Tolerancing and Interchangeability
Tolerancing is dimensioning for interchangeability.
What is interchangeability?
An interchangeable part is simply a mass produced part (a replacement part).
How is a feature on an interchangeable part dimensioned?
A single value dimension (1.00) now becomes a range of values (.995 - 1.005).
A tolerance is the amount of size variation permitted. You can choose a tolerance that specifies a large or small variation.
Tolerance = max. size - min size
Why do we want a part’s size to be controlled by two limits?
It is necessary because it is impossible to manufacture parts without some variation. The stated limits are a form of quality control.
Choosing a tolerance for your design.
Specify a tolerance with whatever degree of accuracy that is required for the design to work properly. Choose a tolerance that is not unnecessarily accurate or excessively inaccurate. Choosing the correct tolerance for a particular application depends on:
- the design intent (end use) of the part
- cost
- how it is manufactured
- experience