DIMENSIONING & TOLERANCING

MANUFACTURING

1.Product involves assembly of parts.

2. Variability in dimensions (height, width,
depth, diameter, angle etc) of parts
manufactured -- due to variety of
reasons, some controllable and others not

3. This has implications for assembly of
parts.

In order to over come this practical situation


We need a DIMENSIONAL TOLERANCE


1. Is defined as the permissible or
acceptable variation in dimensions of a
part.

2. Tolerance is unavoidable as it is
impossible (and unnecessary) to
manufacture two parts that have
precisely the same dimensions.


TOLERANCE


1. Close tolerances implies precision
manufacturing and increases the cost of
production.

2. Hence the need for proper tolerance
based on product functionality.


SIMPLE ASSEMBLY

• HOLE and SHAFT

• TYPE OF FIT [Illustrative sample]

– Loose fit
– Free fit
– Snug fit
– Tight fit
– Medium force fit
– Heavy force shrink fit


IMPLICATIONS

1. If the fit is not OK the part might need
either rework or be scrapped.

2. Increases the cost of manufacturing.

3. Hence need to determine the economic
manufacturing tolerance while ensuring
functionality.


DEFINITIONS

1. Dimension:

A characteristic such as
length, angle, or diameter for which
magnitude is specified in the appropriate
unit of measurement.

2. Tolerance:

The total amount of variation
permitted for the size of a dimension, a
positional relationship or other design
requirement.
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