What is Fits?
Fits in hindi me:- The parts which are interconnected in the machines are found with different features. Some parts get stuck together while some parts are found absolutely free (iska matlab without friction) and some parts move inside others. In this way the parts stay in each other’s fit as needed, so it can be said.
The connection between two parts (hole and shaft) that meet together is called a fit. It depends on the size of both the parts. To represent this, the deviation of the hole first and then the deviation of the shaft is given next to the basic size;
eg -20H7/g6 or 20H7-g6
More Information:- about the deviation
A fit in which the smallest size of the hole is greater than the larger size of the shaft is called a clearance fit. There is always a positive allowance. Here the tolerance zone of the hole lies above the tolerance zone of the shaft and some clearance also remains in between.
There are two types of clearance fit
(a.) running fit
Positive allowance is maximum in this fit. For this reason the shaft can easily rotate in the hole size, running fit is given inside the shaft and bush.
(b.) sliding fit
It also has positive allowance but less than running fit. In this, the shaft fits tightly into the hole size. It does not go very easily, but force is not required. In blacking and punching die, sliding fit is given inside the punch and die.
In this fit, the allowance between the hole and shaft is so placed that neither much clearance nor interference is there in it.
(a.) pus fit
This type of fit has neither much clearance nor interference, only the parts can be slided by presser of hand.
In this type of fit the shaft size is always greater than the hole size. The interference is denoted by the difference between the lower limit of the hole size and the upper limit of the shaft size. The allowance in an interference fit is always negative ( negative) occurs. In this the tolerance zone of the hole is always below the tolerance zone of the shaft.
In interference fit, the shaft is forced into the hole. These fits come in it.
(a.) driving fit
In this type of fit, the interference is placed only in such a way that the shaft can be fitted into the hole by hammer. This fit is given in shaft and pulley or gear, shaft and bearing etc.
In this the hole size is of shaft size Expectation gets smaller. So that the parts can be fitted when force is applied by the press. Eg:- Fitting the sleeve in the cylinder.
In this, the allowances on both the parts are kept in such a way that when the hole is heated, the shaft can easily come into it. And when it is cold, shrink the hole size and hold the shaft forcefully.
More Information:-about the deviation