ABOUT DEFINE FITS OR TYPES FITS

 WHAT IS DEFINE FITS?

• Dimensional tolerances deal with the permissible variations in the dimension of a component.
• However, when the two components are to be assembled, it is important to relate the dimensions of these two components to be assembled.
• The difference between the dimensions of the two components to be assembled is very important from the point of view of the assembly as well as the machine.
• Fits: When two parts are assembled, the type of assembly resulting in virtue of the difference between their sizes before assembly is called a fit.

• Types of Fits :

    

                   Depending upon the relative sizes of the hole and shaft, the fits are broadly classified               into  three types :

1. Clearance Fit:

• Clearance fit is the fit, which always provides a positive clearance between the hole and the shaft over the entire range of tolerances.
• In thi case,the tolerance zone of the hole is entirely above that of the shaft.
• In clearance fit, the minimum size of the hole is always larger than the maximum size of the shaft.
• Examples of clearance fit : sliding contact bearings, pin and bush, piston and cylinder, shaft and pulley, etc.

     2.  Interference Fit : 

• Interference fit is the fit, which always provides an interference over the entire range of tolerances.
• In this case, the tolerance zone of the hole is entirely below that of the shaft.
• In interference fit, the minimum size of the hole is always smaller than the minimum size of the shaft.
• Examples of interference fit : brass bush in gear, bearing bushes, valve seats, etc.

     3.  Transition Fit : 

• Transition fit is the fit, which may provide either a clearange or an interference , depending upon the actual value of individual tolerances of the mating parts. 
• In this case, the tolerance zones of the hole and the shaft overlap.
• Examples of transition fit : spigot and recess of rigid coupling, bimetallic gear blanks, key and keyway, etc.