British standards define technical, manufacturing, and safety guidelines for UK industry. Dimensional tolerances account for permissible errors in achieving exact sizes during manufacturing. The choice of tolerance depends on the manufacturing method, item size, cost considerations, desired quality, material properties, and interfaces. Tolerances can be general, applying to all non-functional dimensions, or individual, specifying tolerances for critical dimensions. Examples show individual tolerances for functional parts and a general tolerance in a title block.

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

7. Examples of tolerance
Individual
General
Tolerance
Tolerance
Dimensional Tolerance

8. F1 - Trolley Housing
Dimensional Tolerance

9. F2 - Hinge
Smallest gap:
Smallest hole = 15mm
Widest pin = 15 - 0.021
= 14.979mm
Smallest gap = 0.021
mm
Dimensional Tolerance

10. F3 - Machine Component
Dimensional Tolerance