Necessity
of concept: Practically it is impossible to manufacture thousand piece
of any product with exact dimensions. Therefore we fix range of dimensions i.e.
maximum size and minimum size of product so that we can select the product
comes within the range. In mechanical
Engineering Limits and Fits provides
a set of rules to solve this.
LIMITS - These
are two extreme permissible sizes of dimension between which actual size of
dimension is contained. The greater of these two is called higher limit and the
smaller lower limit.
FITS - It
is the degree of tightness or looseness between two mating parts to perform a
definite function.
The commonly used terms are:
- Basic size - the nominal dimensions of component.
- Lower deviation - the difference between the minimum possible component size and the basic size.
- Upper deviation - the difference between the maximum possible component size and the basic size.
- Tolerance - Permissible variation in size or dimension is called tolerance
- Fundamental deviation – It is the distance between the basic size and deviation closer to it. Either upper deviation or lower deviation.
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