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**Lecture 2 – Clearance Fits**

EML 2023 – Clearance Fits Lecture 2 – Clearance Fits

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Cylindrical Fits

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**Cylindrical Fits – English Units**

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**Cylindrical Fits – English Units**

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**Cylindrical Fits – English Units**

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**Cylindrical Fits – English Units**

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**Cylindrical Fits – English Units**

tolerance - difference between the limits of size for a single feature ; shaft ; hole .0040 limits of tolerance – the max and min sizes of a single feature allowance – the tightest fit between two mating parts ; .0050 nominal size – the general size of a shaft or hole ; 1.5 basic size – the size to which the plus-and minus is applied actual size – the measured size of the finished part fit - the degree of tightness or looseness between two assembled parts

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**Cylindrical Fits – English Units**

clearance fit – gives a clearance between two assembled mated parts ; min clearance .005 ; max clearance .0115 transition fit interference fit line fit

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**Cylindrical Fits – English Units**

clearance fit interference fit – a binding fit that requires the parts to be forced together, much as if they were welded transition fit – may range from a interference fit to a clearance fit between the mated parts line fit – results in surface contact or clearance when limits are reached

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**Cylindrical Fits – English Units**

The ANSI B4.1 standard defines a series of fits between cylindrical features in inches for the basic hole system. The types of fits covered in the standard are: RC: running or sliding clearance fits LC: clearance locational fits LT: transition locational fits LN: interference locational fits FN: force and shrink fits

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**Cylindrical Fits – English Units**

RC: running or sliding clearance fits RC1 to RC9 LC: clearance locational fits LC1 to LC11 LT: transition locational fits LT1 to LT6 LN: interference locational fits LN1 to LN3 FN: force and shrink fits FN1 to FN5

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**Example – RC9 Fit hole and shaft have a basic diameter of 2.5”**

From Tables in Appendix 29 thousands of an inch

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**Example – LT3 Fit hole and shaft have a basic diameter of 2.5”**

From Tables in Appendix 31 2.5012 2.5000 2.5008 2.5001 thousands of an inch

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**Example – LN2 Fit hole and shaft have a basic diameter of 2.5”**

From Tables in Appendix 32 2.5012 2.5000 2.5021 2.5014 thousands of an inch

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Example Problem

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**Cylindrical Fits – Metric Units**

ANSI B4.2 standard basic size – the diameter from which limits are calculated upper and lower deviation – the difference between the hole or shaft size and the basic size tolerance - the difference between the maximum and minimum sizes

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**Cylindrical Fits – Metric Units**

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**Cylindrical Fits – Metric Units**

fundamental deviation – a letter grade that describes the deviation closest to the basic size International Tolerance (IT) grade – a series of tolerances that vary with the basic size to provide a uniform level of accuracy within a given grade there are 18 IT grades: IT01, IT0, IT1, …, IT16

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**Cylindrical Fits – Metric Units**

Hole basis a system of fits based on the minimum hole size as the basic diameter the fundamental deviation for a hole-basis system is “H” Appendices 35 and 36 give hole-basis data for tolerances Shaft basis a system of fits based on the maximum shaft size as the basic diameter the fundamental deviation for a hole-basis system is “h” Appendices 37 and 38 give shaft-basis data for tolerances

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**Cylindrical Fits – Metric Units**

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**Cylindrical Fits – Metric Units**

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**Example 1 determine the shaft and hole limits for: hole-basis system**

a close running fit a basic diameter of 49 mm use a preferred size

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Example 1 use a preferred basic diameter of 50 mm use a fit of H8/f7

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**Example 2 determine the shaft and hole limits for: hole-basis system**

a location transition fit a basic diameter of 57 mm use a preferred size

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Example 2 use a preferred basic diameter of 60 mm use a fit of H7/k6

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**Example 3 determine the shaft and hole limits for: hole-basis system**

a medium drive fit a basic diameter of 96 mm use a preferred size

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Example 3 use a preferred basic diameter of 100 mm use a fit of H7/s6

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**Nonstandard Fits, Nonpreferred Sizes**

determine the shaft and hole limits for: hole-basis system a close running fit a basic diameter of 45 mm (do not change to a preferred size)

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**Nonstandard Fits, Nonpreferred Sizes**

use a fit of H8/f7

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