Limits
In a manufacturing industry, it is not
possible to produce a part with required accuracy. It will consist of some error, because in
mass production, a large number of parts are to be made with different matches
by different operators. So, in mass
production, accuracy increases the cost ofk production and time kof production.
So it is obvious that some permissible
variations is allowed for manufacturing a part without affecting their
applications. The 2 limits of allowable
variation from the basic size is known as Limits.
Tolerance
Tolerance is the permissible variation in the
size. That is the difference lbetween
higher limit and lower limit of the part.
Depending upon the size, the tolerance is of 2
types.
a) Unilateral tolerance
Here the tolerance will vary in only one
direction of the basic size, either positive or negative.
b) Bilateral tolerance
Here, the tolerance is allowed to vary in 2
directions of the basic size.
Fits
Fits are defined as the looseness or tightness
of the 2 matting parts (hole and shaft).
So a fit will result in a movable or fixed joint.
Types of Fits
a) Clearance Fit
When the lower limit of hole is larger than the
jkupper limit of shaft then the fit is said to be clearance fit. Here hole and shaft have relative movement
with each other.
Examples: Slide
fit
Easy
slide fit
Running
fit
b) Interference fit
Here the lower limit of shaft is larger than
the upper limit of hole. So lno relative
movement is possible in interference fit.
Examples : Force
fit
Tight
fit
c) Transition fit
Here the limits of the hole or shaft lies in
between the other. It is the fit lines
in between clearance and transition fit.
Examples: Push
fit
Wringing
fit
