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An in-depth analysis of tolerances and fits in engineering, discussing the impact of variability in machines, materials, and operators on manufacturing identical parts. It covers the concept of interchangeability, the effect of tolerance on production cost, and the importance of standard guidelines for choosing exact product dimensions. The document also explains the difference between unilateral and bilateral tolerances, the types of fits, and the role of allowances and limits.
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Two identical parts cannot be manufactured due to variability in machines, materials & operators Proper fit of various components ensures smooth functioning of product Permissible tolerance in the dimensions depends on the functional requirements Fig. 1: Effect of tolerance on production cost
Factors affecting the interchangeability of a component are specified by a drawing Manufactured parts are independent of skill, tooling or knowledge within a particular work-shop
Standard guidelines for choosing exact product dimensions within a given set of constraints Advantage of using preferred numbers:
Used when allowable difference is smaller than the normal permissible manufacturing conditions Parts are manufactured to a wider tolerance Components are classified into groups Matched groups of mating parts are assembled E.g. Assembly of ball and bearing units
Tolerance is:
Fig 2: Basic size, deviations, limits & tolerances
The high limit is placed above the low limit. In single-line note form, the low limit precedes the high limit separated by a dash
Unilateral Tolerance: Tolerance distribution is on only one side of the basic size Fig 3: Unilateral tolerance designation Bilateral Tolerance: Tolerance distribution lies on either side of the basic size Fig 4: Bilateral tolerance designation
Least Material Condition denotes: ◦ Lower limit of the Shaft ◦ Upper limit of the Hole Maximum Material Condition denotes: ◦ Lower limit of the Hole ◦ Upper limit of the Shaft
Signifies the range of tightness or looseness that may result from the application of a specific combination of allowances and tolerances in mating parts. Types of fits :
