1. Introduction
British standards (BS) accepted as national
guidelines for industry
BS:
Defines the standards for technical criteria,
manufacturing and health and safety
Simplifies and rationalises manufacturing
Encourages interchangeability
Enables effective communication
Dimensional Tolerance
2. What is a dimensional tolerance?
Virtually impossible to achieve exact required
size of an item
Permissible error = tolerance
If the tolerance affects the overall size then it
is called a dimensional tolerance
Dimensional Tolerance
3. Factors affecting choice of DT
Method of manufacture
capability or accuracy of the process
Size of item
Small things have a smaller tolerance
Allowable cost
Smaller tolerance is more expensive
Dimensional Tolerance
4. Desired quality
Higher quality implies a smaller tolerance
Material characteristics
Allowable expansion due to temperature
variations
Interfaces
Alignment and fit of a product
Standards
Specified in various British Standards
Dimensional Tolerance
5. Application of DT’s
Can be applied in two ways:
1. General tolerances
Applies to all dimensions in drawing
Usually shown in the title block
Usually applies to non-functional dimensions
Dimensional Tolerance
6. 2. Individual tolerances
Tolerance for a particular dimension only
Usually for functional (critical) dimensions
Individual Tolerance General Tolerance
Dimensional Tolerance
