ALL GATE CONCEPTS MECHANICAL THEORY Production

3 Types of Fits-Clearance Fit,Transition Fit & Interference Fit,Selective Assembly

3 Types of Fits-Clearance Fit, Transition Fit & Interference Fit Every Engineer must know: The relationship between the hole and the shaft during the Assembly is called as Fit. The various parameters that can be included are Maximum Interference, Minimum Interference, Maximum Clearance, minimum clearance etc. In this article, I will be defining all these parameters w.r.t. the hole and shaft assembly. Each Fit in this article is represented by a condition which needs to be satisfied and extreme cases are shown w.r.t.the assembly. Read this article till the end so that you can understand 3 types of fits briefly.

3 Types of Fits-Clearance Fit,Transition Fit & Interference Fit Every Engineer must know-Interview

Contents:

1.Clearance Fit

2.Interference Fit

3.Transition Fit

4.Types of Assemblies used in Manufacturing

3 Types of Fits-Clearance Fit, Transition Fit & Interference Fit:

The brief explanation of all these types of fits was presented below.

1.Clearance fit:

The dimensions of hole and shaft are such that always clearance or gap is existing between hole and shaft called as Clearance fit.

Condition: Hole size must be greater than Shaft size.

clearance fit-TYPES OF FITS

Extreme Cases:

  • L.Hole v/s L.Shaft –>H>S —->Clearance Fit
  • L.Hole v/s H.Shaft –>H>S—–>Clearance Fit
  • H.Hole v/s L.Shaft –>H>S —->Clearance Fit
  • H.Hole v/s H.Shaft –>H>S —->Clearance Fit

As Hole size is greater than Shaft size, it is called as Clearance Fit.

Ex: Used in all the mating assemblies.

Maximum Clearance = higher limit of the hole lower limit of the shaft

                                        = Difference between minimum material limits.

Maximum clearance is also called as worst case clearance in the clearance fit.

Minimum Clearance = lower limit of the hole higher limit of the shaft.

                                       = Difference between maximum material limits.

2.Interference fit:

Dimensions of hole and shaft are such that without the interference of external agency the Assembly of hole and shaft is not possible.

Condition: Shaft size must be greater than Hole size.

interference fit-Types of Fits
Interference fit-Types of Fits

External agency for assembly:

a.Force/Pressure: that is by the application of force or pressure we can get the push fit.

b: Heating or Cooling: i.e. by the application of Heating or Cooling, we can get the shrink fit.

Extreme Cases:

  • L.Hole v/s L.Shaft –>S>H —->Interference is Required
  • L.Hole v/s H.Shaft –>S>H —->Interference is Required
  • H.Hole v/s L.Shaft –>S>H —->Interference is Required
  • H.Hole v/s H.Shaft –>S>H —->Interference is Required

According to the Transition Fit, in all the 4 cases interference is required. Let’s look at the Interference fit.

Ex: Used in non-mating assemblies like bearing bushes fitted into the bearing housing, key fitted into the keyway etc.

Maximum Interference = higher limit of the shaft – lower limit of the hole.

                                              = Difference between maximum material limits.

Minimum Interference=lower limit of the shaft – higher limit of the hole.

                                            = Difference between minimum material limits.

The power transmission capacity of interference fit is defined based on minimum interference only.

3.Transition Fit:

The dimensions of hole and shaft are such that sometimes the Clearance fit and sometimes the Interference fit is produced called as Transition fit.

transition fit-Types of fits

Condition:

According to the latest definition, if one of the components is lying in between higher and lower limits of the Other component produces transition fit.

Extreme Cases:

Case 1:

  • L.Hole v/s L.Shaft –>H>S —->Clearance Fit
  • L.Hole v/s H.Shaft –>H<S—–>Interference Fit
  • H.Hole v/s L.Shaft –>H>S —->Clearance Fit
  • H.Hole v/s H.Shaft –>H>S —->Clearance Fit

Case 2:

  • L.Hole v/s L.Shaft –>H<S —->Interference Fit
  • L.Hole v/s H.Shaft –>H<S—–>Interference Fit
  • H.Hole v/s L.Shaft –>H>S —->Clearance Fit
  • H.Hole v/s H.Shaft –>H<S —->Interference Fit

According to the above cases,the Transition fit sometimes produces Clearance Fit and Sometimes it is producing Interference Fit.

Therefore it is called Transition Fit.

Applications:

Used for producing non-mating assemblies like fit between Piston and Piston rings of IC engine, coupling, and coupling rings etc.

Types of Assemblies Produced in the Manufacturing Industry:

1. Make to suit assembly:

Out of the hole and shaft, one component is made first approximately near to the required dimension and the second component is made slowly such that it can be assembled into the first component according to the requirement assembly conditions.

Advantages:

because of no limits and no tolerances are provided on the component, there is no rejection of components will be present.

Disadvantages:

During usage of the assembly, if one component fails in the Assembly, the total assembly has to be brought it to one of the manufacturing industry and get it to manufacture the failure component which is difficult sometimes.

2.Interchangeable Assembly:

The parts manufactured under similar conditions by a company or a factory at any corner of the world can be interchangeable.

During usage of the Assembly, if M6 Bolt fails in the Assembly, simply bring another M6 bolt from the spare parts shop and replace it.

With interchangeable assembly, the customer is not facing any problem but when the components are manufactured in the industry with limits and tolerances, there must be some amount of rejection of components will be present.

3.Selective Assembly:

It is also one type of interchangeable assembly but only selected group of components can be interchangeable.

During usage of assembly, if group A, M6 Bolt fails in the Assembly, it has to be replaced by using another group A, M6 Bolt only.

Therefore it has the limited interchangeability hence when compared to interchangeable Assembly the selective assembly is inferior.

The selective assembly has been developed for manufacturing of very small tolerance components on a machine which has process capability.

It is the minimum tolerance of components which can be produced on a machine with more than 99% of acceptability.

Lowered the minimum tolerance indicate good process capability machining.

Procedure:

In selective assembly, by keeping one of the limits of a component remains constant, it enhances the tolerance of the component such that tolerance of the component should be greater than or equal to process capabilities of machining.

Manufacturing the components accordingly. Inspect them and after inspection divide the acceptable components into a number of groups such that each group of components will have tolerance less than or equal to the original tolerance.

Assemble the corresponding related group of a component so that the Assembly components are better than or same as that of original assembly conditions.

Advantages of selective assembly:

It is possible to produce very small tolerances components on a machine which has very poor process capability.

limitations of selective assembly:

Because of a number of components produced in each group or random, some group of components will get accumulated.

During usage of the assembly, if one component fails in assembly, first referred the manual of the assembly and identify the group to which the failure component belongs and then search in the different spare parts shop until the required group of the component is made available.

In spite of limitations, the selective assembly is used for manufacturing of ball bearing assemblies.

Read:

This is the complete explanation of all the 3 types of fits which are proved by the conditions and Extreme cases.

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