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
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
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
• 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
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
2. Individual tolerances – Tolerance for a particular dimension only – Usually for functional (critical) dimensions
Individual Tolerance
General Tolerance Dimensional Tolerance
Examples of tolerance
Individual Tolerance
General Tolerance
Dimensional Tolerance
F1 - Trolley Housing
Dimensional Tolerance
F2 - Hinge Smallest gap: Smallest hole = 15mm Widest pin = 15 - 0.021 = 14.979mm
Smallest gap = 0.021mm
Dimensional Tolerance
F3 - Machine Component
Dimensional Tolerance