic In this system Hole gets the letter H size. and the shaft gets letter o decide the  In this system Shaft gets the letter h and the position of tolerance hole gets different letter o decide the position of the tolerance zone to obtain desired fit
  15. 15. THANK YOU