Introduction

  British standards (BS) accepted as national
  guidelines for industry

  BS:
    Defines the standards for...
What is a dimensional tolerance?

  Virtually impossible to achieve exact required
  size of an item

  Permissible error ...
Factors affecting choice of DT

  Method of manufacture
    capability or accuracy of the process

  Size of item
    Smal...
Desired quality
   Higher quality implies a smaller tolerance

Material characteristics
   Allowable expansion due to temp...
Application of DT’s

  Can be applied in two ways:

1. General tolerances

  Applies to all dimensions in drawing

  Usual...
2. Individual tolerances

   Tolerance for a particular dimension only

   Usually for functional (critical) dimensions


...
Examples of tolerance




Individual
                                          General
Tolerance
                         ...
F1 - Trolley Housing




                       Dimensional Tolerance
F2 - Hinge

Smallest gap:


Smallest hole = 15mm
Widest pin = 15 - 0.021
= 14.979mm


Smallest gap = 0.021
mm

           ...
F3 - Machine Component




                         Dimensional Tolerance
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Dimensional Tolerances

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Dimensional Tolerances

  1. 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. 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. 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. 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. 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. 6. 2. Individual tolerances Tolerance for a particular dimension only Usually for functional (critical) dimensions Individual Tolerance General Tolerance Dimensional Tolerance
  7. 7. Examples of tolerance Individual General Tolerance Tolerance Dimensional Tolerance
  8. 8. F1 - Trolley Housing Dimensional Tolerance
  9. 9. F2 - Hinge Smallest gap: Smallest hole = 15mm Widest pin = 15 - 0.021 = 14.979mm Smallest gap = 0.021 mm Dimensional Tolerance
  10. 10. F3 - Machine Component Dimensional Tolerance

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