EML 2023 Clearance Fits Lecture 2 Clearance Fits

EML 2023 – Clearance Fits Lecture 2 – Clearance Fits

Cylindrical Fits EML 2023 Computer Aided Design 2

Cylindrical Fits – English Units EML 2023 Computer Aided Design 3

Cylindrical Fits – English Units EML 2023 Computer Aided Design 4

Cylindrical Fits – English Units EML 2023 Computer Aided Design 5

Cylindrical Fits – English Units EML 2023 Computer Aided Design 6

Cylindrical Fits – English Units tolerance - difference between the limits of size for a single feature ; shaft. 0025 ; 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 EML 2023 Computer Aided Design 7

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 EML 2023 Computer Aided Design 8

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 EML 2023 Computer Aided Design 9

Cylindrical Fits – English Units • The ANSI B 4. 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 EML 2023 Computer Aided Design 10

Cylindrical Fits – English Units • RC: running or sliding clearance fits – RC 1 to RC 9 • LC: clearance locational fits • LC 1 to LC 11 • LT: transition locational fits • LT 1 to LT 6 • LN: interference locational fits • LN 1 to LN 3 • FN: force and shrink fits • FN 1 to FN 5 EML 2023 Computer Aided Design 11

Example – RC 9 Fit • hole and shaft have a basic diameter of 2. 5” • From Tables in Appendix 29 thousands of an inch EML 2023 Computer Aided Design 12

Example – LT 3 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 EML 2023 Computer Aided Design 13

Example – LN 2 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 EML 2023 Computer Aided Design 14

Example Problem 15

Cylindrical Fits – Metric Units • ANSI B 4. 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 EML 2023 Computer Aided Design 16

Cylindrical Fits – Metric Units EML 2023 Computer Aided Design 17

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: IT 01, IT 0, IT 1, …, IT 16 EML 2023 Computer Aided Design 18

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 EML 2023 Computer Aided Design 19

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Cylindrical Fits – Metric Units EML 2023 Computer Aided Design 21

Cylindrical Fits – Metric Units EML 2023 Computer Aided Design 22

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 EML 2023 Computer Aided Design 23

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Example 1 • use a preferred basic diameter of 50 mm • use a fit of H 8/f 7 EML 2023 Computer Aided Design 25

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 EML 2023 Computer Aided Design 26

EML 2023 Computer Aided Design 27

Example 2 • use a preferred basic diameter of 60 mm • use a fit of H 7/k 6 EML 2023 Computer Aided Design 28

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 EML 2023 Computer Aided Design 29

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Example 3 • use a preferred basic diameter of 100 mm • use a fit of H 7/s 6 EML 2023 Computer Aided Design 31

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) EML 2023 Computer Aided Design 32

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Nonstandard Fits, Nonpreferred Sizes • use a fit of H 8/f 7 EML 2023 Computer Aided Design 34