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Application of Limits and Fits BS 4500  To achieve different types of fit for mating components it is necessary to set the correct limits of size for.

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Presentation on theme: "Application of Limits and Fits BS 4500  To achieve different types of fit for mating components it is necessary to set the correct limits of size for."— Presentation transcript:

1 Application of Limits and Fits BS 4500  To achieve different types of fit for mating components it is necessary to set the correct limits of size for each part.  To do this it is necessary to consider the following factors.  Function of the parts  The environment they are in  Type of material  Type of finish required  Cost of production (process/s needed.  When all these have been considered then you can decide the type of fit needed and by reference to tables (BS4500) calculate limits of size.

2 Principal Terms of Limits and Fits

3  The outer component (Bearing) is described by the Nominal Size followed by Capital Letter and a Number e.g. 20 H6  The inner component (Shaft) is described by the Nominal Size followed by a Lower Case Letter and a Number e.g. 20 h6  The Letter specifies the Fundamental Deviation (tolerance position) in relation to the Nominal/Basic Size.  The Number specifies the Tolerance Grade (magnitude of tolerance) sometimes referred to as Fundamental Tolerance ISO System for Specifying Types of Fit

4  There are 28 designated standard deviations for shafts e.g. a, b, c, etc. and 28 designated standard deviations for holes/Bearings e.g. A, B, C, etc.

5 Clearance Interference

6  There are 18 tolerance grades (IT Grades) that can be applied to the Shaft and the Hole designated 01, 0,1,2…….16 The smaller the number the finer the tolerance

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8 Hole and Shaft Basis  To obtain a given type of fit between two mating components such as a shaft and a bearing two systems can be employed  Hole Basis System:- where the hole/bearing size remains constant and the shaft size changes to achieve the desired fit  Shaft Basis System:- Where the shaft size remains constant and the hole/bearing size changes to achieve the desired fit  The Hole Basis System is commonly used as it is easier to maintain a standard size of hole with the use of drills and reamers, whilst the shaft size can easily be changed during the turning and grinding process

9 Selected fits Hole Basis

10 Selected Fits Shaft basis

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